N-glyceroyl alkylamine phosphoglycolipids dominate the lipidome of several Bacillota bacteria

Elucidation of the membrane lipid composition of bacteria can help to better understand how bacterial cells interact with their surroundings, adapt to environmental stress, and resist antimicrobial agents. Here we describe for the first time the detection of a wide array of N-glyceroyl alkylamine phosphoglycolipids (NGAPs) in a range of Bacillota bacteria (formerly Firmicutes). Bacillota includes a diverse range of bacteria that are typically highly resistant to harsh conditions such as heat, radiation, and pH, allowing the bacteria to survive in unfavorable environments. In 9 out 18 investigated strains of Bacillota, spread across 5 orders (Thermoanaerobacterales, Thermosediminibacterales, Eubacteriales, Halanaerobiales, and Sulfobacillia) mild acid hydrolysis released N-glyceroyl alkylamines (NGAs), which were detectable by gas chromatography-mass spectrometry (GC-MS) during routine fatty acid analysis. One strain, Moorella thermoacetica was found to produce long-chain NGAs (C30-C32), which are postulated to have isodiabolic acid-like structures. A wide variety of intact polar NGAPs were identified using ultra-high pressure liquid chromatography high resolution multi-stage mass spectrometry (UHPLC-HRMSn). These include many previously undescribed lipids with a variety of sugar moieties and glycerol-bound core lipid moieties, including ether-bound components and alkyl 1,2-diols. The NGAPs constituted the majority of the intact polar lipid composition of these strains and presumably contribute to their tough cell membranes. The presence of NGAs in Bacillota appears to be associated with thermophilia. Both the hydrolysis-derived NGAs and intact polar NGAPs have potential to be biomarkers for extremophilic and, in particular, thermophilic bacteria.

Unveiling the impact of microplastics with distinct polymer types and concentrations on tidal sediment microbiome and nitrogen cycling

Microplastics (MPs) are distributed widely in the ocean surface waters and sediments. Increasing MPs contamination in intertidal zone profoundly impacts microbial ecosystem services and biogeochemical process. Little is known about the response of tidal sediment microbiome to MPs. We conducted a 30-day laboratory microcosm study using five polymers (PE, PBS, PC, PLA and PET) at three concentrations (1 %, 2 % and 5 %, w/w). High throughput sequencing of 16 S rRNA, qPCR and enzyme activity test were applied to demonstrate the response of microbial community and nitrogen cycling functional genes to MPs. MPs reduced the microbial alpha diversity and the microbial dissimilarity while the effects of PLA-MPs were concentration dependent. LEfSe analysis indicated that the Proteobacteria predominated for all MP treatments. Mantel's test, RDA and correlation analysis implied that pH may be the key environmental factor for causing microbial alterations. MPs enhanced nitrogen fixation in tidal sediment. PLA levels of 1 % but not 5 % produced the most significant effects in nitrogen cycling functional microbiota and genes. PLS-PM revealed that impacts of MPs on tidal sediment microbial communities and nitrogen cycling were dominated by indirect effects. Our study deepened understanding and filled the knowledge gap of MP contaminants affecting tidal sediment microbial nitrogen cycling.

Hyperthermophilic endospores germinate and metabolize organic carbon in sediments heated to 80°C

Cold surface sediments host a seedbank of functionally diverse thermophilic bacteria. These thermophiles are present as endospores, which are widely dispersed in aquatic environments. Here, we investigated the functional potential of endospore populations in cold surface sediments heated to 80°C. Microbial production of acetate was observed at 80°C and could be enhanced by supplying additional organic carbon substrates. Comparison of 16S rRNA gene amplicon libraries from 80°C enrichments to sediments heated to lower temperatures (50-70°C) showed that temperature selects for distinct populations of endospore-forming bacteria. Whereas sulfate-reducing thermophiles were enriched in 50-70°C incubations, 80°C exceeds their thermal tolerance and selects for hyperthermophilic organotrophic bacteria that are similarly detected in amplicon libraries from sediments heated to 90°C. Genome-resolved metagenomics revealed novel carbon cycling members of Symbiobacteriales, Thermosediminibacteraceae, Thermanaeromonas and Calditerricola with the genomic potential for the degradation of carbohydrates, sugars, amino acids and nucleotides. Endospores of thermophilic bacteria are deposited on seabed sediments worldwide where they remain dormant as they are buried in the accumulating sediments. Our results suggest that endospore populations could be activated by temperature increases encountered during burial and show the potential for organotrophic metabolic activity contributing to acetate generation in deep hot sediments.

Koleobacter methoxysyntrophicus gen. nov., sp. nov., a novel anaerobic bacterium isolated from deep subsurface oil field and proposal of Koleobacteraceae fam. nov. and Koleobacterales ord. nov. within the class Clostridia of the phylum Firmicutes

An anaerobic thermophilic, rod-shaped bacterium possessing a unique non-lipid sheathed-like structure enveloping a single-membraned cell, designated strain NRmbB1^T was isolated from at the deep subsurface oil field located in Yamagata Prefecture, Japan. Growth occurred with 40-60°C (optimum, 55°C), 0-2% (2%), NaCl and pH 6.0-8.5 (8.0). Fermentative growth with various sugars was observed. Glucose-grown cells generated acetate, hydrogen, pyruvate and lactate as the main end products. Syntrophic growth occurred with glucose, pyruvate and 3,4,5-trimethoxybenzoate in the presence of an H₂-scavenging partner, and growth on 3,4,5-trimethoxybenzoate was only observed under syntrophic condition. The predominant cellular fatty acids were C_16:0, iso-C_16:0, anteiso-C_15:0, and iso-C_14:0. Respiratory quinone was not detected. The genomic G+C content was 40.8mol%. Based on 16S rRNA gene phylogeny, strain NRmbB1^T belongs to a distinct order-level clade in the class Clostridia of the phylum Firmicutes, sharing low similarity with other isolated organisms (i.e., 87.5% for top hit Moorella thermoacetica DSM 2955^T). In total, chemotaxonomic, phylogenetic and genomic characterization revealed that strain NRmbB1^T (=KCTC 25035^T, =JCM 39120^T) represents a novel species of a new genus. In addition, we also propose the associated family and order as Koleobacteraceae fam. nov and Koleobacterales ord. nov., respectively.

A flavin-based extracellular electron transfer mechanism in diverse Gram-positive bacteria

Extracellular electron transfer (EET) describes microbial bioelectrochemical processes in which electrons are transferred from the cytosol to the exterior of the cell1. Mineral-respiring bacteria use elaborate haem-based electron transfer mechanisms2-4 but the existence and mechanistic basis of other EETs remain largely unknown. Here we show that the food-borne pathogen Listeria monocytogenes uses a distinctive flavin-based EET mechanism to deliver electrons to iron or an electrode. By performing a forward genetic screen to identify L. monocytogenes mutants with diminished extracellular ferric iron reductase activity, we identified an eight-gene locus that is responsible for EET. This locus encodes a specialized NADH dehydrogenase that segregates EET from aerobic respiration by channelling electrons to a discrete membrane-localized quinone pool. Other proteins facilitate the assembly of an abundant extracellular flavoprotein that, in conjunction with free-molecule flavin shuttles, mediates electron transfer to extracellular acceptors. This system thus establishes a simple electron conduit that is compatible with the single-membrane structure of the Gram-positive cell. Activation of EET supports growth on non-fermentable carbon sources, and an EET mutant exhibited a competitive defect within the mouse gastrointestinal tract. Orthologues of the genes responsible for EET are present in hundreds of species across the Firmicutes phylum, including multiple pathogens and commensal members of the intestinal microbiota, and correlate with EET activity in assayed strains. These findings suggest a greater prevalence of EET-based growth capabilities and establish a previously underappreciated relevance for electrogenic bacteria across diverse environments, including host-associated microbial communities and infectious disease.

Propionate metabolism and diversity of relevant functional genes by in silico analysis and detection in subsurface petroleum reservoirs

Propionate is a common metabolic intermediate occurring in environmental samples including petroleum reservoirs. Available microbial genomes were obtained from the NCBI database and analyzed in silico by hmmscan to check three metabolic pathways of propionate production in petroleum reservoir systems. The succinate pathway was the dominant one while the other two (lactate and 1,2-propanediol pathways) contributed less to the formation of propionate according to the Hidden Markov Model calculation. The mmdA gene encoding methylmalonyl-CoA decarboxylase was used as a biomarker gene to detect the diversity of microbes involved in the propionate formation in Jiangsu oil reservoirs. The mmdA gene clone library showed that microbes affiliated within the genus of Archaeoglobus, Thermococcus, Anaerobaculum, as well as more than ten other genera were the potential microorganisms involved in the production of propionate. Meanwhile, as the biomarker genes involved in the other two propionate-producing pathways, the functional genes of lcdA and pduP were tested with PCR amplification, but no positive results were observed in Jiangsu oil reservoirs.

Thermovenabulum gondwanense sp. nov., a thermophilic anaerobic Fe(III)-reducing bacterium isolated from microbial mats thriving in a Great Artesian Basin bore runoff channel

A strictly anaerobic, thermophilic bacterium, designated strain R270T, was isolated from microbial mats thriving in the thermal waters (66 °C) of a Great Artesian Basin bore (registered no. 17263) runoff channel. Cells of strain R270T were straight to slightly curved rods (3.50–6.00×0.75–1.00 μm) that stained Gram-positive, but possessed a Gram-negative cell-wall ultrastructure. Strain R270T grew optimally in tryptone-yeast extract-Casamino acids medium at 65 °C (growth temperature range between 50 and 70 °C) and at pH 7.0 (growth pH range between 6.0 and 9.0). In the presence of 0.02 and 0.10 % yeast extract, pyruvate and Casamino acids were the only substrates fermented from a wide spectrum of substrates tested. Fe(III), Mn(IV), thiosulfate and elemental sulfur were used as electron acceptors in the presence 0.2 % yeast extract, but not sulfate, sulfite, nitrate, nitrite or fumarate. Growth of strain R270T increased in the presence of Fe(III), which was reduced in the presence of peptone, tryptone, Casamino acids, amyl media, starch, pyruvate, H2 and CO2, but not in the presence of acetate, lactate, propionate, formate, benzoate, glycerol or ethanol. Growth and Fe(III) reduction were inhibited by chloramphenicol, streptomycin, tetracycline, penicillin, ampicillin and 2 % NaCl (w/v). The DNA G+C content of strain R270T was 41±1 mol% (T m) and phylogenetic analysis of the 16S rRNA gene indicated that this isolate was closely related to Thermovenabulum ferriorganovorum DSM 14006T (similarity value of 96.1 %) within the family ‘Thermoanaerobacteraceae’, class ‘Clostridia’, phylum ‘Firmicutes’. On the basis of the phylogenetic distance separating the two, together with differences in a number of key phenotypic characteristics, strain R270T represents a novel species of the genus Thermovenabulum, for which the name Thermovenabulum gondwanense sp. nov. is proposed; the type strain is R270T (=KCTC 5616T=DSM 21133T).

Fervidicella metallireducens gen. nov., sp. nov., a thermophilic, anaerobic bacterium from geothermal waters

A strictly anaerobic, thermophilic bacterium, designated strain AeB(T), was isolated from microbial mats colonizing a run-off channel formed by free-flowing thermal water from a bore well (registered number 17263) of the Great Artesian Basin, Australia. Cells of strain AeB(T) were slightly curved rods (2.5-6.0x1.0 mum) that stained Gram-negative and formed spherical terminal to subterminal spores. The strain grew optimally in tryptone-yeast extract-Casamino acids medium at 50 degrees C (range 37-55 degrees C) and pH 7 (range pH 5-9). Strain AeB(T) grew poorly on yeast extract (0.2 %) and tryptone (0.2 %) as sole carbon sources, which were obligately required for growth on other energy sources. Growth of strain AeB(T) increased in the presence of various carbohydrates and amino acids, but not organic acids. End products detected from glucose fermentation were ethanol, acetate, CO2 and H2. In the presence of 0.2 % yeast extract, iron(III), manganese(IV), vanadium(V) and cobalt(III) were reduced, but not sulfate, thiosulfate, sulfite, elemental sulfur, nitrate or nitrite. Iron(III) was also reduced in the presence of tryptone, peptone, Casamino acids and amyl media (Research Achievement), but not starch, xylan, chitin, glycerol, ethanol, pyruvate, benzoate, lactate, acetate, propionate, succinate, glycine, serine, lysine, threonine, arginine, glutamate, valine, leucine, histidine, alanine, aspartate, isoleucine or methionine. Growth was inhibited by chloramphenicol, streptomycin, tetracycline, penicillin, ampicillin and NaCl concentrations >2 %. The DNA G+C content was 35.4+/-1 mol%, as determined by the thermal denaturation method. 16S rRNA gene sequence analysis indicated that strain AeB(T) is a member of the family Clostridiaceae, class Clostridia, phylum 'Firmicutes', and is positioned approximately equidistantly between the genera Sarcina, Anaerobacter, Caloramator and Clostridium (16S rRNA gene similarity values of 87.8-90.9 %). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain AeB(T) is considered to represent a novel species in a new genus, for which the name Fervidicella metallireducens gen. nov., sp. nov. is proposed; the type strain is AeB(T) (=JCM 15555(T)=KCTC 5667(T)).