New Proteins Involved in Sulfur Trafficking in the Cytoplasm of Allochromatium vinosum [Metabolism]

March 19th, 2014 by Stockdreher, Y., Sturm, M., Josten, M., Sahl, H.-G., Dobler, N., Zigann, R., Dahl, C.

The formation of periplasmic sulfur globules is an intermediate step during the oxidation of reduced sulfur compounds in various sulfur- oxidizing microorganisms. The mechanism of how this sulfur is activated and crosses the cytoplasmic membrane for further oxidation to sulfite by the dissimilatory reductase DsrAB is incompletely understood, but it has been well documented that the pathway involves sulfur trafficking mediated by sulfur caryying proteins. So far, sulfur transfer from DsrEFH to DsrC has been established. Persulfurated DsrC very probably serves as a direct substrate for DsrAB. Here, we introduce further important players in oxidative sulfur metabolism: The proteins Rhd_2599, TusA and DsrE2 are strictly conserved in the Chromatiaceae, Chlorobiaceae and Acidithiobacillaceae families of sulfur oxidizing bacteria and are linked to genes encoding complexes involved in sulfur oxidation (Dsr or Hdr) in the latter two. Here, we show via relative qRT-PCR and microarray analysis an increase of mRNA levels under sulfur-oxidizing conditions for rhd_2599, tusA and dsrE2 in Allochromatium vinosum. Transcriptomic patterns for the three genes match those of major genes for the sulfur-oxidizing machinery rather than those involved in biosynthesis of sulfur-containing biomolecules. TusA appears to be one of the major proteins in Alc. vinosum. A rhd_2599-tusA-dsrE2 deficient mutant strain - though not viable in liquid culture - was clearly sulfur oxidation negative upon growth on solid media containing sulfide. Rhd_2599, TusA and DsrE2 bind sulfur atoms via conserved cysteine residues and experimental evidence is provided for the transfer of sulfur between these proteins as well as to DsrEFH and DsrC.