Transcriptomic and proteomic insight into the mechanism of cyclooctasulfur- versus thiosulfate-oxidation by the chemolithoautotroph Sulfurimonas denitrificans

Chemoautotrophic bacteria belonging to the genus Sulfurimonas (class Campylobacteria) were previously identified as key players in the turnover of zero-valence sulfur, a central intermediate in the marine sulfur cycle. S. denitrificans was further shown to be able to oxidize cyclooctasulfur (S-8). However, at present the mechanism of activation and metabolism of cyclooctasulfur is not known. Here, we assessed the transcriptome and proteome of S. denitrificans grown with either thiosulfate or S-8 as the electron donor. While the overall expression profiles under the two growth conditions were rather similar, distinct differences were observed that could be attributed to the utilization of S-8. This included a higher abundance of expressed genes related to surface attachment in the presence of S-8, and the differential regulation of the sulfur-oxidation multienzyme complex (SOX), which in S. denitrificans is encoded in two gene clusters: soxABXY(1)Z(1) and soxCDY(2)Z(2). While the proteins of both clusters were present with thiosulfate, only proteins of the soxCDY(2)Z(2) were detected at significant levels with S-8. Based on these findings a model for the oxidation of S-8 is proposed. Our results have implications for interpreting metatranscriptomic and -proteomic data and for the observed high level of diversification of soxY(2)Z(2) among sulfur-oxidizing Campylobacteria.