# Identification of Volatile Sulfur Compounds Produced by _Schizophyllum commune_
## 4 Discussion  
Through this study, we determined VSCs including DMDS, DMTriS, DMTetraS, MEDS, DEDS, and H\({}_{2}\)S as the major VOCs of _S. commune_. Polysulfides are well-known odor VSCs [15; 16]. Additionally, DMDS and DMTriS are distributed widely in cooked vegetables, beverages, and foods [17; 18; 19; 20]. VSCs are produced by various microbes including bacteria (_Brevibacterium lines_) and yeasts (e.g., _Geotrich candidium_, _Yarrowia lipolytica_, and _Candidia_ spp.) [21; 22; 23; 24]. Among molds, truffles (_Tuber_ spp.) are well-known producers of VSCs including DMDS and DMTriS [25]. Those VSCs are thought to be derived mainly from L-methionine or \(\alpha\)-keto-\(\gamma\)-methylthiobutyric acid via methanethiol production [25]. Cystathionine \(\gamma\)-lyase and cystathionine \(\gamma\)-lyase produce methanethiol from L-methionine with lower efficiency. Cystathionine lyase homologs are found in _S. commune_[26]. Cystathionine \(\gamma\)-lyase was a highly expressed gene in fruiting bodies of _Tuber melanosporum_. Cystathionine \(\gamma\)-lyase is upregulated in fruiting bodies of _T. melanosporum_ compared to free-living mycelia [27]. The reason why _S. commune_ mycelia actively produced these VSCs remains unknown. Further research is expected to reveal the importance of these genes and the precise roles of VSCs. As shown in Figure 2, dimethyl polysulfide production showed high correlation coefficients, suggesting that the methyl group is derived from methanethiol as described above. However, the correlation coefficients between DEDS and dimethyl polysulfides are very low (\(R^{2}\) is less than 0.02, not significant). The ethyl group in DEDS and MEDS might be derived from ethanethiol [28; 29] because ethanol is a major VOC of _S. commune_[13] and because H\({}_{2}\)S can react with ethanol to give ethanethiol in vitro [28]. The difference between the methyl group and ethyl group supplies might be attributable to the low correlation coefficients of the ion peak area between DEDS and dimethyl polysulfides. VSCs are found widely in nature as described above. Particularly, DMTetraS were found specifically as salivaal VSCs in patients with halitosis, but not in healthy individuals [30]. Additionally, DMTriS was detected frequently from samples of patients with halitosis, although it was also detected in healthy individuals [30]. [PERSON] et al. reported DMTriS as a characteristic odor detected from fungating cancer wounds, although other sources such as associated bacteria contributed to the production [31]. In reports of both studies, the authors describe that polysulfides are candidates of biomarkers to diagnose specific diseases. The VSCs determined in _S. commune_ culture might be candidates of biomarkers for the diagnosis of ABPM by _S. commune_ from sputum, breath, and culture plates. Furthermore, we observed that VOCs turned lead acetate paper black during _S. commune_ culture. Lead acetate paper is commonly used to detect H\({}_{2}\)S sulfur odorants. Results show that _S. commune_ produces H\({}_{2}\)S rapidly. Although the color of lead acetate paper was slightly changed (but comparable to control blanks) by the head space air of \(A\). Figure 5: Detection of H\({}_{2}\)S using lead acetate paper. The whiteness of lead acetate. fumigatus_ under a four-day culture, the application also might be useful to determine _S. commune_ as a causative agent of ABPM. Currently, we are trying to conduct research using clinical specimens. [PERSON] et al. demonstrated that volatile dimethyl sulfide and DMDS support _A. fumigatus_ growth [32]. _Pseudomonas aeruginosa_, which is the major bacterial pathogen causing lung infections, is a producer of VSCs [32, 33]. Similar to _P. aeruginosa_, VSCs from _S. commune_ might support _A. fumigatus_ growth in shared headspace. Both _S. commune_ and _A. fumigatus_ are causative agents of ABPM and fungal rhinusitis. Several coinfection cases have been reported [34, 35, 36]. Although the cases are rare, interspecies interaction might occur in the infection focus.