Extraction, characterization, and toxicity evaluation of levan from marine bacterium Priestia aryabhattai LEV207...

Levan is an exopolysaccharide produced by microorganisms and has potential uses in the food and medical sectors. However, in natural habitats, its production is limited by nutrient scarcity and unfavorable environmental conditions. The present study is focused on enhancing levan production via a factor-by-factor optimization approach using the marine isolate Priestia aryabhattai LEV207. The impact of different media components and culture conditions on levansucrase production and bacterial cell growth was systematically investigated. Sucrose and yeast extract were identified as key inducers for levansucrase synthesis. The optimum conditions for maximum enzyme activity were 30 °C and pH 5.0, in the presence of 100 mM CaCl₂ as salt. The highest enzyme activity (404.73 µmol/mL/min) was observed in a medium containing 50% sucrose and 0.5% yeast extract after 48 h of incubation. The levan (EPSPAL207) was purified with Sevag reagent and dialysis. This optimization approach increased the product yield approximately ninefold, yielding 60.82 g/L of levan. The EPSPAL207 was characterized by NMR, XRD, and FTIR. Thermal analysis by DSC indicated high thermal stability with a melting temperature of 282 °C. EPSPAL207 exhibited a 69.16% water retention capacity and an 87.73% water solubility index. EPSPAL207 also demonstrated good antioxidant activity against ABTS (54.74%), DPPH (66.65%), and Hydroxyl (53.34%) radicals at a concentration of 20 mg/mL. Chemical hydrolysis confirmed that EPSPAL207 is a homopolysaccharide composed of fructose monomers. EPSPAL207 promoted the growth of Lactobacillus rhamnosus, a probiotic microorganism, suggesting potential prebiotic activity. The brine shrimp nauplii toxicity study indicated that EPSPAL207 exhibits low toxicity. These outcomes highlight P. aryabhattai LEV207 as a promising microbial source for high-yield levan production.