Characterization of Exopolysaccharide Produced by Pseudomonas sp. PFAB4 for Synthesis of EPS-Coated AgNPs with Antimicrobial Properties

Thermal ecosystems like hot springs are exclusive habitat of thermotolerant microorganisms that produce exopolysaccharides (EPS). In this study, EPS produced by a hot spring origin Pseudomonas species is structurally elucidated.The EPS is highly thermostable (T-d 289.98 degrees C), has low molecular weight (1510 Da) and is rhamnoglucose type consisting alpha-(1 -> 3) linked to L-Rhap and alpha-(1 -> 6) linked to d-Glc substituted with O-acetyl groups. Irregular EPS sheets with smooth surface were observed that signify the compact structure of the biopolymer; a characteristic plasticized film-like feature. Intra- and inter-molecular aggregation of EPS units are observed in atomic force microscopy. The EPS showed good rheological property at neutral pH. EPS-mediated green synthesis of silver nanoparticles (AgNP) was performed using co-precipitation method. Size of individual AgNPs had a Z-average of 93.6 nm and 0.437 polydispersity index. The EPS-coated AgNPs were moderately monodisperse. These AgNPs also exhibited biocidal property preferentially against gram negative bacteria and some fungi. Incorporating EPS to the metal nanoparticles confers them biocompatibility. Green synthesis of silver nanoparticles has gained considerable attention for its eco-friendliness in nano-medicine and nano-biotechnology. Keeping in context, the results of our study will support a new polysaccharide-mediated green synthesis approach of metal nanoparticles that shows profound antimicrobial property.