'Candidatus Chloroploca mongolica' sp. nov. a new mesophilic filamentous anoxygenic phototrophic bacterium.

A mesophilic filamentous anoxygenic phototrophic bacterium, designated M50-1, was isolated from a microbial mat of the Chukhyn Nur soda lake (northeastern Mongolia) with salinity of 5-14 g/L and pH 8.0-9.3. The organism is a strictly anaerobic phototrophic bacterium, which required sulfide for phototrophic growth. The cells formed short undulate trichomes surrounded by a thin sheath and containing gas vesicles. Motility of the trichomes was not observed. The cells contained chlorosomes. The antenna pigments were bacteriochlorophyll d and ß- and γ-carotenes. Analysis of the genome assembled from the metagenome of the enrichment culture revealed all the enzymes of the 3-hydroxypropionate bi-cycle for autotrophic CO2 assimilation. The genome also contained the genes encoding a type IV sulfide:quinone oxidoreductase (sqrX). The organism had no nifHDBK genes, encoding the proteins of the nitrogenase complex responsible for dinitrogen fixation. The DNA G + C content was 58.6%. The values for in silico DNA‒DNA hybridization and average nucleotide identity between M50-1 and a closely related bacterium 'Ca. Chloroploca asiatica' B7-9 containing bacteriochlorophyll c were 53.4% and 94.0%, respectively, which corresponds to interspecies differences. Classification of the filamentous anoxygenic phototrophic bacterium M50-1 as a new 'Ca. Chloroploca' species was proposed, with the species name 'Candidatus Chloroploca mongolica' sp. nov.

'Candidatus Viridilinea mediisalina', a novel phototrophic Chloroflexi bacterium from a Siberian soda lake.

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 ß-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.