However, a significant induction (4-5 fold) was found for a tricistronic operon, Dhaf_0248-0250, which encodes a putative cytochrome b-containing nitrate

reductase gamma subunit, a cysteine-rich ferredoxin protein, and a NADH oxydase-like protein. This operon, together with the type IV pilus biosynthesis operon (~10 fold induction), may play roles in the formation and transport of electrons for U(VI) reduction. Although toxic at higher concentrations (MIC of ~0.1 mM for Escherichia coli [41]), selenite is required by microbes as the source for selenocysteine and selenomethionine [42]. Selenocysteine supplies selenium to glycine reductase, formate dehydrogenase, and NiFeSe hydrogenase [43, 44]. D. hafniense DCB-2 reduces selenate [Se(VI)] to selenite [Se(IV)] and then to elemental selenium Copanlisib mouse [Se(0)] [6, 25]. It is not clear, however, whether selenate reduction is coupled to energy generation in this organism. A homolog for the well-characterized selenate reductase (SER) from Thauera selenatis [45, 46] was not identified in the DCB-2 genome. However, a putative dmsABC operon (Dhaf_1954-1956) that belongs to the same DMSO reductase family of type II molybdoenzymes was significantly induced under selenate-reducing conditions. Interestingly, a putative

selleck chemical sulfite reductase α subunit encoded by Dhaf_0252, when produced in E. coli BL21-A1 via the expression vector pDEST17, mediated the reduction of selenate but not selenite (data not shown). This gene is part of an eleven-gene dissimilatory sulfite reductase operon (Dsr operon, Dhaf_0251-0261), the products of which catalyze the six-electron reduction of sulfite to sulfide. While sulfite reductase of Clostridium pasteurianum and nitrite reductase of Thauera clonidine selenatis have been implicated in selenite reduction [47, 48], selenate reduction by sulfite reductase has not been reported. Arsenic is readily metabolized by microbes through oxidation/reduction reactions

in resistance and respiration processes [49–51]. D. hafniense DCB-2 is capable of reducing arsenate [As(V)] to arsenite [As(III)] for respiration [6, 25], and the genes for the respiratory arsenate reductase (arrABC, Dhaf_1226-1228) are present in its genome. The catalytic subunit, ArrA, contains a molybdenum binding motif that shares a significant homology in amino acid sequence with those of other bacterial respiratory arsenate reductases [51]. Detoxification of arsenic in DCB-2 may be a consequence of arsenic reduction coupled to the arsenite efflux apparatus [49, 50]. Three arsenate reductase genes, arsC, were identified at different locations (Dhaf_1210, 2269, 2937), and a component for the potential arsenite efflux pump was found as a closely-linked gene (Dhaf_1212).