Purple non-sulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria harnessing simple organic acids as electron donors. PNSB produce a-aminolevulinic acid, polyhydroxyalcanoates, bacteriochlorophylls a and b, ubiquinones, and other valuable compounds. They are highly promising producers of molecular hydrogen. PNSB can be cultivated in organic waste waters, such as wastes after fermentation. In most cases, wastes mainly contain acetic acid. Therefore, understanding the anaplerotic pathways in PNSB is crucial for their potential application as producers of biofuels. The present review addresses the recent data on presence and diversity of anaplerotic pathways in PNSB and describes different classifications of these pathways.

The purple sulfur bacterium Thiocapsa roseopersicina BBS is interesting from both fundamental and practical points of view. It possesses a thermostable HydSL hydrogenase, which is involved in the reaction of reversible hydrogen activation and a unique reaction of sulfur reduction to hydrogen sulfide. It is a very promising enzyme for enzymatic hydrogenase electrodes. There are speculations that HydSL hydrogenase of purple bacteria is closely related to sulfur metabolism, but confirmation is required. For that, the full genome sequence is necessary. Here, we sequenced and assembled the complete genome of this bacterium. The analysis of the obtained whole genome, through an integrative approach that comprised estimating the Average Nucleotide Identity (ANI) and digital DNA-DNA hybridization (DDH) parameters, allowed for validation of the systematic position of T. roseopersicina as T. bogorovii BBS. For the first time, we have assembled the whole genome of this typical strain of a new bacterial species and carried out its functional description against another purple sulfur bacterium: Allochromatium vinosum DSM 180T. We refined the automatic annotation of the whole genome of the bacteria T. bogorovii BBS and localized the genomic positions of several studied genes, including those involved in sulfur metabolism and genes encoding the enzymes required for the TCA and glyoxylate cycles and other central metabolic pathways. Eleven additional genes coding proteins involved in pigment biosynthesis was found.

The specific enzymatic reaction of sulfur reduction to hydrogen sulfide catalyzed by the HydSL hydrogenase of T. bogorovii BBS has so far been observed only in native cells. In this work, we were able to detect the hydrogen-dependent reaction H₂ + S⁰ → H₂S + HS^– + H⁺ in a cell homogenate of these bacteria. This was achieved by destroying the cells in an optimized buffer of high ionic strength. Further purification of the preparation led to a 28-fold increase in its specific activity.

The culturing conditions for the production of cells of the purple nonsulfur bacteria Rba. capsulatus, which possess a minimal capsule, are selected and the effectiveness of their use in induced transformation by electroporation to transfer exogenous DNA in comparison with cells cultivated on other types of conventionally used media is shown. It is found that, upon the electroporation of plasmid DNA (pDNA) into the cells of Rba. capsulatus according to the selected procedure, the survival rate of the culture is an unstable quantity, which requires optimization of the conditions for obtaining electrocompetent cells and careful selection of the electric-shock treatment mode. For the first time, the fundamental possibility of using an approach for protection against the destruction of pDNA by the restriction modification system (RMS) of Rba. capsulatus by means of in vitro methylation with a cell-free extract of this culture, as well as transformation of the treated pDNA into competent cells of this bacterium by electroporation is demonstrated.