The specific association of the potentially plant-pathogenic Pseudomonas syringae with Peltigera lichens raises questions about the factors driving this host specificity. To explore this, the metabolic profile of seven lichen species belonging to three genera (Cladonia, Peltigera and Stereocaulon) was analysed using LC-MSMS. In addition, we assessed the growth of P. syringae strains in media supplemented with extracts from each lichen species. This revealed that Peltigera exhibits lower metabolite richness compared to other genera, but shows a higher chemical investment in specific compounds. Growth kinetics showed comparable P. syringae growth across lichen-supplemented media, except for Cladonia arbuscula and Cladonia sp., where the former exhibited lower growth rates. Inhibition assays with lichen extracts showed no inhibition of P. syringae. The lichen metabolome is predominantly composed of lipids and organic acids. Furthermore, specific compounds, such as aminoglycosides, may facilitate P. syringae presence in Peltigera by inhibiting Bacillus subtilis and other antagonists. In addition, compounds absent in Peltigera, like anthracene, might serve as a carbon source inhibitor like Bacillus velezensis.

The presence of bacteria belonging to the Pseudomonas syringae complex in the natural vegetation of several Icelandic habitat types has been recently reported, raising questions about the risk to Icelandic crops, particularly given the expected increase in agricultural activity due to climate warming. This study takes advantage of Iceland's unique characteristics and the discovery of P. syringae in Peltigera lichens to gain a better understanding of the potential risk posed by this newly discovered ecological niche. The main objective was to evaluate the pathogenic potential and fitness in crops of P. syringae strains isolated from Peltigera lichen sampled in Iceland, focusing on strains that belong to phylogroups 1 and 2, which commonly contain epidemic strains. The results indicate that P. syringae strains isolated from Icelandic Peltigera lichen have a comparable fitness to epidemic strains in 8 out of 10 tested plant species (rice, tomato, thale cress, annual mugwort, spinach, garlic chives, tobacco and kale). Furthermore, pathogenicity assessment on three plant species highlighted that certain strains also caused similar symptoms and disease severity compared to epidemic strains. These findings provide valuable insights into the potential risks posed by P. syringae from Icelandic natural habitats and illustrate how strains from these habitats have a wide pathogenic potential to crops without having encountered these crops in the last several thousand years of their presence in Iceland.

Increasing extreme climatic events threaten the functioning of terrestrial ecosystems1,2. Because soil microbes govern key biogeochemical processes, understanding their response to climate extremes is crucial in predicting the consequences for ecosystem functioning3,4. Here we subjected soils from 30 grasslands across Europe to four contrasting extreme climatic events under common controlled conditions (drought, flood, freezing and heat), and compared the response of soil microbial communities and their functioning with those of undisturbed soils. Soil microbiomes exhibited a small, but highly consistent and phylogenetically conserved, response under the imposed extreme events. Heat treatment most strongly impacted soil microbiomes, enhancing dormancy and sporulation genes and decreasing metabolic versatility. Microbiome response to heat in particular could be predicted by local climatic conditions and soil properties, with soils that do not normally experience the extreme conditions being imposed being most vulnerable. Our results suggest that soil microbiomes from different climates share unified responses to extreme climatic events, but that predicting the extent of community change may require knowledge of the local microbiome. These findings advance our understanding of soil microbial responses to extreme events, and provide a first step for making general predictions about the impact of extreme climatic events on soil functioning.

The term ”thermophilic prokaryotes” covers an immense taxonomic and functional diversity of bacteria and archaea, spanning the length and breadth of the prokaryotic Tree of Life. Indeed, thermophiles are found within most major prokaryotic lineages and their functional diversity runs the gamut of biochemical and physiological adaptations. Thus, examples can be found of thermophilic lithoautotrophs as well as chemoheterotrophs, obligate anaerobes and aerophiles, extreme halophiles, acidophiles and alkaliphiles, and more. Their ecology is likewise diverse, with thermophiles found in a variety of habitats ranging from hydrothermal vents to desert soil to industrial settings and wastewater treatment facilities. It goes without saying that such immense diversity cannot be reviewed comprehensively in a relatively short book chapter. We thus aim to present examples pulled from diverse taxa within the vast menagerie of prokaryotic thermophiles in order to give insights into the metabolic, taxonomic, and ecological diversity of thermophilic prokaryotes rather than attempting an exhaustive review.

Pseudomonas syringae is a bacterial complex that is widespread through a range of environments, typically associated with plants where it can be pathogenic, but also found in non-plant environments such as clouds, precipitation, and surface waters. Understanding its distribution within the environment, and the habitats it occupies, is important for examining its evolution and understanding behaviours. After a recent study found P. syringae living among a range of vascular plant species in Iceland, we questioned whether lichens could harbour P. syringae. Sixteen different species of lichens were sampled all over Iceland, but only one lichen genus, Peltigera, was found to consistently harbour P. syringae. Phylogenetic analyses of P. syringae from 10 sampling points where lichen, tracheophyte, and/or moss were simultaneously collected showed significant differences between sampling points, but not between different plants and lichens from the same point. Furthermore, while there were similarities in the P. syringae population in tracheophytes and Peltigera, the densities in Peltigera thalli were lower than in moss and tracheophyte samples. This discovery suggests P. syringae strains can localize and survive in organisms beyond higher plants, and thus reveals opportunities for studying their influence on P. syringae evolution.

Mosses are among the first colonizing organisms after glacier retreat and can develop into thick moss mats during later successional stages. They are key players in N-2 fixation through their microbiome, which is an important process for nutrient buildup during primary succession. How these moss-microbe interactions develop during succession is not well studied and is relevant in the light of climate change and increased glacier retreat. We examined how the bacterial communities associated with two moss species of the genus Racomitrium and the underlying soil, as well as moss traits and nitrogen fixation, develop along a successional gradient in the glacier forefield of Flaajokull in southeast Iceland. In addition, we tested whether moss functional traits, such as total carbon (TC) and total nitrogen (TN) contents, moss moisture content, and moss shoot length are drivers of moss and underlying soil bacterial communities. Although time since deglaciation did not affect TN and moss moisture contents, TC and shoot length increased with time since deglaciation. Moss and underlying soil bacterial communities were distinct. While the soil bacterial community structure was driven by moss C/N ratios, the moss bacterial community structure was linked to time since deglaciation, moss C/N ratio, and moss moisture content. Moss N-2-fixation rates were linked to bacterial community composition and nifH gene abundance rather than moss TN or time since deglaciation. This was accompanied by a shift from autotrophic to heterotrophic diazotrophs. Overall, our results suggest that there is little lateral transfer between moss and soil bacterial communities and that moss traits affect moss and soil bacterial community structure. Only moss bacterial community changed with time since deglaciation. In addition, moss N-2-fixation rates are determined by bacterial community structure, rather than moss traits or time since deglaciation. This study on the interplay between succession, mosses, soils, and their bacterial communities will inform future work on the fate of newly exposed areas as a result of glacier retreat.

Lava tubes on Mars hold exciting potential for the preservation of biosignatures, which may survive on geological timescales in these isolated, stable environments. To support the development of future astrobiological mission concepts, we turn to terrestrial lava tubes, host to a variety of microbial communities and secondary minerals. Following a multidisciplinary sampling protocol, we retrieved biological, molecular, and mineralogical data from several lava tubes in Iceland. We report on blue-colored copper-rich secondary minerals and their associated bacterial communities using a multi-method approach, and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy data sets. We found numerous bacterial genera known for their high metal resistance and ability to survive in low-nutrient environments. Both are characteristics to be expected for any potential life in Martian lava tubes, and should be considered when checking for contaminants in Mars mission preparations. Associated with the microbial mats, we identified several types of copper-rich secondary minerals, indicating localized copper enrichments in the groundwater, possibly stemming from overlying ash deposits and nearby hyaloclastite formations. Molecular analysis revealed carotenoid signals preserved within the copper speleothems. If found in Martian lava tubes, blue copper-rich mineral precipitates would be deserving of astrobiological investigation, as they have potential to preserve biosignatures and harbor life.

Mosses are among the first colonizing organisms after glacier retreat and can develop into thick moss mats during later successional stages. They are key players in N2 fixation through their microbiome, which is an important process for nutrient build-up during primary succession. How these moss-microbe interactions develop during succession is not well-studied and is relevant in the light of climate change and increased glacier retreat. We examined how the bacterial communities associated with two moss species of the genus Racomitrium and the underlying substrate, as well as moss traits and nitrogen fixation, develop along a successional gradient in the glacier forefield of Fláajökull in southeast Iceland. In addition, tested whether moss functional traits, such as total carbon (TC) and nitrogen contents (TN) are drivers of moss and underlying soil bacterial communities. Although time since deglaciation did not affect TN and moisture content, TC and shoot length increased with time since deglaciation. Moss and underlying soil bacterial communities were distinct. While the soil bacterial community structure was driven by the time since deglaciation and moss C/N ratios, the moss bacterial community structure was linked to time since deglaciation and moss moisture content. Moss N2-fixation rates were linked to bacterial community composition and nifH gene abundance rather than moss TN or time since deglaciation. This was accompanied by a shift from autotrophic to heterotrophic diazotrophs. Overall, our results suggest that there is little lateral transfer between moss and soil bacterial communities and that moss traits and time since deglaciation affect moss and soil bacterial community structure. In addition, moss N2-fixation rates are determined by bacterial community structure, rather than moss traits or time since deglaciation.

Bacterial communities form the basis of biogeochemical processes and determine plant growth and health. Mosses harbour diverse bacterial communities that are involved in nitrogen fixation and carbon cycling. Global climate change is causing changes in aboveground plant biomass and shifting species composition in the Arctic, but little is known about the response of moss microbiomes in these environments. Here, we studied the total and potentially active bacterial communities associated with Racomitrium lanuginosum in response to a 20-yr in situ warming in an Icelandic heathland. We evaluated the effect of warming and warming-induced shrub expansion on the moss bacterial community composition and diversity, and nifH gene abundance. Warming changed both the total and the potentially active bacterial community structure, while litter abundance only affected the total bacterial community structure. The abundance of nifH genes was negatively affected by litter abundance. We also found shifts in the potentially nitrogen-fixing community, with Nostoc decreasing and noncyanobacterial diazotrophs increasing in relative abundance. Our data suggest that the moss microbial community and potentially nitrogen fixing taxa will be sensitive to future warming, partly via changes in litter and shrub abundance.

Lava tubes on Mars hold exciting potential for the preservation of biosignatures, which may survive on geological timescales in these isolated, stable environments. To support the development of future astrobiological mission concepts, we turn to terrestrial lava tubes, host to a variety of microbial communities and secondary minerals. Following a multidisciplinary sampling protocol, we retrieved biological, molecular, and mineralogical data from several lava tubes in Iceland. We report on blue‐colored copper‐rich secondary minerals and their associated bacterial communities using a multi‐method approach, and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy data sets. We found numerous bacterial genera known for their high metal resistance and ability to survive in low‐nutrient environments. Both are characteristics to be expected for any potential life in Martian lava tubes, and should be considered when checking for contaminants in Mars mission preparations. Associated with the microbial mats, we identified several types of copper‐rich secondary minerals, indicating localized copper enrichments in the groundwater, possibly stemming from overlying ash deposits and nearby hyaloclastite formations. Molecular analysis revealed carotenoid signals preserved within the copper speleothems. If found in Martian lava tubes, blue copper‐rich mineral precipitates would be deserving of astrobiological investigation, as they have potential to preserve biosignatures and harbor life.

Mosses are among the first colonizing organisms after glacier retreat and can develop into thick moss mats during later successional stages. They are key players in N2 fixation through their microbiome, which is an important process for nutrient build-up during primary succession. How these moss-microbe interactions develop during succession is not well-studied and is relevant in the light of climate change and increased glacier retreat. We examined how the bacterial communities associated with two moss species of the genus Racomitrium and the underlying substrate, as well as moss traits and nitrogen fixation, develop along a successional gradient in the glacier forefield of Fláajökull in southeast Iceland. In addition, tested whether moss functional traits, such as total carbon (TC) and nitrogen contents (TN) are drivers of moss and underlying soil bacterial communities. Although time since deglaciation did not affect TN and moisture content, TC and shoot length increased with time since deglaciation. Moss and underlying soil bacterial communities were distinct. While the soil bacterial community structure was driven by the time since deglaciation and moss C/N ratios, the moss bacterial community structure was linked to time since deglaciation and moss moisture content. Moss N2-fixation rates were linked to bacterial community composition and nifH gene abundance rather than moss TN or time since deglaciation. This was accompanied by a shift from autotrophic to heterotrophic diazotrophs. Overall, our results suggest that there is little lateral transfer between moss and soil bacterial communities and that moss traits and time since deglaciation affect moss and soil bacterial community structure. In addition, moss N2-fixation rates are determined by bacterial community structure, rather than moss traits or time since deglaciation. ### Competing Interest Statement The authors have declared no competing interest.

Within soil, bacteria are found in multispecies communities, where interactions can lead to emergent community properties. Studying bacteria in a social context is critical for investigating community-level functions. We previously showed that cocultured Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 engage in interspecies social spreading (ISS) on a hard agar surface, a behavior which required close contact and depended on the nutritional environment. Here, we investigate whether social spreading is widespread among P. fluorescens and Pedobacter isolates and whether the requirements for interaction vary. We find that this phenotype is not restricted to the interaction between P. fluorescens Pf0-1 and Pedobacter sp. V48 but is a prevalent behavior found in one clade in the P. fluorescens group and two clades in the Pedobacter genus. We show that the interaction with certain Pedobacter isolates occurred without close contact, indicating induction of spreading by a putative diffusible signal. As with ISS by Pf0-1+V48, the motility of interacting pairs is influenced by the environment, with no spreading behaviors (or induction of motility) observed under high nutrient conditions. While Pf0-1+V48 require low nutrient but high NaCl conditions, in the broader range of interacting pairs, the high salt influence was variable. The prevalence of motility phenotypes observed here and found within the literature indicates that community-induced locomotion in general, and social spreading in particular, is likely important within the environment. It is crucial that we continue to study microbial interactions and their emergent properties to gain a fuller understanding of the functions of microbial communities. IMPORTANCE Interspecies social spreading (ISS) is an emergent behavior observed when Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 interact, during which both species move together across a surface. Importantly, this environment does not permit the movement of either individual species. This group behavior suggests that communities of microbes can function in ways not predictable by knowledge of the individual members. Here, we have asked whether ISS is widespread and thus potentially of importance in soil microbial communities. The significance of this research is the demonstration that surface spreading behaviors are not unique to the Pf0-1-V48 interaction but rather is a more widespread phenomenon observed among members of distinct clades of both P. fluorescens and Pedobacter isolates. Furthermore, we identify differences in mechanisms of signaling and nutritional requirements for ISS. Emergent traits resulting from bacterial interactions are widespread, and their characterization is necessary for a complete understanding of microbial community function.

Lichens are traditionally defined as a symbiosis between a fungus and a green alga and or a cyanobacterium. This idea has been challenged by the discovery of bacterial communities inhabiting the lichen thalli. These bacteria are thought to contribute to the survival of lichens under extreme and changing environmental conditions. How these changing environmental conditions affect the lichen-associated bacterial community composition remains unclear. We describe the total (rDNA-based) and potentially metabolically active (rRNA-based) bacterial community of the lichen Cetaria islandica and its response to long-term warming using a 20-year warming experiment in an Icelandic sub-Arctic tundra. 16S rRNA and rDNA amplicon sequencing showed that the orders Acetobacterales (of the class Alphaproteobacteria) and Acidobacteriales (of the phylum Acidobacteria) dominated the bacterial community. Numerous amplicon sequence variants (ASVs) could only be detected in the potentially active community but not in the total community. Long-term warming led to increases in relative abundance of bacterial taxa on class, order and ASV level. Warming altered the relative abundance of ASVs of the most common bacterial genera, such as Granulicella and Endobacter. The potentially metabolically active bacterial community was also more responsive to warming than the total community. Our results suggest that the bacterial community of the lichen C. islandica is dominated by acidophilic taxa and harbors disproportionally active rare taxa. We also show for the first time that climate warming can lead to shifts in lichen-associated bacterial community composition.

Natural gas seepage pockmarks are found off and onshore in the Öxarfjörður graben, NE Iceland. The bacterial communities of two onshore seepage sites were analysed by amplicon sequencing of 16S rDNA, along with determining the geochemical characteristics, hydrocarbon content and the carbon isotope composition of the sites. While one site was found to be characterised by biogenic origin of methane gas, with carbon isotope ratio δ13C [‰] = −63.2, high content of organic matter and complex hydrocarbons, the other site showed a mixed origin of the methane gas (δ13C [‰] = −26.6) with geothermal characteristics and lower organic matter content. While both sites harboured Proteobacteria as the most abundant bacterial phyla, the Deltaproteobacteria were more abundant at the geothermal site, and the Alphaproteobacteria at the biogenic site. The Dehalococcoidia class of the Chloroflexi phylum was abundant at the geothermal site while the Anaerolineae class was more abundant at the biogenic site. Bacterial strains from the seepage pockmarks were isolated on a variety of selective media targeting bacteria with bioremediation potential. A total of 106 strains were isolated and characterised, including representatives from the phyla Proteobacteria, Bacterioidetes, Firmicutes , and Actinobacteria . This article describes the first microbial study on gas seepage pockmarks in Iceland.

AbstractWithin soil, bacteria are naturally found in multi-species communities, where interactions can lead to emergent community properties. It is critical that we study bacteria in a social context to investigate community-level functions. We previously showed that when co-cultured,Pseudomonas fluorescensPf0-1 andPedobactersp. V48 engage in interspecies social spreading on a hard agar surface, a behavior which required close contact and was dependent on the nutritional environment. In this study, we investigate whether the ability to participate in social spreading is widespread amongP. fluorescensandPedobacterisolates, and whether the requirements for interaction vary. We find that this phenotype is not restricted to the interaction betweenP. fluorescensPf0-1 andPedobactersp. V48, but is a more prevalent behavior found in one clade in theP. fluorescensgroup and two clades in thePedobactergenus. We also discovered that the interaction with certainPedobacterisolates occurred without close contact, indicating induction of spreading by a putative diffusible signal. As is the case for ISS by Pf0-1+V48, motility of all interacting pairs is influenced by the environment, with no spreading behaviors observed under high nutrient conditions. While Pf0-1+V48 require low nutrient but high NaCl conditions, in the broader range of interacting pairs this requirement for low nutrient and high salt was variable. The prevalence of motility phenotypes observed in this study and found within the literature indicates that community-induced locomotion in general, and social spreading in particular, is likely important within the environment. It is crucial that we continue to study microbial interactions and their emergent properties to gain a fuller understanding of the functions of microbial communities.

Tomato spotted wilt virus (TSWV) is transmitted by thrips species in a persistent, propagative manner.Frankliniella occidentalis is the most efficient vector, but at least six other thrips species are competent vectors.The TSWV structural glycoprotein (GN) plays an important role in viral attachment and possibly entry into insect host cells.However, the insect molecules that interact with GN during infection and dissemination in thrips vector are still largely unknown.The goals of this study were to characterize TSWV-interacting proteins (TIPs) that interact directly with TSWV GN and to localize expression of these proteins in thrips tissues of importance along the route of virus dissemination.We identified six novel TIPs from first instar larvae (L1) that share homology to proteins associated with the infection cycle of other vector-borne viruses.Two of the thrips proteins, endocuticular structural glycoprotein (endoCP-GN) and cyclophilin, were validated to be consistent interactors with GN in membrane-bound yeast two-hybrid and insect cell co-localization assays.Immunolocalization of these TIPs in L1s revealed robust expression in the midgut and salivary glands of F. occidentalis, the key tissues during viral infection, replication and plant-inoculation.In addition, the homologous endoCP-GN from another thrips vector F. fusca was cloned and validated to interact with TSWV GN.Our findings suggest that the TIPs-GN interaction occurs in vivo and the TSWV GN-endoCP-GN interaction may be conserved among Frankliniella vector species of TSWV.Investigations on the quiescent behavior of Diaporthe ilicicola in deciduous holly fruit I.

1 Bacterial communities form the basis of biogeochemical processes and determine plant 2 growth and health. Mosses, an abundant plant group in Arctic ecosystems, harbour diverse 3 bacterial communities that are involved in nitrogen fixation and carbon cycling. Global 4 climate change is causing changes in aboveground plant biomass and shifting species 5 composition in the Arctic, but little is known about the response of the moss microbiome. 6 Here, we studied the total and potentially active bacterial community associated with 7 Racomitrium lanuginosum, a common moss species in the Arctic, in response to 20-year in 8 situ warming in an Icelandic heathland. We evaluated changes in moss bacterial 9 community composition and diversity. Further, we assessed the consequences of warming 10 for nifH gene copy numbers and nitrogen-fixation rates. Long-term warming significantly 11 changed both the total and the potentially active bacterial community structure. The 12 relative abundance of Proteobacteria increased, while the relative abundance of 13 Cyanobacteria and Acidobacteria decreased. While warming did not affect nitrogen14 fixation rates and nifH gene abundance, we did find shifts in the potentially nitrogen-fixing 15 community, with Nostoc decreasing and non-cyanobacterial diazotrophs increasing in 16 relative abundance. Our data suggests that the moss microbial community and the 17 potentially nitrogen-fixing taxa are sensitive to future warming. 18

FOR UPCOMING MISSIONS IN THE SEARCH FOR EXTANT OR EXTINCT LIFE ON MARS J. M. Csuka, S. Adeli, M. Baqué, I. Iakubivskyi, N. Kopacz, A. Neubeck, A. Schnürer, A. Singh, B. R. Stockwell, O. Vilhelmsson and W. D. Geppert, Department of Biological Sciences, Columbia University, USA, jmc2330@columbia.edu, Institute of Planetary Research, German Aerospace Centre (DLR), Germany, Tartu Observatory, University of Tartu, Estonia, Department of Earth Science, Utrecht University, The Netherlands, Uppsala University, Sweden, Swedish University of Agricultural Sciences, Sweden, Department of Chemistry, Columbia University, USA, University of Akureyri, Iceland, Stockholm University Astrobiology Centre, Sweden.