Ability to reduce insoluble Fe(III) compounds has not been shown for alkaliphilic lithotrophic sulfate and sulfur reducers. Detection of this metabolic process in sulfidogenic prokaryotes could significantly expand the present knowledge on physicochemical range of their growth and physiological activity, which is now limited by low negative ambient redox potential. Capacity for direct reduction of Fe(III) from chemically synthesized ferrihydrite was tested for eight species of hydrogenotrophic haloalkaliphilic sulfidogens grown with formate or H2 as electron donors in the absence of sulfur compounds in the medium. Out of eight tested species, six reduced iron with formate and five, with hydrogen as the electron donor. Iron reduction correlated with stimulation of growth on formate or hydrogen only in two sulfidogenic species. Analysis of available genomes of five tested species revealed that only Dethiobacter alkaliphilus and Desulfuribacillus alkaliarsenatis possess the gene sets of multiheme cytochromes c required for typical dissimilatory iron reduction. The presence of these genes in two strains with high iron-reducing activity indicates the capacity of some haloalkaliphilic sulfidogenic bacteria for carrying out direct dissimilatory reduction of insoluble Fe(III) forms in the absence of sulfur-containing electron acceptors, i.e., without using sulfide as a soluble mediator of iron reduction. In other studied microorganisms, the ability to reduce iron is probably caused by nonspecific metabolic activity and is not directly linked to energy generation for growth, although the rates of Fe(III) reduction determined in our experiments make it possible to suggest significant role of sulfidogenic microorganisms (normally reducing sulfur and sulfate) in the iron cycle in haloalkaline ecosystems upon decreased content of sulfur compounds.

Biogenic transformations of iron-containing minerals synthesized ferrihydrite, magnetite and hydrothermal siderite by anaerobic alkaliphilic bacterium Fuchsiella ferrireducens (strain Z-7101T) were studied by 57Fe Mössbauer spectroscopy. Mössbauer investigations of solid phase samples obtained after microbial transformation were carried out at room temperature and at 82 K. It was found that all tested minerals transformed during bacterial growth. In the presence of synthesized ferrihydrite, added as an electron acceptor, a mixture of large (more than 100 nm) and small (∼5 nm) particles of magnetically ordered phase and siderite was formed. Synthesized magnetite that contains both Fe3+ and Fe2+ forms could serve as electron acceptor as well as an electron donor for F.ferrireducens growth. As a result of its biotransformation, no siderite formation was observed while small particles of magnetite were formed. In the case of the addition of siderite as an electron donor formation of a small amount of a new phase containing Fe2+ caused by recrystallization of siderite during bacterial growth was detected.

Samples of biogenic iron minerals obtained during the growth of the anaerobic alkaliphilic ironreducing bacterium Fuchsiella ferrireducens (strain Ζ-7101Т) in the presence of synthesized ferrihydrite used as electron acceptor are studied by 57Fe Mössbauer spectroscopy. Two series of samples, differing by electron acceptor, are analyzed. Ethanol and acetate are used as electron donors in the first and second series, respectively. Mössbauer studies are performed at room temperature and at 82 K. Phases containing ferrous iron (siderite) form in both series, while a magnetically ordered phase (a mixture of hematite and maghemite particles) forms only in the series with ethanol.

Al.ka.li.bac'ter. Ar. def. art. al the; Ar. n. qaliy ashes of saltwort; N.L. masc. n. bacter (from Gr. n. baktron ) a rod; N.L. masc. n. Alkalibacter alkaliphilic rod. Firmicutes / “Clostridia” / Clostridiales / “Eubacteriaceae” / Alkalibacter Rod‐shaped cells , 0.5 × 1.5–2.5 µm, with Gram‐stain‐positive cell‐wall structure. Nonmotile. Asporogenous. Strictly anaerobic , catalase negative. Obligately alkaliphilic and halotolerant ; growth obligately depends on sodium carbonates or chlorides. Chemoorganoheterotroph ; consumes mono‐ and disaccharides, sugar alcohols, and proteinaceous substrates as energy sources. Glucose is fermented to acetate, ethanol, formate, H 2 , and CO 2 . Requires yeast extract as a possible source of nitrogen and sulfur. Habitats are saline‐carbonate lakes. The genus is monotypic. DNA G + C content ( mol %): 40.8–42.1. Type species : Alkalibacter saccharofermentans Garnova, Zhilina, Tourova, Kostrikina and Zavarzin 2005, 983 VP (Effective publication: Garnova, Zhilina,Tourova, Kostrikina and Zavarzin 2004, 315.).

Ha.lo.na.tro'num. Gr. n. hals, halos salt; Ar. n. natron soda; N.L. neut. n. Halonatronum an organism growing with salt and soda. Firmicutes / “Clostridia” / Halanaerobiales / Halobacteroidaceae / Halonatronum Cells are rod‐shaped , flexible , and motile by peritrichous flagella . The cell wall has a Gram‐stain‐negative structure . Strictly anaerobic . Chemo‐organotrophic with fermentative metabolism. Carbohydrates, including soluble polysaccharides, are fermented to acetate, ethanol, formate, H 2 , and CO 2 . Halophilic and alkaliphilic . Endospores produced . DNA G + C content ( mol %): 34.4 ( T m ). Type species : Halonatronum saccharophilum Zhilina, Garnova, Tourova, Kostrikina and Zavarzin 2001a, 263 VP (Effective publication: Zhilina, Garnova, Tourova, Kostrikina and Zavarzin 2001b, 71.).

Mössbauer studies of bioreduction products stabilized by acetone and ethanol were carried out at wide temperature range from 80 K to room temperature and in external magnetic field applied perpendicular to γ-beam at room temperature. The initial products (mixture of non-stoichiometric magnetite and maghemite) were formed during the iron reduction of synthesized ferrihydrite by bacterium G. ferrihydriticus. The addition of acetone and ethanol led to slight particle size decrease. The average size and magnetic moments were 11.2 nm and 524 µB, respectively.

A mesophilic hydrogenotrophic methanogenic archaeon, strain Z-7105T, was isolated from the bottom sediments of a collector in the vicinity of a soda lake Tanatar II (Altai, Russia). The cells were motile, irregular cocci 0.2–1.2 μm in diameter. The organism was an obligate alkaliphile, growing within a pH range from 8.0 to 10.2, with the optimum at pH 9.0–9.5. It was obligately dependent on carbonates, growing at 0.5 to 1.6 M total carbonates with the optimum at 0.7–0.9 M. Sodium ions were also obligately required at concentrations from 0.9 to 3.3 M Na+ (optimum at 1.4–1.9 M). The organism was halotolerant, but Clions were not required. Hydrogen and formate were used as electron donors. Acetate was required for anabolism. The DNA G+C content was 50.2 mol %. According to the results of its 16S rRNA gene sequence analysis, the isolate belonged to the genus Methanocalculus, being the first known alkaliphilic member of this genus. Its similarity to the neutrophilic and halotolerant Methanocalculus species (M. halotolerans, M. taiwanensis, M. pumilus, and M. chunghsingensis) was 98.2–97.1%, which is within the interspecific range for this genus. The level of DNA-DNA hybridization between strain Z-7105T and the Methanocalculus type species M. halotolerans DSM 14092T was 32%. The genus Methanocalculus, including the new isolate and the previously described species, is distant from other genera of methanogens (<90% 16S rRNA gene similarity). Based on significant phenotypic differences and the results of phylogenetic analysis, including DNA-DNA hybridization, it is proposed to assign strain Z-7105T (=DSM 25006T, =VKM B-2765T) to the new species Methanocalculus natronophilus sp. nov., and to incorporate the genus into the new family Methanocalculaceae fam. nov.

Interaction between a bacterial monoculture of alkaliphylic G. ferrihydriticus along with binary cultures of G. ferrihydriticus and cellulolytic C. alkalicellulosi and natural biotite and glauconite under alkaliphylic conditions is investigated by means of Mössbauer spectroscopy. Measurements were performed over a range of temperatures from T = 4.8 K to T = 300 K. It was found that a new magnetically ordered phase was formed during culture growth. This new phase was a mixture of nonstoichiometric magnetite and maghemite. The relative amount of the magnetically ordered phase in the monoculture of G. ferrihydriticus when interacting with glauconite is less than in the case of the binary culture. Iron reduction glauconite is also more intense than in biotite.

Mossbauer investigations of iron minerals formed during the process of synthesized ferrihydrite (SF) reduction by anaerobic alkaliphilic bacterium Geoalkalibacter ferrihydriticus and anaerobic thermophilic bacterium Thermincola ferriacetica were carried out involving magnetization measurements. The influence of T. ferriacetica and G. ferrihydriticus growth media on SF was investigated. It was found that SF after its interaction with the mineral media was almost identical. There were also analyzed minerals that formed during the growth of binary culture of Geoalkalibacter ferrihydriticus and Anaerobacillus alkalilacustris at the concentrations of SF equal to 10mM. The new phase formed under this concentration is probably of FeII-FeIII (oxy-)hydroxycarbonate nature. Mossbauer spectroscopy showed that in all experiments where magnetically ordered phases formed by dissimilatory iron-reducing bacteria, a mixture of nonstoichiometric magnetite (Fe3O4) and maghemite (gamma-Fe2O3) was observed.

Mössbauer investigations of solid phases that were formed during the reduction of amorphous synthesized ferrihydrite (SF) by thermophilic anaerobic iron-reducing bacterium Thermincola ferriacetica (strain Z-0001) and alkaliphilic anaerobic iron-reducing bacterium Geoalkalibacter ferrihydriticus (strain Z-0531) were carried out at room, liquid nitrogen and helium temperatures in the presence or the absence of an external magnetic field (6 T). The magnetization M (T, H) was measured in the temperature interval 80-300 K and magnetic field up to 10 kOe. It was performed zero field cooling (ZFC) and field cooling (FC) measurements of M (T).

In the course of an investigation of alkaliphilic iron reduction, metabiotic interactions in a binary culture reducing synthetic ferrihydrite (SF) have been studied. The binary culture contained two anaerobic bacteria: the alkaliphilic organotrophic bacillus Anaerobacillus alkalilacustris , which ferments sugars and sugar alcohols and is incapable of iron reduction, and the dissimilatory iron-reducing bacterium Geoalkalibacter ferrihydriticus , which is able to grow on acetate at the expense of anaerobic respiration. The experiments were performed under conditions of SF excess and deficiency. It was expected that G. ferrihydriticus would oxidize the acetate formed in the course of mannitol fermentation by A. alkalilacustris . The results were different from the expected ones: in the binary culture, fermentation products other than acetate were used for iron reduction; these were primarily formate and ethanol, which led to acetate accumulation rather than consumption. The reduction of SF to magnetite and/or siderite followed the earlier established regularities. The preferential order of donor utilization by G. ferrihydriticus did not conform to the energy yields of the corresponding reactions. Thus, it has been shown that there may be interactions in microbial communities that cannot be predicted from the characteristics of pure cultures. The degradation pathways of organic matter in communities may differ considerably from those observed in pure cultures, even in pure cultures of highly specialized organisms.