Complex History of Aerobic Respiration and Phototrophy in the Chloroflexota Class Anaerolineae Revealed by High-Quality Draft Genome of Ca. Roseilinea mizusawaensis AA3_104.

Roseilinea is a novel lineage of Chloroflexota known only from incomplete metagenome-assembled genomes (MAGs) and preliminary enrichments. Roseilinea is notable for appearing capable of anoxygenic photoheterotrophy despite being only distantly related to well-known phototrophs in the Chloroflexia class such as Chloroflexus and Roseiflexus. Here, we present a high-quality MAG of a member of Roseilinea, improving our understanding of the metabolic capacity and phylogeny of this genus, and resolving the multiple instances of horizontal gene transfer that have led to its metabolic potential. These data allow us to propose a candidate family for these organisms, Roseilineaceae, within the Anaerolineae class.

Ecological memory of recurrent drought modifies soil processes via changes in soil microbial community.

Climate change is altering the frequency and severity of drought events. Recent evidence indicates that drought may produce legacy effects on soil microbial communities. However, it is unclear whether precedent drought events lead to ecological memory formation, i.e., the capacity of past events to influence current ecosystem response trajectories. Here, we utilize a long-term field experiment in a mountain grassland in central Austria with an experimental layout comparing 10 years of recurrent drought events to a single drought event and ambient conditions. We show that recurrent droughts increase the dissimilarity of microbial communities compared to control and single drought events, and enhance soil multifunctionality during drought (calculated via measurements of potential enzymatic activities, soil nutrients, microbial biomass stoichiometry and belowground net primary productivity). Our results indicate that soil microbial community composition changes in concert with its functioning, with consequences for soil processes. The formation of ecological memory in soil under recurrent drought may enhance the resilience of ecosystem functioning against future drought events.

Reticulibacter mediterranei gen. nov., sp. nov., within the new family Reticulibacteraceae fam. nov., and Ktedonospora formicarum gen. nov., sp. nov., Ktedonobacter robiniae sp. nov., Dictyobacter formicarum sp. nov. and Dictyobacter arantiisoli sp. nov., belonging to the class Ktedonobacteria.

The aerobic, Gram-positive, mesophilic Ktedonobacteria strains, Uno17T, SOSP1-1T, 1-9T, 1-30T and 150040T, formed mycelia of irregularly branched filaments, produced spores or sporangia, and numerous secondary metabolite biosynthetic gene clusters. The five strains grew at 15-40 °C (optimally at 30 °C) and pH 4.0-8.0 (optimally at pH 6.0-7.0), and had 7.21-12.67 Mb genomes with 49.7-53.7 mol% G+C content. They shared MK9(H2) as the major menaquinone and C16 : 1-2OH and iso-C17 : 0 as the major cellular fatty acids. Phylogenetic and phylogenomic analyses showed that Uno17T and SOSP1-9T were most closely related to members of the genus Dictyobacter, with 94.43-96.21 % 16S rRNA gene similarities and 72.16-81.56% genomic average nucleotide identity. The strain most closely related to SOSP1-1T and SOSP1-30T was Ktedonobacter racemifer SOSP1-21T, with 91.33 and 98.84 % 16S rRNA similarities, and 75.13 and 92.35% average nucleotide identities, respectively. Strain 150040T formed a distinct clade within the order Ktedonobacterales, showing <90.47 % 16S rRNA gene similarity to known species in this order. Based on these results, we propose: strain 150040T as Reticulibacter mediterranei gen. nov., sp. nov. (type strain 150 040T=CGMCC 1.17052T=BCRC 81202T) within the family Reticulibacteraceae fam. nov. in the order Ktedonobacterales; strain SOSP1-1T as Ktedonospora formicarum gen. nov., sp. nov. (type strain SOSP1-1T=CGMCC 1.17205T=BCRC 81203T) and strain SOSP1-30T as Ktedonobacter robiniae sp. nov. (type strain SOSP1-30T=CGMCC 1.17733T=BCRC 81205T) within the family Ktedonobacteraceae; strain Uno17T as Dictyobacter arantiisoli sp. nov. (type strain Uno17T=NBRC 113155T=BCRC 81116T); and strain SOSP1-9T as Dictyobacter formicarum sp. nov. (type strain SOSP1-9T=CGMCC 1.17206T=BCRC 81204T) within the family Dictyobacteraceae.

Metagenomic insights into mixotrophic denitrification facilitated nitrogen removal in a full-scale A2/O wastewater treatment plant.

Wastewater treatment plants (WWTPs) are important for pollutant removal from wastewater, elimination of point discharges of nutrients into the environment and water resource protection. The anaerobic/anoxic/oxic (A2/O) process is widely used in WWTPs for nitrogen removal, but the requirement for additional organics to ensure a suitable nitrogen removal efficiency makes this process costly and energy consuming. In this study, we report mixotrophic denitrification at a low COD (chemical oxygen demand)/TN (total nitrogen) ratio in a full-scale A2/O WWTP with relatively high sulfate in the inlet. Nitrogen and sulfur species analysis in different units of this A2/O WWTP showed that the internal sulfur cycle of sulfate reduction and reoxidation occurred and that the reduced sulfur species might contribute to denitrification. Microbial community analysis revealed that Thiobacillus, an autotrophic sulfur-oxidizing denitrifier, dominated the activated sludge bacterial community. Metagenomics data also supported the potential of sulfur-based denitrification when high levels of denitrification occurred, and sulfur oxidation and sulfate reduction genes coexisted in the activated sludge. Although most of the denitrification genes were affiliated with heterotrophic denitrifiers with high abundance, the narG and napA genes were mainly associated with autotrophic sulfur-oxidizing denitrifiers. The functional genes related to nitrogen removal were actively expressed even in the unit containing relatively highly reduced sulfur species, indicating that the mixotrophic denitrification process in A2/O could overcome not only a shortage of carbon sources but also the inhibition by reduced sulfur of nitrification and denitrification. Our results indicate that a mixotrophic denitrification process could be developed in full-scale WWTPs and reduce the requirement for additional carbon sources, which could endow WWTPs with more flexible and adaptable nitrogen removal.

Metagenomic Analysis Exploring Taxonomic and Functional Diversity of Soil Microbial Communities in Sugarcane Fields Applied with Organic Fertilizer.

Organic fertilizers are critically important to soil fertility, microbial communities, and sustainable agricultural strategies. We compared the effect of two fertilizer groups (organic+chemical fertilizer: OM, chemical fertilizer: CK) on sugarcane growth, by observing the difference in microbial communities and functions, soil nutrient status, and agronomic characters of sugarcane. The results showed that the sugar content and yield of sugarcane increased significantly under organic fertilizer treatment. We believe that the increased soil nutrient status and soil microorganisms are the reasons for this phenomenon. In addition, redundancy analysis (RDA) shows that the soil nutrient condition has a major impact on the soil microbial community. In comparison with CK, the species richness of Acidobacteria, Proteobacteria, Chloroflexi, and Gemmatimonadetes as well as the functional abundance of nucleotide metabolism and energy metabolism increased significantly in the OM field. Moreover, compared with CK, genes related to the absorption and biosynthesis of sulfate were more prominent in OM. Therefore, consecutive organic fertilizer application could be an effective method in reference to sustainable production of sugarcane.

The effect of sulfamonomethoxine treatment on the gut microbiota of Nile tilapia (Oreochromis niloticus).

To investigate the possible effects of sulfamonomethoxine (SMM) on Nile tilapia (Oreochromis niloticus), we quantitatively evaluated the microbial shifts in the intestines of Nile tilapia in response to different doses of SMM (200 and 300 mg/kg) using 16S rRNA gene sequencing. At the phylum level, the control group (0 mg kg-1  SMM) was dominated by Actinobacteria, Proteobacteria, and Firmicutes. In the treatment groups, Firmicutes, Proteobacteria, and Chloroflexi were the dominant phyla. Cluster analysis indicated that the two groups treated with SMM clustered together. Similarly, the bacterial families that dominated the control group differed from those dominating the treatment groups. The changes in intestinal microbial composition over time were similar between the two SMM treatment groups. In both groups, the abundances of some families, including the Bacillaceae, Streptococcaceae, and Pseudomonadaceae, increased first and then decreased. Overall, the addition of SMM to the feed changed the structure of the intestinal microbiota in Nile tilapia. This study improves our understanding of the impact of SMM on the intestinal microenvironment of Nile tilapia. Our results provide guidelines for the feasibility of SMM use in aquaculture production.

Iterative subtractive binning of freshwater chronoseries metagenomes identifies over 400 novel species and their ecologic preferences.

Recent advances in sequencing technology and bioinformatic pipelines have allowed unprecedented access to the genomes of yet-uncultivated microorganisms from diverse environments. However, the catalogue of freshwater genomes remains limited, and most genome recovery attempts in freshwater ecosystems have only targeted specific taxa. Here, we present a genome recovery pipeline incorporating iterative subtractive binning, and apply it to a time series of 100 metagenomic datasets from seven connected lakes and estuaries along the Chattahoochee River (Southeastern USA). Our set of metagenome-assembled genomes (MAGs) represents >400 yet-unnamed genomospecies, substantially increasing the number of high-quality MAGs from freshwater lakes. We propose names for two novel species: 'Candidatus Elulimicrobium humile' ('Ca. Elulimicrobiota', 'Patescibacteria') and 'Candidatus Aquidulcis frankliniae' ('Chloroflexi'). Collectively, our MAGs represented about half of the total microbial community at any sampling point. To evaluate the prevalence of these genomospecies in the chronoseries, we introduce methodologies to estimate relative abundance and habitat preference that control for uneven genome quality and sample representation. We demonstrate high degrees of habitat-specialization and endemicity for most genomospecies in the Chattahoochee lakes. Wider ecological ranges characterized smaller genomes with higher coding densities, indicating an overall advantage of smaller, more compact genomes for cosmopolitan distributions.

Ecological and genomic analyses of candidate phylum WPS-2 bacteria in an unvegetated soil.

Members of the bacterial candidate phylum WPS-2 (or Eremiobacterota) are abundant in several dry, bare soil environments. In a bare soil deposited by an extinct iron-sulfur spring, we found that WPS-2 comprised up to 24% of the bacterial community and up to 108 cells per g of soil based on 16S rRNA gene sequencing and quantification. A single genus-level cluster (Ca. Rubrimentiphilum) predominated in bare soils but was less abundant in adjacent forest. Nearly complete genomes of Ca. Rubrimentiphilum were recovered as single amplified genomes (SAGs) and metagenome-assembled genomes (MAGs). Surprisingly, given the abundance of WPS-2 in bare soils, the genomes did not indicate any capacity for autotrophy, phototrophy, or trace gas metabolism. Instead, they suggest a predominantly aerobic organoheterotrophic lifestyle, perhaps based on scavenging amino acids, nucleotides, and complex oligopeptides, along with lithotrophic capacity on thiosulfate. Network analyses of the entire community showed that some species of Chloroflexi, Actinobacteria, and candidate phylum AD3 (or Dormibacterota) co-occurred with Ca. Rubrimentiphilum and may represent ecological or metabolic partners. We propose that Ca. Rubrimentiphilum act as efficient heterotrophic scavengers. Combined with previous studies, these data suggest that the phylum WPS-2 includes bacteria with diverse metabolic capabilities.

Network-directed efficient isolation of previously uncultivated Chloroflexi and related bacteria in hot spring microbial mats.

The perplexity of the complex multispecies community interactions is one of the many reasons why majority of the microorganisms are still uncultivated. We analyzed the entire co-occurrence networks between the OTUs of Tibet and Yunnan hot spring samples, and found that less abundant OTUs such as genus Tepidimonas (relative abundant <1%) had high-degree centricity (key nodes), while dominant OTUs particularly genus Chloroflexus (relative abundant, 13.9%) formed the peripheral vertexes. A preliminary growth-promotion assay determined that Tepidimonas sp. strain SYSU G00190W enhanced the growth of Chloroflexus sp. SYSU G00190R. Exploiting this result, an ameliorated isolation medium containing 10% spent-culture supernatant of Tepidimonas sp. strain SYSU G00190W was prepared for targeted isolation of Chloroflexi in the Tibet and Yunnan hot spring samples. 16S rRNA gene fingerprinting characterized majority of the colonies isolated from these media as previously uncultivated Chloroflexi, of which 36 are potential novel species (16S rRNA sequence identity <98.5%). Metabolomes studies indicated that the spent-culture supernatant comprises several low-molecular-weight organic substrates that can be utilized as potential nutrients for the growth of these bacteria. These findings suggested that limited knowledge on the interaction of microbes provide threshold to traditional isolation method.

Widespread microbial mercury methylation genes in the global ocean.

Methylmercury is a neurotoxin that bioaccumulates from seawater to high concentrations in marine fish, putting human and ecosystem health at risk. High methylmercury levels have been found in the oxic subsurface waters of all oceans, but only anaerobic microorganisms have been shown to efficiently produce methylmercury in anoxic environments. The microaerophilic nitrite-oxidizing bacteria Nitrospina have previously been suggested as possible mercury methylating bacteria in Antarctic sea ice. However, the microorganisms responsible for processing inorganic mercury into methylmercury in oxic seawater remain unknown. Here, we show metagenomic and metatranscriptomic evidence that the genetic potential for microbial methylmercury production is widespread in oxic seawater. We find high abundance and expression of the key mercury methylating genes hgcAB across all ocean basins, corresponding to the taxonomic relatives of known mercury methylating bacteria from Deltaproteobacteria, Firmicutes and Chloroflexi. Our results identify Nitrospina as the predominant and widespread microorganism carrying and actively expressing hgcAB. The highest hgcAB abundance and expression occurs in the oxic subsurface waters of the global ocean where the highest MeHg concentrations are typically observed.

Dictyobacter vulcani sp. nov., belonging to the class Ktedonobacteria, isolated from soil of the Mt Zao volcano.

An aerobic, Gram-stain-positive, mesophilic Ktedonobacteria strain, W12T, was isolated from soil of the Mt Zao volcano in Miyagi, Japan. Cells were filamentous, non-motile, and grew at 20-37 °C (optimally at 30 °C), at pH 5.0-7.0 (optimally at pH 6.0) and with <2 % (w/v) NaCl on 10-fold diluted Reasoner's 2A (R2A) medium. Oval-shaped spores were formed on aerial mycelia. Strain W12T hydrolysed microcrystalline cellulose and xylan very weakly, and used d-glucose as its sole carbon source. The major menaquinone was MK-9, and the major cellular fatty acids were C16 : 1 2-OH, iso-C17 : 0, summed feature 9 (10-methyl C16 : 0 and/or iso-C17 : 1ω9c) and anteiso-C17 : 0. Cell-wall sugars were mannose and xylose, and cell-wall amino acids were d-glutamic acid, glycine, l-serine, d-alanine, l-alanine, ß-alanine and l-ornithine. Polar lipids were phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, an unidentified glycolipid and an unidentified phospholipid. Strain W12T has a genome of 7.42 Mb with 49.7 mol% G+C content. Nine copies of 16S rRNA genes with a maximum dissimilarity of 1.02 % and 13 biosynthetic gene clusters mainly coding for peptide products were predicted in the genome. Phylogenetic analysis based on both 16S rRNA gene and whole genome sequences indicated that strain W12T represents a novel species in the genus Dictyobacter. The most closely related Dictyobacter type strain was Dictyobacter alpinus Uno16T, with 16S rRNA gene sequence similarity and genomic average nucleotide identity of 98.37 % and 80.00 %, respectively. Herein, we propose the name Dictyobacter vulcani sp. nov. for the type strain W12T (=NBRC 113551T=BCRC 81169T) in the bacterial class Ktedonobacteria.

Temporal and spatial variations in the bacterial community composition in Lake Bosten, a large, brackish lake in China.

The bacteria inhabiting brackish lake environments in arid or semi-arid regions have not been thoroughly identified. In this study, the 454 pyrosequencing method was used to study the sedimentary bacterial community composition (BCC) and diversity in Lake Bosten, which is located in the arid regions of northwestern China. A total of 210,233 high-quality sequence reads and 8,427 operational taxonomic units (OTUs) were successfully obtained from 20 selected sediment samples. The samples were quantitatively dominated by members of Proteobacteria (34.1% ± 11.0%), Firmicutes (21.8% ± 21.9%) and Chloroflexi (13.8% ± 5.2%), which accounted for more than 69% of the bacterial sequences. The results showed that (i) Lake Bosten had significant spatial heterogeneity, and TOC(total organic carbon), TN(total nitrogen) and TP(total phosphorus) were the most important contributors to bacterial diversity; (ii) there was lower taxonomic richness in Lake Bosten, which is located in an arid region, than in reference lakes in eutrophic floodplains and marine systems; and (iii) there was a low percentage of dominant species in the BCC and a high percentage of unidentified bacteria. Our data help to better describe the diversity and distribution of bacterial communities in contaminated brackish lakes in arid regions and how microbes respond to environmental changes in these stable inland waters in arid or semi-arid regions.

Extremophilic nitrite-oxidizing Chloroflexi from Yellowstone hot springs.

Nitrifying microorganisms occur across a wide temperature range from 4 to 84 °C and previous studies in geothermal systems revealed their activity under extreme conditions. Archaea were detected to be responsible for the first step of nitrification, but it is still a challenging issue to clarify the identity of heat-tolerant nitrite oxidizers. In a long-term cultivation approach, we inoculated mineral media containing ammonium and nitrite as substrates with biofilms and sediments of two hot springs in Yellowstone National Park (USA). The nitrifying consortia obtained at 70 °C consisted mostly of novel Chloroflexi as revealed by metagenomic sequencing. Among these, two deep-branching novel Chloroflexi were identified as putative nitrite-oxidizing bacteria (NOB) by the presence of nitrite oxidoreductase encoding genes in their genomes. Stoichiometric oxidation of nitrite to nitrate occurred under lithoautotrophic conditions, but was stimulated by organic matter. Both NOB candidates survived long periods of starvation and the more abundant one formed miniaturized cells and was heat resistant. This detection of novel thermophilic NOB exemplifies our still incomplete knowledge of nitrification, and indicates that nitrite oxidation might be an ancient and wide-spread form of energy conservation.

Ktedonosporobacter rubrisoli gen. nov., sp. nov., a novel representative of the class Ktedonobacteria, isolated from red soil, and proposal of Ktedonosporobacteraceae fam. nov.

A novel filamentous, spore-forming, Gram-stain-positive bacterium, designated SCAWS-G2T, was isolated from red soil in Jiangxi Province, PR China. The strain grew at 25-45 °C and at pH 4.0-7.0, and was able to tolerate up to 50 mM Zn2+. The complete genome of strain SCAWS-G2T was a circular chromosome of ~11.34 Mb, which contained four 16S rRNA genes with three sequence types (0.4-0.8 % differences). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain SCAWS-G2T formed a distinct lineage within the order Ktedonobacterales, showing <89.2 % sequence similarities to the recognized taxa of this order. The whole-genome based phylogenomic tree separated strain SCAWS-G2T from the recognized families within Ktedonobacterales. The genome-wide average nucleotide identity values between strain SCAWS-G2T and the related type strains were <68.2 %. The strain can also be differentiated from the recognized families by a number of phenotypic characteristics. The polar lipids of SCAWS-G2T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, seven unidentified glycolipids and one unidentified lipid. The peptidoglycan amino acids contained ornithine, glycine, glutamic acid and alanine, and the cell-wall sugars were mainly galactose and rhamnose. The major fatty acids were C16 : 1 2-OH, C16 : 0 and iso-C17 : 0. Based on all these data, we propose that strain SCAWS-G2T represents a novel genus and species, Ktedonosporobacter rubrisoli gen. nov., sp. nov., within the new family Ktedonosporobacteraceae fam. nov. of the order Ktedonobacterales. The type strain of Ktedonosporobacter rubrisoli is SCAWS-G2T (=CGMCC 1.16132T=DSM 105258T).

Microbial communities of the Laurentian Great Lakes reflect connectivity and local biogeochemistry.

The Laurentian Great Lakes are a vast, interconnected freshwater system spanning strong physicochemical gradients, thus constituting a powerful natural laboratory for addressing fundamental questions about microbial ecology and evolution. We present a comparative analysis of pelagic microbial communities across all five Laurentian Great Lakes, focusing on Bacterial and Archaeal picoplankton characterized via 16S rRNA amplicon sequencing. We collected samples throughout the water column from the major basins of each lake in spring and summer over 2 years. Two oligotypes, classified as LD12 (Alphaproteobacteria) and acI-B1 (Actinobacteria), were among the most abundant in every sample. At the same time, microbial communities showed distinct patterns with depth during summer stratification. Deep hypolimnion samples were frequently dominated by a Chloroflexi oligotype that reached up to 19% relative abundance. Stratified surface communities differed between the colder, less productive upper lakes (Superior, Michigan, Huron) and warmer, more productive lower lakes (Erie, Ontario), in part due to an Actinobacteria oligotype (acI-C2) that averaged 7.7% of sequences in the lower lakes but <0.2% in the upper lakes. Together, our findings suggest that both hydrologic connectivity and local selective pressures shape microbial communities in the Great Lakes and establish a framework for future investigations.

Water-soluble phosphorus contributes significantly to shaping the community structure of rhizospheric bacteria in rocky desertification areas.

Microorganisms play important roles in soil improvement. Therefore, clarifying the contribution of environmental factors in shaping the microbial community structure is beneficial to improve soil fertility in karst rocky desertification areas. Here, the bacterial community structures of eight rhizospheric soil samples collected from perennial fruit plantations were analysed using an Illumina HiSeq2500 platform. The diversity and abundance of bacteria in rocky desertification areas were significantly lower than those in non-rocky desertification areas, while the bacterial community structure was not significantly different between root surface and non-root surface soils in the same rhizospheric soil samples. Proteobacteria predominated in rocky desertification areas, while Actinobacteria predominated in non-rocky desertification areas. Correlation analysis revealed that water-soluble phosphorus content (r2 = 0.8258), latitude (r2 = 0.7556), altitude (r2 = 0.7501), and the age of fruit trees (r2 = 0.7321) were positively correlated with the bacterial community structure, while longitude, pH, and total phosphorus content did not significantly influence the soil bacterial community structure. As water-soluble phosphorus content is derived from insoluble phosphorus minerals, supplementing phosphorus-solubilising bacteria to soils in rocky desertification areas is a feasible strategy for accelerating the dissolution of insoluble phosphorus minerals and improving agricultural production and environment ecology.

Antibiotic resistance and microbiota in the gut of Chinese four major freshwater carp from retail markets.

Fish-associated antibiotic resistance genes (ARGs) have attracted increasing attention due to their potential risks to human beings via the food chain. However, data are scarce regarding the antibiotic resistance in fish themselves. Herein, the antibiotic resistance genes (ARGs) were assessed in the gut of four major Chinese freshwater carp (i.e., silver carp, grass carp, bighead carp, and crucian carp) from food retail markets. Results show that the abundances of target ARGs (e.g., tetA, tetO, tetQ, tetW, sulI, sulII, and blaTEM-1) and class 1 integrase (intI1) were in the range 9.4 × 10-6 - 1.6 × 10-1 and 6.7 × 10-5 - 5.2 × 10-2 gene copies per 16S rRNA gene, respectively. The sulI, sulII, and tetQ strongly correlated with silver and mercury resistance genes (e.g., silE and merR). The microbial taxa of fish gut could be partly separated among retail markets based on the PCA analysis. About 15.0% of the OTUs in fish gut were shared and 74.5% of the shared OTUs were identified as Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, and Proteobacteria. These phyla may constitute the core microbiota in the guts of the four Chinese freshwater carp. The possible ARG hosts were revealed based on the network analysis, and the presence of pathogen-associated resistant genera in fish gut highlights the need to fully understand their potential human health risks.

Diversity of tryptophan halogenases in sponges of the genus Aplysina.

Marine sponges are a prolific source of novel enzymes with promising biotechnological potential. Especially halogenases, which are key enzymes in the biosynthesis of brominated and chlorinated secondary metabolites, possess interesting properties towards the production of pharmaceuticals that are often halogenated. In this study we used a polymerase chain reaction (PCR)-based screening to simultaneously examine and compare the richness and diversity of putative tryptophan halogenase protein sequences and bacterial community structures of six Aplysina species from the Mediterranean and Caribbean seas. At the phylum level, bacterial community composition was similar amongst all investigated species and predominated by Actinobacteria, Chloroflexi, Cyanobacteria, Gemmatimonadetes, and Proteobacteria. We detected four phylogenetically diverse clades of putative tryptophan halogenase protein sequences, which were only distantly related to previously reported halogenases. The Mediterranean species Aplysina aerophoba harbored unique halogenase sequences, of which the most predominant was related to a sponge-associated Psychrobacter-derived sequence. In contrast, the Caribbean species shared numerous novel halogenase sequence variants and exhibited a highly similar bacterial community composition at the operational taxonomic unit (OTU) level. Correlations of relative abundances of halogenases with those of bacterial taxa suggest that prominent sponge symbiotic bacteria, including Chloroflexi and Actinobacteria, are putative producers of the detected enzymes and may thus contribute to the chemical defense of their host.

'Candidatus Oscillochloris fontis': a novel mesophilic phototrophic Chloroflexota bacterium belonging to the ubiquitous Oscillochloris genus.

We present the results of a study of mesophilic anoxygenic phototrophic Chloroflexota bacteria from Mechigmen hot spring (the Chukotka Peninsula) and Siberia. According to 16S rRNA phylogenetic analysis, these bacteria belong to Oscillochloris trichoides. However, sequencing the draft genome of the bacterium from the Chukotka and analysis of the average nucleotide identity, as well as in silico DNA-DNA hybridization, reveal that this bacterium belongs to a novel species within the Oscillochloris genus. We, therefore, propose 'Candidatus Oscillochloris fontis' as a novel taxon to represent this mesophilic alkaliphilic anaerobic anoxygenic phototrophic bacterium. Spectrophotometry and high-performance liquid chromatography analysis show that the bacterium possesses bacteriochlorophylls c and a, as well as lycopene, ß-carotene and γ-carotene. In addition, transmission electron microscopy shows the presence of chlorosomes, polyhydroxyalkanoate- and polyphosphate-like granules. The genome of 'Ca. Oscillochloris fontis' and the Siberian strains of Oscillochloris sp. possess the key genes for nitrogenase complex (nifH) and ribulose-1,5-bisphosphate carboxylase/oxygenase (cbbL), as previously described for O. trichoides DG-6. The results presented here, and previously published data, show that Oscillochloris bacteria from different aquatic environments have the potential for CO2 and N2 fixation. Additionally, we describe a new primer system for the detection of RuBisCo form I.

Thermogemmatispora aurantia sp. nov. and Thermogemmatispora argillosa sp. nov., within the class Ktedonobacteria, and emended description of the genus Thermogemmatispora.

Two thermophilic, aerobic, Gram-stain-positive Ktedonobacteria strains, A1-2T and A3-2T, were isolated from geothermal soil in Japan. The strains formed orange-coloured colonies on 10-fold diluted Reasoner's 2A medium, followed by formation of branched aerial mycelium with multiple grape-like spores. Both strains hydrolysed casein, carboxymethyl cellulose, starch, chitin and xylan, but did not liquify gelatin. Strain A1-2T utilised sucrose and gellan gum and was inhibited by inositol, while strain A3-2T utilised only gellan gum and was not inhibited by inositol. The DNA G+C contents of strain A1-2T and A3-2T were 63.2 and 63.1 mol%, respectively. Chemotaxonomic data (major fatty acid, iso-C17 : 0; major menaquinone, MK-9(H2); cell-wall amino acids, ornithine, serine, glycine, glutamic acid, alanine and ß-alanine; polar lipids, phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, one unidentified lipid, one unidentified phosphoglycolipid and three unidentified glycolipids; major cell-wall sugars, mannose, arabinose and xylose) indicate that both strains belong to the genus Thermogemmatispora. 16S rRNA gene sequence analysis indicated that strain A1-2 T was most closely related to the type strains of Thermogemmatispora onikobensis (97.7 % sequence similarity), and that strain A3-2T was most closely related to the type strains of Thermogemmatispora carboxidivorans(97.2%), but DNA-DNA hybridization shows relatedness values of <67 % with previously described type strains. Moreover, 16S rRNA gene sequence similarity and DNA-DNA relatedness between strain A1-2T and strain A3-2T were 96.0 and 33.4%, respectively, suggesting that the two strains are genetically distinct. The two strains are proposed as Thermogemmatispora aurantia sp. nov. and Thermogemmatispora argillosa sp. nov.