Production and biological activities of exopolysaccharides synthesized by thermophilic bacilli isolated from hot springs in Türkiye.

Thermophilic bacteria able to produce exopolysaccharides (EPSs) have become attractive in recent years. EPSs synthesized by thermophiles are worth investigating due to their unexplored structural and biological properties. In this study, EPSs from thermophilic, Gram-positive bacterial isolates were purified and tested for their biological activities. A total of one hundred seven thermophilic bacteria were screened for their ability to produce exopolysaccharides. Nine isolates belonging to Geobacillus, Parageobacillus, Aeribacillus, and Anoxybacillus genera with highest EPS production were chosen, and purified EPSs (20, 61, 74, 76, 78, 89, 106, 134, and 261) were used for biological activity studies. EPS yields of selected thermophilic bacteria ranged between 117 and 419 mg/L. Among the tested EPSs, 61, 106, and 261 showed antibacterial effect against E. faecalis JH2-2 at a final concentration of 1.5 mg/mL. EPS samples had significant antioxidant capacity, especially EPS 134, with the highest DPPH radical scavenging activity of 100% at a concentration of 5 mg/mL and the strongest reducing power. EPS 20 showed the highest lipid peroxidation inhibition effect at a rate of 31%. EPSs displayed weak alpha-amylase inhibition activity when compared with standard acarbose. The prebiotic indices of EPSs 20, 61, 76, 89, 134, and 261 were found to be higher than that of inulin, a representative prebiotic carbohydrate for all tested lactic acid bacteria in the study. All examined EPSs inhibited the biofilms formed by various bacteria depending on the test strain. Results indicated that thermophilic EPSs had remarkable antioxidant, prebiotic, and antibiofilm activities. Therefore, EPSs characterized in this study may have technological applications in health and food fields.

Characterization and biological activities of a novel exopolysaccharide produced from Geobacillus thermodenitrificans HBB 111 strain.

In this study, EPS production conditions of Geobacillus thermodenitrificans HBB 111, a thermophilic microorganism, were optimized and the amount of produced EPS (EPS 111) was found to be 44.0 mg/L. EPS 111 was purified using ion exchange chromatography and gel filtration chromatography, and a single type of exopolysaccharide was obtained. The structure of the purified EPS 111 was evaluated by TLC, FTIR, NMR, and GC-MS, and it was observed that it contained hexose (glucose, fructose, galactose and mannose) and pentose sugars. From the SEM photographs, it was understood that EPS 111 had an amorphous, rough, and layered structure. It was found that purified EPS 111 had low cytotoxicity (2.3%) and exhibited high antioxidant activity and remarkable antidiabetic, prebiotic and fibrinolytic activities. It is very valuable that the purified EPS 111 in this study offers multiple biological activities compared to the thermophilic EPSs reported in the literature and has a high potential for use in biotechnological and biomedical fields.