## 5 Conclusions  
This study demonstrates the necessity of the continuous deciphering of promising antifungal metabolites from natural sources. Herein, a soil isolate exhibited promising antifungal activities against _Candida albicans_ and _A. niger_ was identified as _Bacillus toyonensis_ OQ071612. The produced antifungal metabolite exhibited promising fungicidal properties and stability within a pH range of 6-7, temperatures of up to 50 \({}^{\circ}\)C, and in the presence of various surfactants, detergents, and enzymes. The antifungal molecule was chemically identified as 6-methoxy-1H-Indole-2-carboxylic acid, using advanced spectroscopic techniques. Its production was statistically optimized using response surface methodology (RSM) with a central composite design, resulting in an approximately 3.49-fold increase. This is the first report on the production optimization of the respective chemical moiety from _Bacillus toyonensis_ against human fungal pathogens. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/microorganisms11122835/s1](https://www.mdpi.com/article/10.3390/microorganisms11122835/s1)]([https://www.mdpi.com/article/10.3390/microorganisms11122835/s1](https://www.mdpi.com/article/10.3390/microorganisms11122835/s1)), Figure S1: Cross-streak method of isolate (F1) against _Candida albicans_ ATCC10231; Figure S2: Dual culture technique showing inhibitory effect of the isolate (F1) against _A. niger_, (a) shows clear zone between the edges of fungal mycelia and bacterial colonies. (b) shows the control, inoculated with _A. niger_ without streaked bacteria. (c) is the control, showing the diffuse growth of _A. niger_ in the presence of a non-productive bacteria; Figure S3: Molecular phylogenetic analysis of the query isolate _Bacillus toyonensis_ OQ071612 strain (F1) using the maximum likelihood method based on the Tamura-Nei model in MEGA X; Figure S4: Effect of incubation time on the yield of the antifungal metabolite produced by _Bacillus toyonensis_OQ071612 against _Candida albicans_ ATCC0231; Figure S5: Average inhibition zones of the tested intracellular and extracellular antifungal metabolite(s) produced by _Bacillus toyonensis_ OX071612 against _Candida albicans_ ATCC0231; Figure S6: The bioautography method was used to determine the antifungal activity of the pooled fractions obtained from column chromatography fractionation against _C. albicans_. Plate (a) highlights the zone of inhibition caused by the fractions of the _B. toyonensis_ metabolite with the most potent antifungal activity. Plate (b) shows the control plate; Figure S7: Visualization of the most active pooled fractions of the antifungal metabolite of _B. toyonensis_ isolate OQ071612 under a UV lamp (UVitec(r) at 365 nm (a) and at 254 nm (b); Figure S8: HPLC chromatogram of the isolated compound; Figure S9. Positive ESI-MS spectrum analysis of the isolated compound; Figure S10: The relationship between the inhibition zones against _Candida albicans_ ATCC0231, corresponding to various antifungal metabolite concentrations; Figure S11: The relationship between the UV absorbance at \(\lambda\)max at 273 nm and various concentrations of antifungal metabolite in \(\mu\)g/mL. Conceptualization, S.E.E.-S, N.A.A., A.A.A., M.Y.A., G.S.E.-H. and K.M.A. ; methodology, S.E.E.-S., N.A.A., G.S.E.-H. and K.M.A. ; validation, G.S.E.-H., N.A.A. and K.M.A. ; formal analysis, S.E.-S. and G.S.E.-H.; investigation, G.S.E.-H., N.A.A. and K.M.A. ; resources, A.A.A., M.Y.A. and K.M.A. ; data curation, N.A.A., G.S.E.-H. and K.M.A. ; writing--original draft preparation, S.E.E.-S.; writing--review and editing, G.S.E.-H., N.A.A., A.A.A., M.Y.A. and K.M.A. ; supervision, G.S.E.-H., N.A.A. and K.M.A. ; funding acquisition, A.A.A., M.Y.A. and K.M.A. All authors have read and agreed to the published version of the manuscript.