Search

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, β-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., (© FEMS 2019.)

In this article, we present the description of a novel mesophilic phototrophic Chloroflexi bacterium, 'Candidatus Viridilinea mediisalina' Kir15-3F. We have isolated an anaerobic, highly enriched culture of this bacterium from the Kiran soda lake (Siberia) and optimized its cultivation. Metagenomic sequencing revealed that 'Ca. Viridilinea mediisalina' Kir15-3F is a bacteriochlorophyll-containing Chloroflexi bacterium in the enrichment culture. Fluorescent in situ hybridisation demonstrated a link between the phenotype described here and the 'Ca. Viridilinea mediisalina' Kir15-3F genome. Spectrophotometry and high-performance liquid chromatography analyses showed the presence of bacteriochlorophylls d, c and a, as well as lycopene, γ-carotene and β-carotene. Transmission electron microscopy showed chlorosomes, gas vesicles, polyhydroxyalkanoate-like and polyphosphate-like granules. Our results illustrated that 'Ca. Viridilinea mediisalina' Kir15-3F is an alkaliphilic, salt-tolerant, obligately mesophilic, anaerobic, phototrophic bacterium. The genome sequences lack genes of the Calvin cycle and a sulphide:quinone reductase gene for sulphide oxidation. Owing to the lack of an axenic culture and based on the genomic and phenotypic data, we have presented the description of the bacterium in the Candidatus category., (© FEMS 2019.)