Acetylene (C 2 H 2 ) is a trace constituent of Earth’s modern atmosphere and is used by acetylenotrophic microorganisms as their sole carbon and energy source (Akob et al. 2018) Acetylenotrophs hydrate acetylene through a reaction catalyzed by acetylene hydratase, which is a heterogeneous class of enzymes. As of 2018, there were 15 known strains of acetylenotrophs including aerobic species affiliated with the Actinobacteria, and Firmicutes and anaerobic species affiliated with the Desulfobacterota. However, we hypothesized that there was an unknown diversity of acetylenotrophs in nature. We recently expanded the known distribution of acetylenotrophs via the isolation of the aerobic acetylenotroph, Bradyrhizobium sp. strain I71, from trichloroethylene (TCE)-contaminated soils (Akob et al. 2022). Strain I71 is a member of the class Alphaproteobacteria, and this is the first observation of an aerobic acetylenotroph in the Proteobacteria phylum. The isolate grows via heterotrophic and acetylenotrophic metabolism, and is diazotrophic, capable of nitrogen fixation. Acetylenotrophy and nitrogen fixation are the only two enzymatic reactions known to transform acetylene, and this is only the second isolate known to carry out both reactions (Akob et al. 2017, Baesman et al. 2019). Members of Bradyrhizobium are well studied for their abilities to improve plant health and increase crop yields by providing bioavailable nitrogen. The unique capability of Bradyrhizobium sp. strain I71 to utilize acetylene may increase the genus’ economic impact beyond agriculture as acetylenotrophy is closely linked to bioremediation of chlorinated contaminants (Mao et al. 2017, Gushgari-Doyle et al. 2021). Based on genome, cultivation, and protein prediction analysis, the ability to consume acetylene is likely not widespread within the genus Bradyrhizobium . These findings suggest that the suite of phenotypic capabilities of strain I71 may be unique and make it a good candidate for further study in several research avenues such as contaminant biodegradation and nutrient cycling.

The isolation of Bradyrhizobium strain I71 expands the distribution of acetylene-consuming microbes to include a group of economically important microorganisms. Members of Bradyrhizobium are well studied for their abilities to improve plant health and increase crop yields by providing bioavailable nitrogen.

A Gram-stain-negative, strictly anaerobic, non-motile, rod-shaped bacterium, designated SFB93T, was isolated from the intertidal sediments of South San Francisco Bay, located near Palo Alto, CA, USA. SFB93T was capable of acetylenotrophic and diazotrophic growth, grew at 22-37 °C, pH 6.3-8.5 and in the presence of 10-45 g l-1 NaCl. Phylogenetic analyses based on 16S rRNA gene sequencing showed that SFB93T represented a member of the genus Syntrophotalea with highest 16S rRNA gene sequence similarities to Syntrophotalea acetylenica DSM 3246T (96.6 %), Syntrophotalea carbinolica DSM 2380T (96.5 %), and Syntrophotalea venetiana DSM 2394T (96.7 %). Genome sequencing revealed a genome size of 3.22 Mbp and a DNA G+C content of 53.4 %. SFB93T had low genome-wide average nucleotide identity (81-87.5 %) and <70 % digital DNA-DNA hybridization value with other members of the genus Syntrophotalea. The phylogenetic position of SFB93T within the family Syntrophotaleaceae and as a novel member of the genus Syntrophotalea was confirmed via phylogenetic reconstruction based on concatenated alignments of 92 bacterial core genes. On the basis of the results of phenotypic, genotypic and phylogenetic analyses, a novel species, Syntrophotalea acetylenivorans sp. nov., is proposed, with SFB93T (=DSM 106009T=JCM 33327T=ATCC TSD-118T) as the type strain.

In aquifers, acetylene (C2H2) is a product of abiotic degradation of trichloroethene (TCE) catalyzed by in situ minerals. C2H2 can, in turn, inhibit multiple microbial processes including TCE dechlorination and metabolisms that commonly support dechlorination, in addition to supporting the growth of acetylenotrophic microorganisms. Previously, C2H2 was shown to support TCE reductive dechlorination in synthetic, laboratory-constructed cocultures containing the acetylenotroph Pelobacter sp. strain SFB93 and Dehalococcoides mccartyi strain 195 or strain BAV1. In this study, we demonstrate TCE and perchloroethene (PCE) reductive dechlorination by a microbial community enriched from contaminated groundwater and amended with C2H2 as the sole electron donor and organic carbon source. The metagenome of the stable, enriched community was analyzed to elucidate putative community functions. A novel anaerobic acetylenotroph in the phylum Actinobacteria was identified using metagenomic analysis. These results demonstrate that the coupling of acetylenotrophy and reductive dechlorination can occur in the environment with native bacteria and broaden our understanding of biotransformation at contaminated sites containing both TCE and C2H2. IMPORTANCE Understanding the complex metabolisms of microbial communities in contaminated groundwaters is a challenge. PCE and TCE are among the most common groundwater contaminants in the United States that, when exposed to certain minerals, exhibit a unique abiotic degradation pathway in which C2H2 is a product. C2H2 can act as both an inhibitor of TCE dechlorination and of supporting metabolisms and an energy source for acetylenotrophic bacteria. Here, we combine laboratory microcosm studies with computational approaches to enrich and characterize an environmental microbial community that couples two uncommon metabolisms, demonstrating unique metabolic interactions only yet reported in synthetic, laboratory-constructed settings. Using this comprehensive approach, we have identified the first reported anaerobic acetylenotroph in the phylum Actinobacteria, demonstrating the yet-undescribed diversity of this metabolism that is widely considered to be uncommon.

In research, sometimes sheer happenstance and serendipity make for an unexpected discovery. Once revealed and if interesting enough, such a finding and its follow-up investigations can lead to advances by others that leave its originators 'scooped' and mulling about what next to do with their unpublished data, specifically what journals could it still be published in and be perceived as original. This is what occurred with us nearly 40 years ago with regard to our follow-up observations of acetylene fermentation and led us to concoct a 'cock-and-bull' story. We hypothesized about a plausible role for acetylene metabolism in the primordial biogeochemistry of Earth and the possibility of acetylene serving as a key life-sustaining substrate for alien microbes dwelling in the orbs of the outer solar system. With the passage of time, advances were made in whole-genome sequencing coupled with major in silico progress in bioinformatics. In parallel came the results of explorations of the outer solar system (i.e. the Cassini mission to Saturn and its moons). It now appears that these somewhat harebrained ideas of ours, arisen at first out of a sense of desperation, actually ring true in fact, and particularly well in song: 'Tell a tale of cock and bull, Of convincing detail full Tale tremendous, Heav'n defend us! What a tale of cock and bull!' From 'The Yeoman of the Guard' by Gilbert & Sullivan.

Arsenic is a toxin, ranking first on the Agency for Toxic Substances and Disease Registry and the Environmental Protection Agency Priority List of Hazardous Substances. Chronic exposure increases the risk of a broad range of human illnesses, most notably cancer; however, there is significant variability in arsenic-induced disease among exposed individuals. Human genetics is a known component, but it alone cannot account for the large inter-individual variability in the presentation of arsenicosis symptoms. Each part of the gastrointestinal tract (GIT) may be considered as a unique environment with characteristic pH, oxygen concentration, and microbiome. Given the well-established arsenic redox transformation activities of microorganisms, it is reasonable to imagine how the GIT microbiome composition variability among individuals could play a significant role in determining the fate, mobility and toxicity of arsenic, whether inhaled or ingested. This is a relatively new field of research that would benefit from early dialogue aimed at summarizing what is known and identifying reasonable research targets and concepts. Herein, we strive to initiate this dialogue by reviewing known aspects of microbe-arsenic interactions and placing it in the context of potential for influencing host exposure and health risks. We finish by considering future experimental approaches that might be of value.

'There's antimony, arsenic, aluminum, selenium, and hydrogen, and oxygen, and nitrogen and rhenium'-so begins 'The Elements' song (https://www.youtube.com/watch?v=AcS3NOQnsQM), whereby Tom Lehrer (Fig. 1) assiduously deconstructed the many painstaking decades of research effort by scores of scientists in assembling the Periodic Table as primarily based upon the atomic numbers of the elements. Lehrer instead opted for his imaginative rhyme, with its musical meter purloined from the patter song of Major General Stanley ("I am the Very Model of a Modern Major General') as in the Gilbert and Sullivan's operetta 'The Pirates of Penzance'. By some coincidence, however, three of the four named in the first stanza are Group 15 and 16 elements with which I have considerable microbiological research experience. Only one is missing (tellurium). Hence, by futzing with Lehrer's 'libretto' to suit my own needs for this issue of FEMS, I would pose the following introductory re-rearrangement: 'There's antimony, arsenic, selenium, tellurium, and cadmium, and chromium, and calcium and curium'. While this may (or may not) sit well with Mr Lehrer, who at the time of this writing is still living, I hope it does not cause further discomfiture to the collective eternal peace of Professor Dimitri Mendeleev, Sir William Schwenk Gilbert and Sir Arthur Sullivan. Nonetheless, I will use this preface to take departure for the primary subject of this manuscript, namely our efforts on selenium, which is where it all got started.

Asking a microbiologist to nominate a favorite microorganism as an example of life they think likely to be encountered beyond Earth, is by definition an exercise in personal bias. Yet it is also perhaps a necessary thing to do when we contemplate what type of terrestrial microorganism could prove adaptable to the environmental rigors encountered on an alien orb. There are practical reasons as well. Planetary protection is a consideration in the context of how clean a lander need be to avoid the mistake of inserting our own microbes onto the planet's surface. Pitfalls, however remote, would include generating false positives, or even seeding the planet with one of our own adaptive microbes, thereby initiating an unwanted runaway exercise in planetary eco-transformation. Yet sterilizing a spacecraft is very expensive. In this context, I recall being part of a small panel, chaired by the late Chuck Klein (NASA), to tackle the question of just how clean a spacecraft need be to land on Mars without generating such problems. After a couple of days of running around the central unanswered question of whether or not our terrestrial microbes could survive on Mars, he threw up his hands and asked “What would happen if I placed a cubic meter of fresh horse manure onto the Martian surface?” The panel members kept silent, until I finally raised my hand and answered: “I can't say anything about the survival of the critters in the manure, but I will state positively that if you can convince Congress to fund such a mission, I would be the first astronaut to proudly step into that pile.” The question remains unanswered to this day.

Mononuclear molybdoenzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyze a number of reactions essential to the carbon, nitrogen, sulfur, arsenic, and selenium biogeochemical cycles. These enzymes are also ancient, with many lineages likely predating the divergence of the last universal common ancestor into the Bacteria and Archaea domains. We have constructed rooted phylogenies for over 1,550 representatives of the DMSOR family using maximum likelihood methods to investigate the evolution of the arsenic biogeochemical cycle. The phylogenetic analysis provides compelling evidence that formylmethanofuran dehydrogenase B subunits, which catalyze the reduction of CO2 to formate during hydrogenotrophic methanogenesis, constitutes the most ancient lineage. Our analysis also provides robust support for selenocysteine as the ancestral ligand for the Mo/W atom. Finally, we demonstrate that anaerobic arsenite oxidase and respiratory arsenate reductase catalytic subunits represent a more ancient lineage of DMSORs compared to aerobic arsenite oxidase catalytic subunits, which evolved from the assimilatory nitrate reductase lineage. This provides substantial support for an active arsenic biogeochemical cycle on the anoxic Archean Earth. Our work emphasizes that the use of chalcophilic elements as substrates as well as the Mo/W ligand in DMSORs has indelibly shaped the diversification of these enzymes through deep time.

Primary production in Mono Lake, a hypersaline soda lake rich in dissolved inorganic arsenic, is dominated by Picocystis strain ML. We set out to determine if this photoautotrophic picoplankter could metabolize inorganic arsenic and in doing so form unusual arsenolipids (e.g., arsenic bound to 2-O-methyl ribosides) as reported in other saline ecosystems and by halophilic algae. We cultivated Picocystis strain ML on a seawater-based medium with either low (37 µM) or high (1000 µM) phosphate in the presence of arsenite (400 µM), arsenate (800 µM), or without arsenic additions (ca 0.025 µM). Cultivars formed a variety of organoarsenic compounds, including a phytyl 2-O-methyl arsenosugar, depending upon the cultivation conditions and arsenic exposure. When the cells were grown at low P, the organoarsenicals they produced when exposed to both arsenite and arsenate were primarily arsenolipids (~88%) with only a modest content of water-soluble organoarsenic compounds (e.g., arsenosugars). When grown at high P, sequestration shifted to primarily water-soluble, simple methylated arsenicals such as dimethylarsinate; arsenolipids still constituted ~32% of organoarsenic incorporated into cells exposed to arsenate but < 1% when exposed to arsenite. Curiously, Picocystis strain ML grown at low P and exposed to arsenate sequestered huge amounts of arsenic into the cells accounting for 13.3% of the dry biomass; cells grown at low P and arsenite exposure sequestered much lower amounts, equivalent to 0.35% of dry biomass. Extraction of a resistant phase with trifluoroacetate recovered most of the sequestered arsenic in the form of arsenate. Uptake of arsenate into low P-cultivated cells was confirmed by X-ray fluorescence, while XANES/EXAFS spectra indicated the sequestered arsenic was retained as an inorganic iron precipitate, similar to scorodite, rather than as an As-containing macromolecule. Samples from Mono Lake demonstrated the presence of a wide variety of organoarsenic compounds, including arsenosugar phospholipids, most prevalent in zooplankton (Artemia) and phytoplankton samples, with much lower amounts detected in the bottom sediments. These observations suggest a trophic transfer of organoarsenicals from the phytoplankton (Picocystis) to the zooplankton (Artemia) community, with efficient bacterial mineralization of any lysis-released organoarsenicals back to inorganic oxyanions before they sink to the sediments.

Earth system science is boundless. There are no limits to the kinds of questions, problems, mysteries, or paradoxes that motivate our research and shape its direction. So how do we decide which directions to take, which questions to answer, what problems to solve? Sometimes our research is motivated by an unanticipated event requiring a degree of stochastic interpretive crystal ball gazing. Last year we ended our careers of more than four decades as life scientists at the USGS in Menlo Park, CA. We find ourselves in a state of reflection and want to share a story about a stochastic event that brought us together as collaborators, taught us essential lessons of life as research scientists, and seeded a friendship that endures.

The microscopic alga Picocystis sp. strain ML is responsible for recurrent algal blooms in Mono Lake, CA. This organism was characterized by only very little molecular data, despite its prominence as a primary producer in saline environments. Here, we report the draft genome sequence for Picocystis sp. strain ML based on long-read sequencing.

The marine and environmental microbiology science communities lost one of its star players, Ron Kiene, at the untimely age of 59. Ron passed away from complications associated with battling a squamous cell carcinoma, first diagnosed in 2016. The cancer had metastasized, but he only learned of it after returning from a research cruise in 2018. He underwent a debilitating course of further surgery, radiation, and chemotherapy treatments in late 2018 and early 2019, all while still teaching his course load. Ron was always a powerful, heads-on fighter, never one to quit, but the cumulative treatments proved too harsh even for him to bear. He succumbed to heart failure during the night of 19 January 2019. Ron was born on 06 July 1959 in the city of New York, the borough of Brooklyn, the neighborhood of Bay Ridge. He arrived a year after the beloved Dodgers departed for LA, the same year in which construction of the Verrazano Narrows Bridge began, which when completed in 1964 bisected Bay Ridge. To those who grew up in those southern reaches of Brooklyn by the sea like Bay Ridge or Coney Island, two things were “in the blood” so to speak: baseball and fishing. The loss of the Dodgers (dem Bums) was particularly galling to the denizens of Bay Ridge because many of the players, in those years before free agency and outrageous salaries, dwelt among the hoi polloi. The arrival of the Mets in 1962 only rubbed salt into the open wound, as until 1969 they were horrible, and moreover the Mets settled into Shea Stadium in Queens rather than Brooklyn. Something had to be done to rectify the borough's lost glory, perhaps someday by one of Bay Ridge's native sons? The southern reaches of Brooklyn border the Atlantic Ocean via the New York Bight and its estuarine extensions, like Jamaica Bay and the lower Hudson River. While the rest of the city swelters in summer, these regions are cooled by onshore sea breezes. The salt air that wafts ashore beckons young boys to the littoral for adventures in the exploration of tidal life, swimming in summer, and of course watching the fishermen make their casts. As one grew older, shoreline fishing become a pastime, and Ron started indulging this nascent passion along stretches of Shore (Belt Parkway) Boulevard than circumscribed his neighborhood. When older and more adventurous, there were party boats to be had from nearby Sheepshead Bay that would venture further out to sea for catching giant fluke, porgies, mackerel, cod, stripers, and bluefish. This was the milieu (baseball and fishing) into which Ron grew up and was well ensconced in by the time he entered public high school. And it was not just any city high school: it was Stuyvesant High in lower Manhattan, a free prep school for the city's gifted, competitive kids. You had to be smart just to get in, and very smart to get out 4 yr later with your diploma in hand. Mixed in with his academics, came spring Ron played baseball for “Stuy” and became their starting pitcher. So much so that the Dodgers drafted him after graduation, and a future in Los Angeles beckoned, but he balked. Maybe it had something to do with an inkling of shoulder issues arising as a harbinger of a short career in the majors, or maybe it had something to do with feeling a traitor to Brooklyn and deserting the memory of “dem Bums” for the frivolities of the west coast's LA-LA land, but he chose a cerebral path instead. He went to college at St. John's University in Queens, where he continued to pitch on a baseball scholarship, and the team heading twice to the nationwide College World Series over the 4 yr he matriculated (and pitched). To get into the CWS is a big deal, and to give you an idea of what the quality of his team was like, two other pitchers on St. John's at the time were Frank Viola and John Franco, both of whom headed to the major leagues. Ron graduated with a B.S. in biology in 1981, but by then his shoulder truly ached and he gave up the idea of major league baseball. After all, he could always fall back on his second passion: fishing! Well, sort of…….Ron's initial interest was zoological, dealing with marine sediment invertebrate in-fauna like worms and clams (aka: live bait), but this changed when he arrived at SUNY Stony Brook's Marine Science Research Center (MSRC) and tied in with his mentor, Doug Capone. Doug steered him toward sediment microbiology, focusing on methanogenesis and sulfate reduction. Ron's passion and enthusiasm for science was unleashed and unbridled during graduate school. During his graduate tenure at MSRC, Ron insisted (against his advisor's advice) to obtain his M.S. degree along the way. His rationale was to show his parents and grandparents that he was making progress. An early indication of Ron's potential was the awarding of a regular NSF grant from the Ocean Sciences/Biological Oceanography research section to fund his Ph.D. research. Three of the present writers (RO, GK, and DC) remember fondly gathering on a very blizzardy February day in 1985 for Ron's qualifying exam at Stony Brook. The event was coincident with the arrival of Doug's second daughter, adding to the chaos of the weather for Ron's first major academic hurdle (which he sailed over). He also found time to mentor his mentors, for example, infecting Doug with his love of the music of Mark Knopfler and Dire Straits. Bill Dennison at UMCES/Horn Point, then a Postdoctoral Fellow at Stony Brook, remembers Ron's pitching prowess: “I very much enjoyed playing catch with Ron behind the Discovery building at MSRC. He could throw a curve ball that I found difficult to catch and a fastball (with his left arm) that I could catch, but it left my hand stinging. Ron would have me hold a glove in front of me with two hands as a target and invariably he would hit the target. He was impressive. I also recall introducing Ron to a chemist friend from MIT when Ron was still a graduate student and he said that his demeanor completely changed when the subject switched from chemistry to baseball. Ron was tentative with him about chemistry, but his confidence noticeably increased when talking about baseball. I loved picking Ron's brain when I would see him a meetings, as he was such a good synthesizer and explainer. He could distill hotly debated topics into understandable bits.” A brief sojourn at Ron Oremland's lab in California got him interested in dimethyl sulfide (DMS) as a precursor substrate for methanogenesis, and from thence he never looked back. He finished his Ph.D. in 1986, and while working in Capone's lab, met one of Doug's master's students (Julie McDaniel) whom he wed in 1987. From the MSRC they headed south to Rosenstiel School of Marine & Atmospheric Sciences (RSMAS) of the University of Miami, where he worked with Barrie F. Taylor (mentor to Oremland and Capone) also tying in while there with Pieter Visscher (who had first worked with Ron at MSRC), another Taylor postdoc. As a bona fide member of the “Miami Mafia” Ron delved into microbial metabolism of the DMS precursor, dimethyl-sulfoniopropionate (DMSP). From there, a faculty position opened up at the University of Georgia's Marine Institute. In February of 1988, Ron and Julie moved to the offshore wilderness of Sapelo Island and lived in the shadow of the R.J. Reynold estate. Ron continued work on Spartina but expanded his research to include volatile sulfur in estuarine and coastal waters and even microbial mats. Days in Sapelo were either spent in the lab or when the moon and tide were favorable, on a road bike loaded with fishing rods, cast nets and buckets, its narrow tires digging into the beach under the heavy load. With shrimp or fresh caught fish on the table, dolphins in the surf, and sea turtles laying eggs on the beach, Sapelo offered an opposite world of Brooklyn and Miami for Ron and Julie. This also meant that hurricanes found the island in their path. A nervous father-to-be, Ron had to evacuate Julie during category five storm Hugo, just days before Andrew Devon was born on 01 October 1989. Exciting times persisted, especially when Ron attempted to relocate a big reptile from his property to keep young Andrew out of harm's way, finding out first hand that even a small gator tail can whip ferociously. A few years later, in December 1992, the Kienes, moved to Mobile, AL, where Ron took a faculty position at the University of South Alabama (USA) and its Dauphin Island Sea Lab (DISL) where his lab was located. A little over a year later, Julie and Ron's second son Dylan was born; both Andrew (Physics professor at Nova Southeastern) and Dylan (Ph.D. candidate in Fisheries) followed in Ron's science footsteps, but Dylan is the one who got Ron's baseball and fishing genes. During Ron's 26-yr career at U.S.A. and DISL, he touched many. Upon his arrival, Ron immediately made an impact on the research culture at the lab, which until that point was mainly focused on marine ecology and fisheries. In his first graduate Chemical Oceanography class, he introduced the course as the “ecology of elements in the ocean.” This is indeed how Ron looked at the world as a connected Earth system from macro to microscales. He hooked many of us on this way of thinking, and his generosity with his knowledge and skills allowed us to follow in his footsteps. Ron was a dedicated mentor to the younger faculty who began their careers at DISL and who looked up to Ron for advice in navigating the tenure process and establishing their labs. Ron's effectiveness as a mentor was born out of his child-like curiosity about the natural world. This was infectious for both students and colleagues. Brief exchanges of niceties at the coffee pot often turned into long and in depth dissections of some topic that he had been mulling over or of some problem of your own that piqued his interest. These conversations would often lead to proposals or pilot studies to flesh out ideas and methods. As important were the conversations about his boys' recent successes or the latest political outrage, as we loved Ron's passion for making the world a better place and how proud he was of his family. Ron was clearly the most accomplished member of the DISL faculty, and his outstanding research brought students and postdocs from all over the world to work in his lab and learn from him. Gelling discussions with Maureen Keller and Pieter Visscher, Ron started organizing the First International Symposium on DMSP and Related Onium Compounds shortly after arriving in Alabama. In early June of 1995, 64 scientists from 12 countries gathered for a week in Mobile to discuss the present and future of odorous sulfur compounds. A year later, Ron et al. published a 400-page book on DMSP, with contributions of most of the prominent organosulfur researchers. The breadth of topics covered in this 36-chapter publication is further evidence for Ron's impact on the field and interest in virtually all aspects of sulfur biochemistry and microbiology. A recent article details the impact Ron work had on the organosulfur biogeochemical research community (Boden 2019). Ron won the most important awards at U.S.A. for his scholarship and was widely recognized for his many successes and accomplishments at his home institutions, as well as nationally and internationally. Ron taught Chemical Oceanography to many students who went on to their own distinguished careers, and it is fair to say that Ron was a success in everything he attempted during his long and productive career at U.S.A. and DISL. In 2015, Ron was made a Fellow of the Association for the Sciences of Limnology and Oceanography. Ron's prowess on the baseball diamond is well known. He anchored the U.S.A./DISL intramural softball team that competed in the league for many seasons. Ron's abilities were far above everyone else but he cheerfully played with his amateur teammates. Ironically, at the very first game that Ron participated in, not knowing that he was such a talented athlete and mainly going by his laid-back appearance as a young chemical oceanographer, Ron was positioned in right field thinking that was the place where he would do the least harm. He turned in a stellar game in the field and at the plate and thereafter Ron patrolled the outfield at most games because his ability to chase down balls and quickly throw them back to the infield was beyond compare. In one memorable game, a particularly well-hit ball was flagged down by Ron near the outfield fence and he quickly turned and threw the ball on a straight line all the way from the fence to home plate. Unfortunately, our catcher was inexperienced and not looking for the missile Ron had sent his way. Just as he turned in Ron's direction, the ball struck him in the chest with a sickening thump. The catcher slowly fell over backward and lay still. Everyone on the field rushed to him, thinking he might be unconscious or even worse. He was conscious, but badly shaken and he had the clear imprint of a softball on his chest in what was becoming a huge bruise. We helped him off the field and sat him down to rest. But he never returned to play another game after that encounter with Ron's throwing arm. Because he was so passionate about science, Ron loathed antiscientific politics and policies especially regarding global warming and associated changes. He was an ardent supporter of activism to support and bolster the scientific enterprise. He was active in the March for Science and regularly voiced his concerns and opinions as a scientist in op-ed pieces for the local Mobile, AL newspaper. He could be a very tough critic of both ideas and people, but his criticism was tempered with thoughtful and constructive feedback. As a friend and colleague, he was one of a kind and irreplaceable. We shall miss the days of research, play, fishing, laughing about the ones that got away, and planning the next adventure. Much has been said and written about Ron's scientific accomplishments, his athletic prowess, and his passion for fishing. During his all too short lifetime, he packed enough success in each of these realms to fill the lives of numerous others. Yet even though he will long be remembered for his discoveries, his baseball championships, and the big ones that did not get away, it is the successes in his personal life that arguably mattered the most and will be remembered the longest. What always stood out about Ron in all of his endeavors were his modesty, humility, patience, and compassion. Those who worked with him experienced those traits often. They were an ideal complement to his drive, his focus, his competitiveness, and his desire for perfection. In all that he did, Ron set the bars for success high, and he worked very hard to clear them, even though he made it seem effortless. Yet he worked equally hard to help others clear their own bars. Remarkably, he did so with a generous and selfless spirit, not expecting a quid pro quo for his efforts, but understanding that contributing to the successes of others meant building a bigger and better team for all. Thus, as much as his colleagues and students applauded his scientific acumen, they paid even greater tribute to his humanity. Perhaps it is as fitting to think of him as the highly regarded Coach Ron as it is to think of him as the much admired Professor Kiene. Outside of the walls of academe, Ron was also a coach, both literally and figuratively, again with much success. But he was a listener and learner as well, who built strong, nurturing, and lasting relationships with his beloved wife, Julie, and his two sons, Andrew and Dylan, of whom he was “button bustin’” proud, and bragged often. Julie and the “boys” carry on now with plans to create a summer home in Alaska, the focus of Ron's retirement dreams. Yet they are not merely following in Ron's footsteps or trying to imitate him. Ron's gift was providing both examples of good life choices and the space in which to make them or not. Ron lives on then through his family and the many he influenced, who seek to create good lives in their own way for themselves and others, with his memory as a firm foundation. He would be very pleased. A Research Scholarship is being established in Ron's name at the University of South Alabama memory (https://giving.southalabama.edu/kiene, active August 2019). All donations will be matched 1:1 from the Moulton–Mitchell Fund at the University of South Alabama. We thank William Dennison (UMCES), Ken Heck, John Lehrter, and Kelly Dorgan (DISL) for their contributions to this article.

The putative respiratory selenite [Se(IV)] reductase (Srr) from Bacillus selenitireducens MLS10 has been identified through a polyphasic approach involving genomics, proteomics, and enzymology. Nondenaturing gel assays were used to identify Srr in cell fractions, and the active band was shown to contain a single protein of 80 kDa. The protein was identified through liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a homolog of the catalytic subunit of polysulfide reductase (PsrA). It was found to be encoded as part of an operon that contains six genes that we designated srrE, srrA, srrB, srrC, srrD, and srrF. SrrA is the catalytic subunit (80 kDa), with a twin-arginine translocation (TAT) leader sequence indicative of a periplasmic protein and one putative 4Fe-4S binding site. SrrB is a small subunit (17 kDa) with four putative 4Fe-4S binding sites, SrrC (43 kDa) is an anchoring subunit, and SrrD (24 kDa) is a chaperon protein. Both SrrE (38 kDa) and SrrF (45 kDa) were annotated as rhodanese domain-containing proteins. Phylogenetic analysis revealed that SrrA belonged to the PsrA/PhsA clade but that it did not define a distinct subgroup, based on the putative homologs that were subsequently identified from other known selenite-respiring bacteria (e.g., Desulfurispirillum indicum and Pyrobaculum aerophilum). The enzyme appeared to be specific for Se(IV), showing no activity with selenate, arsenate, or thiosulfate, with a K-m of 145 +/- 53 mu M, a V-max of 23 +/- 2.5 mu M min(-1), and a k(cat) of 23 +/- 2.68 s(-1). These results further our understanding of the mechanisms of selenium biotransformation and its biogeochemical cycle. IMPORTANCE Selenium is an essential element for life, with Se(IV) reduction a key step in its biogeochemical cycle. This report identifies for the first time a dissimilatory Se(IV) reductase, Srr, from a known selenite-respiring bacterium, the haloalkalophilic Bacillus selenitireducens strain MLS10. The work extends the versatility of the complex iron-sulfur molybdoenzyme (CISM) superfamily in electron transfer involving chalcogen substrates with different redox potentials. Further, it underscores the importance of biochemical and enzymological approaches in establishing the functionality of these enzymes.

Elementary tellurium is currently of great interest as an element with potential promise in nano-technology applications because of the recent discovery regarding its three two-dimensional phases and the existence of Weyl nodes around its Femi level. Here, we report on the unique nano-photonic properties of elemental tellurium particles [Te(0)], as harvest from a culture of a tellurium-oxyanion respiring bacteria. The bacterially-formed nano-crystals prove effective in the photonic applications tested compared to the chemically-formed nano-materials, suggesting a unique and environmentally friendly route of synthesis. Nonlinear optical measurements of this material reveal the strong saturable absorption and nonlinear optical extinctions induced by Mie scattering over broad temporal and wavelength ranges. In both cases, Te-nanoparticles exhibit superior optical nonlinearity compared to graphene. We demonstrate that biological tellurium can be used for a variety of photonic applications which include their proof-of-concept for employment as ultrafast mode-lockers and all-optical switches.

Abstract Hal.ar.se.na.ti.bac ' ter. Gr. n. hals, halos, salt, N.L. n. arsenas, ‐atis , arsenate, N.L. masc. n. bacter , rod; N.L. masc. n. Halarsenatibacter , the salty, arsenate‐respiring rod. Firmicutes / Clostridia / Halanaerobiales / Halanaerobiaceae / Halarsenatibacter The genus Halarsenatibacter is classified into the family Halanaerobiaceae , order Halanaerobiales, and in the class Clostridia . Currently, a single species, H. silvermanii , has been described. This haloalkaliphilic, motile bacterium stains Gram‐negative and is shaped as a slightly curved rod. H. silvermanii is an obligate anaerobe that uses arsenate, Fe(III), or elemental sulfur as electron acceptors for chemoheterotrophic growth with electron donors such as lactate, pyruvate, malate, and sugars such as galactose, sucrose, and fructose. Fermentative growth was not observed. Chemoautotrophic growth occurs with sulfide as the electron donor and arsenate as the electron acceptor, but cells lack RubisCO activity as the means for CO 2 fixation. The major membrane fatty acids included saturated branched (46%), unsaturated branched (10%), normal saturated (32.5%), and normal unsaturated (11.2%) fatty acids as detailed in Switzer Blum et al. (2009a). DNA G + C content ( mol% ): 42.5 as analyzed by HPLC by the DSM. Type species : Halarsenatibacter silvermanii Switzer Blum, Han, Lanoil, Saltikov, Witte, Tabita et al., 2009b, 1985 VP (Effective publication: Switzer Blum, Han, Lanoil, Saltikov, Witte, Tabita et al., 2009a, 1959).

Citrobacter sp. strain TSA-1 is an enteric bacterium isolated from the hindgut of the termite. Strain TSA-1 displays anaerobic growth with selenite, fumarate, tetrathionate, nitrate, or arsenate serving as electron acceptors, and it also grows aerobically. In regards to arsenate, genome sequencing revealed that strain TSA-1 lacks a homolog for respiratory arsenate reductase, arrAB, and we were unable to obtain amplicons of arrA. This raises the question as to how strain TSA-1 achieves As(V)-dependent growth. We show that growth of strain TSA-1 on glycerol, which it cannot ferment, is linked to the electron acceptor arsenate. A series of transcriptomic experiments were conducted to discern which genes were upregulated during growth on arsenate, as opposed to those on fumarate or oxygen. For As(V), upregulation was noted for 1 of the 2 annotated arsC genes, while there was no clear upregulation for tetrathionate reductase (ttr), suggesting that this enzyme is not an alternative to arrAB as occurs in certain hyperthermophilic archaea. A gene-deletion mutant strain of TSA-1 deficient in arsC could not achieve anaerobic respiratory growth on As(V). Our results suggest that Citrobacter sp. strain TSA-1 has an unusual and as yet undefined means of achieving arsenate respiration, perhaps involving its ArsC as a respiratory reductase as well as a detoxifying agent.

Acetylene (IUPAC name: ethyne) is a colorless, gaseous hydrocarbon, composed of two triple bonded carbon atoms attached to hydrogens (C2H2). When microbiologists and biogeochemists think of acetylene, they immediately think of its use as an inhibitory compound of certain microbial processes and a tracer for nitrogen fixation. However, what is less widely known is that anaerobic and aerobic microorganisms can degrade acetylene, using it as a sole carbon and energy source and providing the basis of a microbial food web. Here, we review what is known about acetylene degrading organisms and introduce the term 'acetylenotrophs' to refer to the microorganisms that carry out this metabolic pathway. In addition, we review the known environmental sources of acetylene and postulate the presence of an hidden acetylene cycle. The abundance of bacteria capable of using acetylene and other alkynes as an energy and carbon source suggests that there are energy cycles present in the environment that are driven by acetylene and alkyne production and consumption that are isolated from atmospheric exchange. Acetylenotrophs may have developed to leverage the relatively high concentrations of acetylene in the pre-Cambrian atmosphere, evolving later to survive in specialized niches where acetylene and other alkynes were produced.

Algal blooms in lakes are often associated with anthropogenic eutrophication; however, they can occur without the human introduction of nutrients to a lake. A rare bloom of the alga Picocystis sp. strain ML occurred in the spring of 2016 at Mono Lake, a hyperalkaline lake in California, which was also at the apex of a multiyear-long drought. These conditions presented a unique sampling opportunity to investigate microbiological dynamics and potential metabolic function during an intense natural algal bloom. We conducted a comprehensive molecular analysis along a depth transect near the center of the lake from the surface to a depth of 25 m in June 2016. Across sampled depths, rRNA gene sequencing revealed that Picocystis-associated chloroplasts were found at 40 to 50% relative abundance, greater than values recorded previously. Despite high relative abundances of the photosynthetic oxygenic algal genus Picocystis, oxygen declined below detectable limits below a depth of 15 m, corresponding with an increase in microorganisms known to be anaerobic. In contrast to previously sampled years, both metagenomic and metatranscriptomic data suggested a depletion of anaerobic sulfate-reducing microorganisms throughout the lake's water column. Transcripts associated with photosystem I and II were expressed at both 2 m and 25 m, suggesting that limited oxygen production could occur at extremely low light levels at depth within the lake. Blooms of Picocystis appear to correspond with a loss of microbial activity such as sulfate reduction within Mono Lake, yet microorganisms may survive within the sediment to repopulate the lake water column as the bloom subsides.IMPORTANCE Mono Lake, California, provides a habitat to a unique ecological community that is heavily stressed due to recent human water diversions and a period of extended drought. To date, no baseline information exists from Mono Lake to understand how the microbial community responds to human-influenced drought or algal bloom or what metabolisms are lost in the water column as a consequence of such environmental pressures. While previously identified anaerobic members of the microbial community disappear from the water column during drought and bloom, sediment samples suggest that these microorganisms survive at the lake bottom or in the subsurface. Thus, the sediments may represent a type of seed bank that could restore the microbial community as a bloom subsides. Our work sheds light on the potential photosynthetic activity of the halotolerant alga Picocystis sp. strain ML and how the function and activity of the remainder of the microbial community responds during a bloom at Mono Lake.