Characterization of Exopolysaccharides Having Potential Antiviral Properties from Priestia Aryabattai Strain MK1 and Bacillus sp. Strain MK2.

Viral diseases are a serious threat to humans while the most antiviral drugs have low efficiency and side effects on human health. Therefore, using microbial biopolymers as the drugs alternate to treat viral infections seems cost-effective and human friendly option. In the present study, thirty-four exopolysaccharides (EPSs) producing bacteria were isolated, and EPSs production capacity of five salt-tolerant isolates was determined under 0, 100 and 150 mM NaCl. Among these, two isolates exhibiting high anti-coliphage activity were identified through 16S rRNA gene analysis. Moreover, the EPSs were characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis, and their composition was determined. Five salt-tolerant bacteria (MK1, MK2, MK10, MK22 and MK29) exhibited higher production of EPSs at 100 mM NaCl compared to that under non-saline control. At 100 mM NaCl, the yield of EPSs ranged between 105 and 330 mg 100 mL broth. The EPSs produced by the isolates MK1 and MK2 exhibited higher anti-coliphage activity (plaque forming unit decreased from 43 × 10 mL to 3 × 10 and 4 × 10 mL, respectively), and were comprised of glucose, fructose, galactose, sucrose, lactose and xylose sugars. FTIR spectroscopy depicted that EPSs are mainly composed of hydroxyl, aliphatic, carboxyl, sulfate and phosphate functional groups, which could have bound coliphage and thus conferred higher anti-coliphage activities to the EPSs. Phylogenetic analysis revealed that MK1 and MK2 isolates formed clades within genus Priestia and Bacillus sequences, respectively. High EPSs production capacity of bacterial isolates under saline condition and high anti-coliphage activity of the EPSs implies that bacterial biopolymers could be useful in antiviral drugs therapy.