Eubacterium aggreganssp. nov., a New Homoacetogenic Bacterium from Olive Mill Wastewater Treatment Digestor

Electron bifurcation and fluoride efflux systems implicated in defluorination of perfluorinated unsaturated carboxylic acids by Acetobacterium spp

Enzymatic cleavage of C─F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. The microbial defluorination products were structurally confirmed and showed regiospecificity and stereospecificity, consistent with their formation by enzymatic reactions. A comparison of defluorination activities among several Acetobacterium species indicated that a functional fluoride exporter was required for the detoxification of the released fluoride. Results from both in vivo inhibition tests and in silico enzyme modeling suggested the involvement of enzymes of the flavin-based electron-bifurcating caffeate reduction pathway [caffeoyl-CoA reductase (CarABCDE)] in the reductive defluorination. This is a report on specific microorganisms carrying out enzymatic reductive defluorination of PFAS, which could be linked to electron-bifurcating reductases that are environmentally widespread.

Microbiome dynamics and products profiles of biowaste fermentation under different organic loads and additives

Biowaste fermentation is a promising technology for low-carbon print bioenergy and biochemical production. Although it is believed that the microbiome determines both the fermentation efficiency and the product profiles of biowastes, the explicit mechanisms of how microbial activity controls fermentation processes remained to be unexplored. The current study investigated the microbiome dynamics and fermentation product profiles of biowaste fermentation under different organic loads (5, 20, and 40 g-VS/L) and with additives that potentially modulate the fermentation process via methanogenesis inhibition (2-bromoethanesulfonate) or electron transfer promotion (i.e., reduced iron, magnetite iron, and activated carbon). The overall fermentation products yields were 440, 373 and 208 CH4-eq/g-VS for low-, medium- and high-load fermentation. For low- and medium-load fermentation, volatile fatty acids (VFAs) were first accumulated and were gradually converted to methane. For high-load fermentation, VFAs were the main fermentation products during the entire fermentation period, accounting for 62% of all products. 16S rRNA-based analyses showed that both 2-bromoethanesulfonate addition and increase of organic loads inhibited the activity of methanogens and promoted the activity of distinct VFA-producing bacterial microbiomes. Moreover, the addition of activated carbon promoted the activity of H2-producing Bacteroides, homoacetogenic Eubacteriaceae and methanogenic Methanosarcinaceae, whose activity dynamics during the fermentation led to changes in acetate and methane production. The current results unveiled mechanisms of microbiome activity dynamics shaping the biowaste fermentation product profiles and provided the fundamental basis for the development of microbiome-guided engineering approaches to modulate biowaste fermentation toward high-value product recovery.

Acetogen and acetogenesis for biological syngas valorization

The bioconversion of syngas using (homo)acetogens as biocatalysts shows promise as a viable option due to its higher selectivity and milder reaction conditions compared to thermochemical conversion. The current bioconversion process operates primarily to produce C2 chemicals (e.g., acetate and ethanol) with sufficient technology readiness levels (TRLs) in process engineering (as midstream) and product purification (as downstream). However, the economic feasibility of this process could be improved with greater biocatalytic options in the upstream phase. This review focuses on the Wood-Ljungdahl pathway (WLP) which is a biological syngas-utilization pathway, redox balance and ATP generation, suggesting that the use of a specific biocatalysts including Eubacterium limosum could be advantageous in syngas valorization. A pertinent strategy to mainly produce chemicals with a high degree of reduction is also provided with examples of flux control, mixed cultivation and mixotrophy. Finally, this article presents future direction of industrial utilization of syngas fermentation.

Competitive Reactions during Ethanol Chain Elongation Were Temporarily Suppressed by Increasing Hydrogen Partial Pressure through Methanogenesis Inhibition

Organic waste streams can be converted into high-value platform chemicals such as medium-chain carboxylic acids (MCCAs) using mixed microbial communities via chain elongation. However, the heterogeneity of waste streams and the use of complex microbial communities can lead to undesirable reactions, thus decreasing process efficiency. We explored suppressing excessive ethanol oxidation to acetate (EEO) by increasing the hydrogen partial pressure (PH2) through hydrogenotrophic methanogenesis inhibition by periodically adding 2-bromoethanesulfonate (2-BES) to an MCCA-producing bioreactor to reach 10 mM of 2-BES upon addition. The bioreactor was fed with pretreated food waste and brewery waste containing high concentrations of short-chain carboxylic acids and ethanol, respectively. While 2-BES addition initially reduced EEO, some methanogens (Methanobrevibacter spp.) persisted and resistant populations were selected over time. Besides changing the methanogenic community structure, adding 2-BES also changed the bacterial community structure due to its impact on PH2. While we demonstrated that PH2 could be manipulated using 2-BES to control EEO, methods that do not require the addition of a chemical inhibitor should be explored to maintain optimum PH2 for long-term suppression of EEO.

Mixotrophic chain elongation with syngas and lactate as electron donors

Feeding microbial communities with both organic and inorganic substrates can improve sustainability and feasibility of chain elongation processes. Sustainably produced H2 , CO2 , and CO can be co-fed to microorganisms as a source for acetyl-CoA, while a small amount of an ATP-generating organic substrate helps overcome the kinetic hindrances associated with autotrophic carboxylate production. Here, we operated two semi-continuous bioreactor systems with continuous recirculation of H2 , CO2 , and CO while co-feeding an organic model feedstock (lactate and acetate) to understand how a mixotrophic community is shaped during carboxylate production. Contrary to the assumption that H2 , CO2 , and CO support chain elongation via ethanol production in open cultures, significant correlations (p < 0.01) indicated that relatives of Clostridium luticellarii and Eubacterium aggregans produced carboxylates (acetate to n-caproate) while consuming H2 , CO2 , CO, and lactate themselves. After 100 days, the enriched community was dominated by these two bacteria coexisting in cyclic dynamics shaped by the CO partial pressure. Homoacetogenesis was strongest when the acetate concentration was low (3.2 g L-1 ), while heterotrophs had the following roles: Pseudoramibacter, Oscillibacter, and Colidextribacter contributed to n-caproate production and Clostridium tyrobutyricum and Acidipropionibacterium spp. grew opportunistically producing n-butyrate and propionate, respectively. The mixotrophic chain elongation community was more efficient in carboxylate production compared with the heterotrophic one and maintained average carbon fixation rates between 0.088 and 1.4 g CO2 equivalents L-1  days-1 . The extra H2 and CO consumed routed 82% more electrons to carboxylates and 50% more electrons to carboxylates longer than acetate. This study shows for the first time long-term, stable production of short- and medium-chain carboxylates with a mixotrophic community.

Leveraging substrate flexibility and product selectivity of acetogens in two-stage systems for chemical production

Carbon dioxide (CO2 ) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H2 -dependent CO2 gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state-of-the-art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double-stage biotechnological production processes that use CO2 as sole carbon feedstock and H2 as energy carrier for products' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products' spectrum. Alternatively, when the first stage is abiotic, the integrated two-stage scheme foresees, in the first stage, the catalytic transformation of CO2 into C1 products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO2 abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production.

Methanol and methyl group conversion in acetogenic bacteria: biochemistry, physiology and application

The production of bulk chemicals mostly depends on exhausting petroleum sources and leads to emission of greenhouse gases. Within the last decades the urgent need for alternative sources has increased and the development of bio-based processes received new attention. To avoid the competition between the use of sugars as food or fuel, other feedstocks with high availability and low cost are needed, which brought acetogenic bacteria into focus. This group of anaerobic organisms uses mixtures of CO2, CO and H2 for the production of mostly acetate and ethanol. Also methanol, a cheap and abundant bulk chemical produced from methane, is a suitable substrate for acetogenic bacteria. In methylotrophic acetogens the methyl group is transferred to the Wood-Ljungdahl pathway, a pathway to reduce CO2 to acetate via a series of C1-intermediates bound to tetrahydrofolic acid. Here we describe the biochemistry and bioenergetics of methanol conversion in the biotechnologically interesting group of anaerobic, acetogenic bacteria. Further, the bioenergetics of biochemical production from methanol is discussed.

Formate metabolism in the acetogenic bacterium Acetobacterium woodii

Acetogenic bacteria are already established as biocatalysts for production of high-value compounds from C1 substrates such as H₂  + CO₂ or CO. However, little is known about the physiology, biochemistry and bioenergetics of acetogenesis from formate, an interesting feedstock for biorefineries. Here, we analysed formate metabolism in the model acetogen Acetobacterium woodii. Cells grew optimally on 200 mM formate to an optical density of 0.6. Formate was exclusively converted to acetate (and CO₂ ) with a ratio of 4.4:1. Transcriptome analyses revealed genes/enzymes involved in formate metabolism. Strikingly, A. woodii has two genes potentially encoding a formyl-THF synthetase, fhs1 and fhs2. fhs2 forms an operon with a gene encoding a potential formate transporter, fdhC. Deletion of fhs2/fdhC led to a reduced growth rate, formate consumption and optical densities. Acetogenesis from H₂  + CO₂ was accompanied by transient formate production; strikingly, formate reutilization was completely abolished in the Δfhs2/fdhC mutant. Take together, our studies gave the first detailed insights into the formatotrophic lifestyle of A. woodii.

Production of high-calorific biogas from food waste by integrating two approaches: Autogenerative high-pressure and hydrogen injection

Auto-generative high pressure digestion (AHPD) and hydrogen-injecting digestion (HID) have been introduced to directly produce high CH₄-content biogas from anaerobic digester. However, each approach has its own technical difficulties (pH changes), and practical issues (high cost of H₂) to obtain > 90% CH₄ containing biogas, particularly, from the high-strength waste like food waste (FW). To overcome this problem, in this study, AHPD and HID were integrated, which can offset each drawback but maximize its benefit. Substrate concentration of FW tested here was 200 g COD/L, the highest ever applied in AHPD and HID studies. At first, the reactor was operated by elevating the autogenerative pressure from 1 to 3, 5, and 7 bar without H₂ injection. With the pressure increase, the CH₄ content in the biogas gradually increased from 52.4% at 1 bar to 77.4% at 7 bar. However, a drop of CH₄ production yield (MPY) was observed at 7 bar, due to the pH drop down to 6.7 by excess CO₂ dissolution. At further operation, H₂ injection began at 5 bar, with increasing its amount. The injection was effective to increase the CH₄ content to 82.8%, 87.2%, and 90.6% at 0.09, 0.13, and 0.18 L H₂/g COD_FW.fed of H₂ injection amount, respectively. At 0.25 L H₂/g COD_FW.fed, there was a further increase of CH₄ content to 92.1%, but the MPY was dropped with pH increase to 8.7 with residual H₂ being detected (4% in the biogas). Microbial community analysis showed the increased abundance of piezo-tolerant microbe with pressure increase, and direct interspecies electron transfer contributors after H₂ injection. In conclusion, the integration of two approaches enabled to directly produce high calorific biogas (90% > CH₄, 180 MJ/m³ biogas) from high-strength FW at the lowest requirement of H₂ (0.18 L H₂/g COD_FW.fed) ever reported.

Unravelling lactate-acetate and sugar conversion into butyrate by intestinal Anaerobutyricum and Anaerostipes species by comparative proteogenomics

The d- and l-forms of lactate are important fermentation metabolites produced by intestinal bacteria but are found to negatively affect mucosal barrier function and human health. Both enantiomers of lactate can be converted with acetate into the presumed beneficial butyrate by a phylogenetically related group of anaerobes, including Anaerobutyricum and Anaerostipes spp. This is a low energy yielding process with a partially unknown pathway in Anaerobutyricum and Anaerostipes spp. and hence, we sought to address this via a comparative genomics, proteomics and physiology approach. We compared growth of Anaerobutyricum soehngenii on lactate with that on sucrose and sorbitol. Comparative proteomics revealed complete pathway of butyrate formation from sucrose, sorbitol and lactate. Notably, a gene cluster, lctABCDEF was abundantly expressed when grown on lactate. This gene cluster encodes a lactate dehydrogenase (lctD), electron transport proteins A and B (lctCB), nickel-dependent racemase (lctE), lactate permease (lctF) and short-chain acyl-CoA dehydrogenase (lctG). Investigation of available genomes of intestinal bacteria revealed this new gene cluster to be highly conserved in only Anaerobutyricum and Anaerostipes spp. Present study demonstrates that A. soehngenii and several related Anaerobutyricum and Anaerostipes spp. are highly adapted for a lifestyle involving lactate plus acetate utilization in the human intestinal tract.

Using gas mixtures of CO, CO2 and H2 as microbial substrates: the do's and don'ts of successful technology transfer from laboratory to production scale

The reduction of CO2 emissions is a global effort which is not only supported by the society and politicians but also by the industry. Chemical producers worldwide follow the strategic goal to reduce CO2 emissions by replacing existing fossil-based production routes with sustainable alternatives. The smart use of CO and CO2 /H2 mixtures even allows to produce important chemical building blocks consuming the said gases as substrates in carboxydotrophic fermentations with acetogenic bacteria. However, existing industrial infrastructure and market demands impose constraints on microbes, bioprocesses and products that require careful consideration to ensure technical and economic success. The mini review provides scientific and industrial facets finally to enable the successful implementation of gas fermentation technologies in the industrial scale.

Bacterial Anaerobic Synthesis Gas (Syngas) and CO2+H2 Fermentation

Anaerobic bacterial gas fermentation gains broad interest in various scientific, social, and industrial fields. This microbial process is carried out by a specific group of bacterial strains called acetogens. All these strains employ the Wood-Ljungdahl pathway but they belong to different taxonomic groups. Here we provide an overview of the metabolism of acetogens and naturally occurring products. Characteristics of 61 strains were summarized and selected acetogens described in detail. Acetobacterium woodii, Clostridium ljungdahlii, and Moorella thermoacetica serve as model organisms. Results of approaches such as genome-scale modeling, proteomics, and transcriptomics are discussed. Metabolic engineering of acetogens can be used to expand the product portfolio to platform chemicals and to study different aspects of cell physiology. Moreover, the fermentation of gases requires specific reactor configurations and the development of the respective technology, which can be used for an industrial application. Even though the overall process will have a positive effect on climate, since waste and greenhouse gases could be converted into commodity chemicals, some legislative barriers exist, which hamper successful exploitation of this technology.

Comparative reaction engineering analysis of different acetogenic bacteria for gas fermentation

The production of chemicals by syngas fermentation is a promising alternative to heterotrophic fermentation processes. The autotrophic process performances of the so far not well studied acetogens Acetobacterium fimetarium, Acetobacterium wieringae, Blautia hydrogenotrophica, Clostridium magnum, Eubacterium aggregans, Sporomusa acidovorans, Sporomusa ovata and Terrisporobacter mayombei were characterized. Acetobacterium woodii was used as reference strain. Standardized batch experiments with continuous supply of the gaseous substrates CO2 and H2 were performed in fully controlled stirred-tank bioreactors. A. wieringae and S. ovata showed by far the highest growth rates and maximum biomass concentrations among the acetogens under study. Aside from the reference strain A. woodii, highest volumetric (17.96gL(-1)d(-1)) as well as cell specific acetate formation rates (21.03gg(-1)d(-1)) were observed with S. ovata resulting in a final acetate concentration of 32.2gL(-1). Accumulation of formate with up to 4.8gL(-1) was observed with all acetogens. Ethanol was produced autotrophically with up to 0.42gL(-1) by four of the acetogenic bacteria under study (A. wieringae, C. magnum, S. acidovorans and S. ovata) and also by A. woodii. Butyrate was formed with up to 0.14gL(-1) by three of the acetogenic bacteria under study (C. magnum, B. hydrogenotrophica and E. aggregans). Due to its superior process performances S. ovata may be a promising host for redirecting carbon fluxes by applying metabolic engineering and tools of synthetic biology to produce non-natural chemicals from syngas.

Genome sequence of Clostridium tunisiense TJ, isolated from drain sediment from a pesticide factory

Clostridium tunisiense is a Gram-positive, obligate anaerobe that was first isolated in an anaerobic environment under eutrophication. Here we report the first genome sequence of the Clostridium tunisiense TJ isolated from drain sediment of a pesticide factory in Tianjin, China. The genome is of great importance for both basic and application research.

Syntrophic interactions drive the hydrogen production from glucose at low temperature in microbial electrolysis cells

H(2) can be obtained from glucose by fermentation at mesophilic temperatures, but here we demonstrate that hydrogen can also be obtained from glucose at low temperatures using microbial electrolysis cells (MECs). H(2) was produced from glucose at 4°C in single-chamber MECs at a yield of about 6 mol H(2)mol(-1) glucose, and at rates of 0.25±0.03-0.37±0.04 m(3) H(2)m(-3)d(-1). Pyrosequencing of 16S rRNA gene and electrochemical analyses showed that syntrophic interactions combining glucose fermentation with the oxidization of fermentation products by exoelectrogens was the predominant pathway for current production at a low temperature other than direct glucose oxidization by exoelectrogens. Another syntrophic interaction, methanogenesis and homoacetogenesis, which have been found in 25°C reactors, were not detected in MECs at 4°C. These results demonstrate the feasibility of H(2) production from abundant biomass of carbohydrates at low temperature in MECs.

Pathway engineering and synthetic biology using acetogens

Acetogenic anaerobic bacteria are defined as organisms employing the Wood-Ljungdahl pathway to synthesize acetyl-CoA from CO(2) or CO. Their autotrophic mode of metabolism offers the biotechnological chance to combine use of abundantly available substrates with reduction of greenhouse gases. Several companies have already established pilot and demonstration plants for converting waste gases into ethanol, an important biofuel and a natural product of many acetogens. Recombinant DNA approaches now opened the door to construct acetogens, synthesizing important industrial bulk chemicals and biofuels such as acetone and butanol. Thus, novel microbial production platforms are available that no longer compete with nutritional feedstocks.

Alkalibaculum bacchi gen. nov., sp. nov., a CO-oxidizing, ethanol-producing acetogen isolated from livestock-impacted soil

Phenotypic and phylogenetic studies were performed on three strains of an acetogenic bacterium isolated from livestock-impacted soil. The bacterium stained Gram-negative and was a non-spore-forming rod that was motile by peritrichous flagella. The novel strains had an optimum pH for growth of 8.0–8.5 and utilized H2 : CO2, CO : CO2, glucose, fructose, mannose, turanose, ribose, trimethylamine, pyruvate, methanol, ethanol, n-propanol and n-butanol as growth substrates. Acetate was produced from glucose. Acetate, CO2 and ethanol were produced from CO : CO2. 16S rRNA gene sequence analysis indicated that the novel strains formed a new subline in the family Eubacteriaceae (rRNA cluster XV) of the low G+C-containing Gram-positive bacteria of the class Clostridia. The DNA G+C base composition was 34 mol%. Cell wall analysis revealed the existence of a novel B-type peptidoglycan similar to the B2α-type (B4) configuration with a variation containing aspartic acid. Based on phylogenetic and phenotypic evidence, it is proposed that the new isolates represent a novel genus and species, for which the name Alkalibaculum bacchi gen. nov., sp. nov. is proposed. The type strain of the type species is CP11T (=ATCC BAA-1772T=DSM 22112T).

Old acetogens, new light

Acetogens utilize the acetyl-CoA Wood-Ljungdahl pathway as a terminal electron-accepting, energy-conserving, CO(2)-fixing process. The decades of research to resolve the enzymology of this pathway (1) preceded studies demonstrating that acetogens not only harbor a novel CO(2)-fixing pathway, but are also ecologically important, and (2) overshadowed the novel microbiological discoveries of acetogens and acetogenesis. The first acetogen to be isolated, Clostridium aceticum, was reported by Klaas Tammo Wieringa in 1936, but was subsequently lost. The second acetogen to be isolated, Clostridium thermoaceticum, was isolated by Francis Ephraim Fontaine and co-workers in 1942. C. thermoaceticum became the most extensively studied acetogen and was used to resolve the enzymology of the acetyl-CoA pathway in the laboratories of Harland Goff Wood and Lars Gerhard Ljungdahl. Although acetogenesis initially intrigued few scientists, this novel process fostered several scientific milestones, including the first (14)C-tracer studies in biology and the discovery that tungsten is a biologically active metal. The acetyl-CoA pathway is now recognized as a fundamental component of the global carbon cycle and essential to the metabolic potentials of many different prokaryotes. The acetyl-CoA pathway and variants thereof appear to be important to primary production in certain habitats and may have been the first autotrophic process on earth and important to the evolution of life. The purpose of this article is to (1) pay tribute to those who discovered acetogens and acetogenesis, and to those who resolved the acetyl-CoA pathway, and (2) highlight the ecology and physiology of acetogens within the framework of their scientific roots.

NMR bioreactor development for live in-situ microbial functional analysis

A live, in-situ metabolomics capability was developed for prokaryotic cultures under controlled growth conditions. Toward this goal, a radiofrequency-transparent bioreactor was developed and integrated with a commercial wide-bore nuclear magnetic resonance (NMR) imaging spectrometer and a commercial bioreactor controller. Water suppressed 1H NMR spectroscopy was used to monitor glucose and fructose utilization and byproduct excretion by Eubacterium aggregans (an anaerobic bacterial species relevant for biofuel production) under controlled batch and continuous culture conditions. The resulting metabolite profiles (short chain organic acids and ethanol) and trends are consistent with existing knowledge of its metabolism. However, our study also showed that E. aggregans produces lactate end product in significant concentrations-a result not previously reported. The advantages of live in-situ microbial metabolomics analysis and its complementariness with functional genomics/systems biology methods are discussed.

Clostridium tunisiense sp. nov., a new proteolytic, sulfur-reducing bacterium isolated from an olive mill wastewater contaminated by phosphogypse

A new sporulated fermentative bacterium designated strain E1(T) (T=type strain), was isolated from an anaerobic mud of an olive mill wastewater basin contaminated by phosphogypse produced by a Tunisian factory. Strain E1(T) was a motile Gram-positive slightly curved rod with spherical terminal spore swelling the cell. It grew between 18 degrees C and 43 degrees C with an optimum at 37 degrees C and pH 7.8 (range 5.5-8.7), without NaCl (range 0-3%). Strain E1(T) was a chemoorganotrophic anaerobic bacterium fermenting only proteins and amino acids. Yeast extract was required for growth. Elemental sulfur was used as terminal electron acceptor. The G+C content of the DNA was 32.6 mol%. The closest phylogenetical relatives of strain E1(T) were Clostridium thiosulfatireducens and C. subterminale (97.3% similarity for partial rRNA gene sequences). DNA-DNA hybridization values between strain E1(T) and both species were 17% and 20.8%, respectively. On the basis of differences in genotypic and phenotypic characteristics, strain E1(T) (DSM 15206(T), CIP 107666(T)) is proposed as the type strain of a new species, C. tunisiense sp. nov. GenBank accession number for the 16S rRNA gene sequence of strain E1(T) is AY187622.

Anaerobic, alkaliphilic, saccharolytic bacterium Alkalibacter saccharofermentans gen. nov., sp. nov. from a soda lake in the Transbaikal region of Russia

Three strains of new obligately anaerobic alkaliphilic bacteria have been isolated as a saccharolytic component from the cellulolytic community of alkaline Lake Nizhnee Beloe (Transbaikal region, Russia), a lake with low salt concentration. DNA analysis of these strains showed an interspecies level of DNA similarity of 96-100%. Strain Z-79820 was selected for further investigations. Cells were Gram-positive, asporogenous, nonmotile short rods with pointed ends. The strain was a true alkaliphile: growth occurred from pH 7.2 to 10.2 with the optimum at pH 9.0. Strain Z-79820 was halotolerant and could grow in medium with up to 10% (w/v) NaCl, with the optimum between 0 and 4% NaCl. The new isolate obligately depended on Na+ ions in the form of carbonates or chlorides. Total Na+ content needed for optimal growth was 0.46 M Na+, with a wide range from 0.023-0.9 M Na+ at which growth also occurred. The isolate was a mesophile and grew at temperatures from 6 to 50 degrees C (slow growth at 6 and 15 degrees C) with an optimum at 35 degrees C. The organotrophic organism fermented ribose, xylose, glucose, mannose, fructose, sucrose, mannitol, and peptone. The products of glucose fermentation were acetate, ethanol, formate, H2, and CO2. Yeast extract was required for some anabolic needs. The DNA G+C content of the type strain Z-79820 was 42.1 mol%. The new bacterium fell into the 16S rRNA gene cluster XV of the Gram-positive bacteria with low G+C content, where it formed an individual branch. Based on its growth characteristics and genotype traits, we propose the new genus and species named Alkalibacter saccharofermentans with the type strain Z-79820 (=DSM14828), Uniqem-218 (Institute Microbiology, RAS; http://inmi.da.ru).