Biopolymer production optimization, characterization and determination of biological activities from halophilic fungi

Polysaccharides produced by fungi adapted to extreme conditions are attracting significant biotechnological interest due to their diversity and distinct molecular structures. This study used the Box-Behnken design to optimize exopolysaccharide (EPS) production from two fungi isolated from hypersaline environments. Total carbohydrate and protein content, as well as the presence of uronic acid, were determined for the partially purified EPS using dialysis membrane. The helical structure of the polysaccharide chains was analyzed by the congo red test. Structural and functional group analyses were performed using NMR and FT-IR, monosaccharide composition was analyzed by HPLC, molecular weights were determined by GPC analysis, and surface morphology and elemental composition were examined using SEM-EDS analysis. Biological activity studies evaluated the antimicrobial and antioxidant activities as well as the cytotoxic effects on cells. The amounts of EPS produced under optimized conditions with two halophilic/halotolerant isolates, Rhodotorula dairenensis and Penicillium allii, were determined 2.61 g/L and 3.00 g/L, respectively. It was found that uronic acid was present in both EPS and the polysaccharide chains had a helical structure. NMR and FT-IR analyses revealed that the EPSs were in β-configuration and identified their functional groups. The EPS from R. dairenensis contained xylose, EPS from P. allii contained mannose and galactose. The highest molecular weight fractions were determined to be 2126 kDa in R. dairenensis and 218 kDa in P. allii. EDS analysis detected sulfur. While antimicrobial activity was not observed in the biological activity studies, antioxidant activity was identified. The MTT assay confirmed that the EPSs did not exhibit cytotoxic effects on cells. The EPSs from R. dairenensis and P. allii, with their features such as the presence of uronic acid and sulfur groups in their structure, helical conformation, antioxidant activity, and non-toxic effects on healthy cells as demonstrated by the MTT test, may be potential biopolymer candidates for use in the health and cosmetic industries. They are also thought to be suitable for applications such as bioremediation or heavy metal removal in hypersaline conditions. However, further detailed research is needed on the subject.