Sodiomyces genus is obligate alkaliphilic ascomycetous fungi of the Plectosphaerellaceae family (Grum-Grzhimaylo et al., 2016, DOI: 10.1007/s13225-015-0320-2). They prefer habitats with alkaline conditions (pH≥10) such as soda salterns and the edge of the soda lakes. Such habitats are located all over the world, although, as a rule, they are small in area. In addition to pH stress, organisms, inhabiting in soda soils, have to survive under fluctuating osmotic and temperature conditions, that vary drastically with a change of drought and rain, heat and freezing. Studies of the antimicrobial activity of alkaline fungi are rare. The prime purpose of this study was to isolate and identify antimicrobial compound from an alkaliphilic fungus Sodiomyces alkalinus. According to previously data, high level antimicrobial culture broth was obtained for three strains of S. alkalinus. Analytical separation by reversed-phase HPLC for the ethyl acetate extract was carried out according to the data described earlier (Kuvarina et al., 2021, DOI: 10.1134/S0003683821010142). It has been suggested that the molecule studied is typical to be a polypeptide; there by its initial structure analysis was conducted by automated Edman sequencing. The polypeptide production yield from the culture broth of S. alkalinus on alkaline medium was achieved in a period of fermentation in 14 days about 25.54 ± 1.4 mg/L. Searching for potential homologies amongst NCBI databases (https://www.ncbi.nlm.nih.gov/) using BLASTP algorithm led to complete matching with fungal hydrophobin F11 (GenBank: ROT36721.1/NCBI Reference Sequence: XP_028464527.1). This data was previously obtained based on whole genome sequence which has been provided for S. alkalinus F11 strain that is typical (Grum-Grzhimaylo et al. 2013, DOI: 10.3767/003158513X673080). The antimicrobial activity of the novel antifungal agent hydrophobin from S. alkalinus was studied in vitro. Strong antifungal effect was against pathogenic and opportunistic fungi strains and MIC was determined. The protein showed growth inhibitory activity of filamentous and yeast fungi. The activity of hydrophobin Sa-HB1 against Aspergillus spp. was comparable to reference polyene cyclic antibiotic Amphotericin B. The inhibition zones for all clinical Candida isolates were found to be 12-14 mm, while C. krusei, C. tropicalis were inactive to Amphotericin B. As a result, the antimicrobial compound from S. alkalinus is hydrophobin. It has high antifungal activity comparable to reference antibiotics. The hydrophobin Sa-HB1 responsible for the reported antifungal activity of S. alkalinus, and may serve as a potential source of lead compounds that can be developed as antifungal drug candidate.
This study was supported by the Russian Science Foundation (grant no. 22-25-00353)