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 (S8 ). 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 S8 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 S8 . This included a higher abundance of expressed genes related to surface attachment in the presence of S8 , 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 S8 . Based on these findings a model for the oxidation of S8 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.