## 4 Discussion
The volatiles assayed in this study were selected on the basis of their fungistatic or fungicide activity, which can generate physiological stress at low concentrations. These substances were also chosen because of their commercial availability [26]. According to our results, the concentrations of these substances assayed (lower than MIC) probably exerted a kind of pressure on the metabolism of _A. aureus_,which was reflected in the accumulation of biomass and RV. According to our data, the assayed concentrations of elicitors did not affect cell viability. To the best of our knowledge, this is the first work showing the effect of volatiles on the production of RV. Limonene and camphor did not produce a statistically significant increase in RV, whereas menthol caused a dramatic reduction in RV concentration. This result may be correlated with the strong antifungal activity of menthol, which was observed in the broth microdilution tests (Table 1). Due to the latter fact, these volatiles were discarded in further experimentation. On the contrary, citral (a mix of isomers) and thymol stimulated the production of RV, with levels of 187.8 \(\pm\) 2.2 mg L\({}^{-1}\) and 162.7 \(\pm\) 4.1 mg L\({}^{-1}\), respectively. According to these results, citral and thymol were able to increase RV production by around 40%, and the biomass by around 25% in comparison with the control batch cultures. Glucanex, which is a mixture of \(\beta\)-1, 3 glucanases (with optimal activity at pH 7), produced the best accumulation of RV (198.3 \(\pm\) 7.6 mg L\({}^{-1}\); \(>\)50%), with significant biomass accumulation (230.6 \(\pm\) 3.8 g L\({}^{-1}\); \(>\)20%). This evidence suggested that the biosynthesis of RV in _A. aureus_ is stimulated by enzymes with antagonist activity produced by fungal competitors [27]. The induction of biomass by Glucanex, thymol, and citral may be produced as an alternative defense of _A. aureus_ to ameliorate the stress caused by these substances. Previous studies suggest that some volatiles and specific enzymes are able to increase fungal biomass [24]. The best variables were reassessed in batch cultures with optimal temperatures, pH, amino acid precursors, and the three more effective elicitors for RV production. Glucose levels decreased gradually and were negligible at day 10, whereas biomass increased within days 7-12. This fact strongly suggests that the carbon source was used for both the accumulation of biomass and the production of RV. The consumption of TYR was completed at day 9 for cultures containing both volatiles and at day 8 for those containing Glucanex, suggesting that the hydrolytic enzymes of Glucanex stimulate the use of TYR for conversion into RV. This fact was endorsed by the highest accumulation of RV in these cultures. The same results demonstrate that the production of RV in _A. aureus_ can be efficiently enhanced by the combination of volatiles and isoenzymes with \(\beta\)-1, 3 glucanase activity to generate 225-237.6 mg L\({}^{-1}\) RV, which represents almost twofold higher RV concentration than that reported in a previous work [14]. _A. aureus_ MaC7A produced 0.23 g L\({}^{-1}\) RV, which is a better amount than that reported by recombinant yeasts that produce RV from _p_-coumaric acid (0.04 g L\({}^{-1}\) RV) [1].