## 3 Discussion
Curiously, some compounds frequently reported in other studies on microbial VOCs were also identified in this study, but only in the controls of culture media without yeast; for instance, broadly studied 1-octen-3-ol, which has been reported as a characteristic volatile of fungi [11; 17; 30; 46; 47; 48], and the compounds dimethyl sulfide and dimethyl disulfide, which have been shown to be related to biological and microbial interactions [22; 49; 50], were identified in our control media. Some of these compounds were reported in a study on VOCs for _M. furfur_[12]. It is strange that compounds widely studied in bacteria and fungi, such as those mentioned above, were found in our controls, so an exhaustive review was conducted to reject any contamination in the control media or mistakes in the data analysis. We concluded that there was no contamination of microorganisms because there was no evidence of growth. In addition, the controls were performed at different times to guarantee randomization, and at all times, the controls were found to be sterile. Likewise, each chromatogram was analyzed independently, and the matches with the libraries were as rigorous as possible. A possible explanation, at least in the case of _M. furfurfur_, is that proper purification of the controls was not obtained in previous studies. Some volatiles have also been reported for _M. furfurfur_. Thus, our results indicate the possibility that in the work reported by our coauthors, some compounds were incorrectly reported to be present in the volatile profile of _M. furfurfur_. Supplementary Table S1 summarizes the volatile compounds identified in our controls. Considering that for _Malassezia_ species, there is no information on the biogenic source of volatiles, we hypothesized that the metabolic differences found in these yeasts might be related to lipid metabolism because degradation of fatty acids is one of the pathways by which volatiles are produced [16]. For instance, intermediates of fatty acid metabolism are precursors of VOCs, such as alkenes and alcohols [16], emitting most _Malassezia_ species in both growth phases tested. It is important to highlight that these intermediates include acetyl-CoA [51]. This important molecule participates in the modification of fatty acids by _Malassezia_[6], so the intake and metabolism of fatty acids are potential precursors of VOCs for these lipid-dependent yeasts. Figure 6 suggests different possible pathways by which VOCs are produced. The complex metabolism of these yeasts could be involved in VOC production, as has been reported for other microorganisms, such as bacteria. Lactic acid bacteria produce VOCs, such as 3-methylbutan-1-ol and 2-methylbutan-1-ol, by enzymatic conversion of branched-chain amino acids [16]. These compounds are identified in all species of _Malassezia_ in higher proportions. It is possible that during the production of these compounds by _Malassezia_, the oxygen condition decreases during static headspace sampling, forcing the yeast to use alternative pathways to metabolize glucose. Consequently, VOCs generated by anaerobic metabolism are emitted by all species. These compounds have also been reported in _Trichoderma_ species and are important in plant development [52]. Butane-2,3-dione is produced in a similar manner, being emitted under conditions of low oxygen content in bacteria [16]. It is produced by _M. restricta_ and _M. sympodialis_ in the exponential phase. These findings are interesting since all three species produced CO2 as part of their aerobic glucose assimilation, so it is daring to think that when these yeasts consume oxygen in a closed atmosphere, they start metabolizing glucose through other pathways.