Figure 5 shows a schematic overview of the different genes that are involved in the oxidation of sulfur compounds. The genome of Thioalkalivibrio sp. K90mix contains genes for flavocytochrome c/sulfide dehydrogenase www.selleckchem.com/products/AG-014699.html (TK90_0236), which oxidizes sulfide to elemental sulfur. It contains an incomplete set of sox genes including soxYZ (TK90_0123 and TK90_0124), soxAX (TK90_0432 and TK90_0433) and two copies of soxB (TK90_0627 and TK90_1150), but is lacking soxCD, which would allow oxidizing the sulfane atom of thiosulfate to the state of elemental sulfur, but no further. However, it does not contain the reverse dissimilatory sulfite reduction pathway to oxidize sulfur to sulfite, which has been found in the genome of ��Thioalkalivibrio sulfidophilus�� HLEbGr7 [32].

Absence of dsr genes has also been found for the green sulfur bacterium Chloroherpeton thalassium that can oxidize sulfide to elemental sulfur, but subsequently can only oxidize the produced sulfur very slowly [34], probably due to the absence of dsr. Frigaard and Dahl [35] suggested that the presence of a RuBisCo-like protein (RLP) might be involved in sulfur oxidation [36]. Genes encoding for the RuBisCo-like protein were not found, nor were genes encoding sulfur dioxygenase or sulfur oxygenase-reductase, which can oxidize or disproportionate sulfur in several acidophilic bacteria and archaea [37]. However, we found a gene cluster encoding two sulfur transferases (rhd, TK90_0630; sirA, TK90_0631) and a heterodisulfide reductase complex (TK90_0632 – TK90_0637) consisting of hdrA, hdrB, and hdrC (Figure 6).

dsrE was missing in this cascade, but was present at 3 other places in the genome (TK_0511, TK_0639, TK90_1244). Figure 5 Schematic overview of the different genes that are involved in the oxidation of sulfur compounds, although the role of the Hdr complex has not been proven yet. The genes encoding the reverse dissimilatory sulfite reductase (dsr), which are present in … Figure 6 Comparison of the hdr cluster of A. ferroooxidans ATCC 23270 (AF), Thioalkalivibrio sp. K90mix (K90) and Thioalkalivibrio sulfidophilus HL-EbGR7 (HL). The heterodisulfide reductase complex consists of the genes encoding HdrC1, HdrB1, HdrA, orf2, HdrC2 … The Hdr complex plays a function in the energy metabolism of methanogens [38] and sulfate-reducing prokaryotes [39].

In methanogens, the enzyme complex catalyzes the reversible reduction of the disulfide (CoM-S-S-CoB) of the two methanogenic thiol-coenzymes, coenzyme M (CoM-SH) and coenzyme B (CoB-SH); in sulfate reducing microorganisms the substrate (X-S-S-X) is not known. Recently, the genes encoding the Hdr complex have also been detected in the genomes of the acidophilic sulfur oxidizing bacteria Acidithiobacillus ferrooxidans [40] and Acidithiobacillus caldus [41]. Quantrini and co-workers [40] hypothesized that Hdr, like the dissimilatory sulfite reductase (dsr), is working Brefeldin_A in reverse, whereby sulfur (i.e.