Characterization of a Haloalkaline Nocardiopsis sp. Strain S10 Isolated from Wastewater and Optimization of Culture Medium for Improving Production of Antifungal Compounds

Background: The emerging antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are a pressing global concern. Furthermore, the limited number of available antifungal agents requires the discovery of new antimicrobials. Introduction: This paper focused on the isolation and characterization of an actinobacterium designated S10, the study of its antimicrobial activity, on the one hand, and the optimization of antifungal production using statistical methods, on the other hand. Methods and Results: A haloalkaliphilic actinobacterium designated S10 was isolated from a wastewater treatment plant in the Souk-El-Tenine region (Bejaia, Algeria). This strain showed a broad spectrum of activity against bacteria (B. subtilis, L. innocua, M. luteus, S. aureus, MRSA, E. coli, P. aeruginosa, S. Typhi, and V. cholerae), molds (A. niger, G. geotricum, and F. oxysporum) and a pathogenic yeast (C. albicans). The extracellular enzymes producer Nocardiopsis sp. S10 was identified based on morphological, chemical, and 16S rRNA gene sequencing analysis. The best antimicrobial production was achieved on Mincer-Sea-Water (MSW) solid medium, and the antibiotics produced were extracted with ethyl acetate. For antifungal production, central composite design (CCD) and response surface methodology (RSM) were used to optimize the culture medium formulation. Conclusion: Optimal antifungal activity was achieved using a mixture of 2 g. L^-1 starch, 2 g. L^-1 of yeast extract and 2.75 g. L^-1 of peptone at pH = 9.2. The application of the statistical approach stimulated a good yield of anti-C. albicans activity, corresponding to an increase of 72.22% compared to the non-optimized conditions.