Genome-guided insights into the versatile metabolic capabilities of the mercaptosuccinate-utilizing β-proteobacterium Variovorax paradoxus strain B4.

Variovorax paradoxus B4 is able to utilize 2-mercaptosuccinate (MS) as sole carbon, sulfur and energy source. The whole genome of V. paradoxus B4 was sequenced, annotated and evaluated with special focus on genomic elements related to MS metabolism. The genome encodes two chromosomes harbouring 5 795 261 and 1 353 255 bp. A total of 6753 putative protein-coding sequences were identified. Based on the genome and in combination with results from previous studies, a putative pathway for the degradation of MS could be postulated. The putative molybdopterin oxidoreductase identified during transposon mutagenesis probably catalyses the conversion of MS first into sulfinosuccinate and then into sulfosuccinate by successive transfer of oxygen atoms. Subsequently, the cleavage of sulfosuccinate yields oxaloacetate and sulfite, while the latter is oxidized to sulfate. The expression of the putative molybdopterin oxidoreductase was induced by MS, but not by gluconate, as confirmed by reverse transcriptase polymerase chain reaction. Further, in silico studies combined with experiments and comparative genomics revealed high metabolic diversity of strain B4. It bears a high potential as plant growth-promoting bacterium and as candidate for degradation and detoxification of xenobiotics and other hardly degradable substances. Additionally, the strain is of special interest for production of polythioesters with sulfur-containing precursors as MS.