Identification of novel Gramicidin S analogs from Aneurinibacillus aneurinilyticus isolated from corn steep liquor with potential antifungal activity

In the existing literature, there is ample information available concerning the analogs constituting linear Gramicidin (Gramicidin A). However, the literature lacks information regarding the microbial production of cyclic Gramicidin S (GR-S) and the study of its analogs' amino acid composition. Thus, in this study, GR-S was produced by Aneurinibacillus aneurinilyticus, isolated from corn steep liquor (CSL) and grown in synthetic or CSL-based medium. The extract was obtained from microbial biomass and underwent analysis with ultra performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) to ascertain the presence and abundance of GR-S clusters, identifying five GR S analogs. Hence, when using a synthetic medium, the dominant cluster compromised the sequence Val-Orn-Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro. Contrarily, when using CSL-based medium, the main analog was composed of Val-Orn-Leu-Phe-Pro-Val-Lys-Leu-Phe-Pro. In the remaining analogs, one or both Ornithine (Orn) residues were replaced by Lysine (Lys) or diaminobutyric acid (D-Dab). Microscopy images revealed that the use of CSL-based medium resulted in a lower yield of GR-S and a higher accumulation of vacuoles compatible with the presence of intracellular polyhydroxyalkanoates (PHA) when comparing with TSB medium. The antifungal assay revealed a superior conidial inhibition activity of GR-S extract under evaluation against Aspergillus brasiliensis in comparison to the commercial GR-S. Consequently, it can be concluded that this novel microbial GR-S extract exhibits favorable antifungal activity, positioning it as a promising candidate for antimicrobial treatments. However, further research is necessary to address the global challenge of antibiotic-resistant pathogens.