Physiological studies of wood rotting fungi have mostly focused on the metabolism of carbon and nitrogen sources, which constitute the dominants components of wood. On the other hand, despite the physiological importance of trace elements such as sulfur, studies on their acquisition sources and metabolic pathways are limited. Until now, wood rotting fungi have been thought to utilize slight amounts of water-soluble sulfur compounds, such as sulfate-ester and thiol, in wood as a source of sulfur. Recently, we found that a soil filamentous fungus Trichoderma harzianum not only can degrade carbonyl sulfide (COS), which is the most abundant gaseous sulfur molecule in the atmosphere, but also use it as a source of sulfur. In addition to T. harzianum, we have found that several wood rotting fungi were able to degrade COS. We investigated the COS degradation and its metabolism in Gloeophyllum trabeum NBRC 6430, a model brown-rot fungus, and found that COS affects its growth and sulfur metabolites. Based on the results, we hypothesized that wood rotting fungi can use COS as one of sulfur sources when they colonize the wood in which sulfur content has been known to be quite low. In the present study, to gain further knowledge of COS metabolism and its mechanism by wood rotting fungi, we investigated gene expression patterns in G. trabeum NBRC 6430 exposed COS. As a result, the expression level of the several genes tended to change depending on the amount of COS exposed. Among them, we found a candidate gene that is directly related to COS degradation, and then the recombinant enzyme heterologously produced by E. coli was analyzed from the viewpoint of enzymatic characteristics. As a result, we found that the candidate gene encodes COS hydrolytic enzyme (called COS hydrolase or COSase, COS + H2O → CO2 + H2S). The results provide a new insight into the nutritional acquisition pathway in wood rotting fungi.

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