A novel pathway for the catabolism of the organic sulfur compound 3,3'-dithiodipropionic acid via 3-mercaptopropionic acid and 3-sulfinopropionic acid to propionyl-CoA by the aerobic bacterium Tetrathiobacter mimigardefordensis strain DPN7

Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

^* To whom correspondence should be addressed. Email: steinbu{at}uni-muenster.de.

	Abstract

The hitherto not studied microbial degradation of the organic disulfide 3,3'-dithiodipropionic acid (DTDP) was investigated in the recently described bacterium Tetrathiobacter mimigardefordensis strain DPN7^T (DSM 17166^T; LMG 22922^T) which is able to use DTDP as sole carbon source for growth. 3-Mercaptopropionic acid (3MP) and 3-sulfinopropionic acid (3SP) were detected in the growth medium and occurred as intermediates during DTDP degradation. To identify genes coding for enzymes of DTDP catabolism, Tn5::mob-induced mutants of T. mimigardefordensis were generated. Screening of transposon mutant libraries yielded many mutants fully or partially impaired in utilizing DTDP as carbon source. Mapping of the insertion loci in some mutants identified four disrupted open reading frames (ORFs) with putative metabolic functions. The ORFs were assigned function on the basis of homologies as lpdA (EC 1.8.1.4), cdo (EC 1.13.11.20), sucCD (EC 6.2.1.5) or acnB (EC 4.1.2.3), respectively. Tn5::mob insertions occurred additionally also in the vicinity of heat shock protein encoding genes. The predicted function of the LpdA homologue in T. mimigardefordensis is cleavage of the disulfide bound of DTDP into two molecules of 3MP. Cdo catalyzes the conversion of the sulfhydryl group of 3MP yielding the corresponding sulfinic acid, 3SP. SucCD exhibits thiokinase activity, ligating coenzyme A with 3SP to 3SP-CoA. Afterwards, an elimination of sulfite via a putative desulfinase is expected. AcnB encodes a putative 2-methylisocitrate dehydratase. Therefore, a new pathway is proposed for the catabolism of DTDP via 3MP, 3SP and 3SP-CoA towards propionyl-CoA which is then further catabolized via the 2-methylcitric acid cycle in T. mimigardefordensis.