Characterization of exopolysaccharides having potential antiviral properties from Priestia aryabattai strain MK1 and Bacillus subtilis strain MK2

Abstract Viral diseases are a serious threat to human life while most antiviral drugs have low efficiency and side effects on human health. Therefore, scientists are interested in using microbial biopolymers as the drugs alternate to treat viral infections. In the present study, thirty-four exopolysaccharide producing bacteria were isolated, and exopolysaccharide production capacity of five salt-tolerant isolates was determined under 0, 100 and 150 mM NaCl levels. The two isolates exhibiting high anti-coliphage activity were identified through 16S rRNA gene analysis. Moreover, the exopolysaccharides were characterized by FTIR and XRD analysis, and their composition was determined. Five salt-tolerant bacterial isolates viz. MK1, MK2, MK10, MK22 and MK29 exhibited increased production of exopolysaccharides at 100 mM NaCl compared to the non-saline control. At 100 mM NaCl, the yield of exopolysaccharides produced by five isolates ranged between 105 and 330 mg 100 mL− 1 broth. The EPSs produced by the isolates MK1 and MK2 exhibited higher anti-coliphage activity (PFU decreased from 43×106 mL− 1 to 3×106 and 4×106 mL− 1, respectively). The sugar profile of EPS produced by MK1 and MK2 was comprised of glucose, fructose, galactose, sucrose, lactose and xylose in variable proportions. FTIR spectroscopy depicted that exopolysaccharides are mainly composed of hydroxyl, aliphatic, carboxyl, sulfate and phosphate functional groups. XRD analysis indicated that EPS had an amorphous structure with crystalline index (CIxrd) ranging between 0.33 and 0.39. Phylogenetic analysis revealed that MK1 and MK2 isolates formed clades within genus Priestia and Bacillus sequences (16S rRNA), respectively. High EPS production capacity of bacterial isolates under saline condition and high ant-coliphage activity of the EPS implies that bacterial biopolymers could be useful in antiviral drugs therapy.