Conversion of Agroindustrial Wastes to Rhamnolipid by <i>Enterobacter</i> sp. UJS-RC and Its Role against Biofilm-Forming Foodborne Pathogens

Abstract

Rhamnolipid is the main group of biosurfactants predominantly produced by <i>Pseudomonas aeruginosa</i>, a ubiquitous and opportunistic pathogen, which limits its large-scale exploitation. Thus, cost-effective rhamnolipid production from a newly isolated nonpathogenic <i>Enterobacter sp</i>. UJS-RC was investigated. The highest rhamnolipid production (4.4 ± 0.2 g/L) was achieved in a medium constituting agroindustrial wastes (sugarcane molasses and corn steep liquor) as substrates. Rhamnolipid exhibited reduced surface tension to 72-28 mN/m with an emulsification index of 75%. The structural analyses demonstrated the presence of methoxyl, carboxyl, and hydroxyl groups in rhamnolipid. Mass spectra indicated eight rhamnolipid congeners, where dirhamnolipid (<i>m</i>/<i>z</i> 650.01) was the dominant congener. Rhamnolipid inhibited biofilm formation of <i>Staphylococcus aureus</i> in a dose-dependent manner, supported by scanning electron microscopy disclosing the disruption of the microcolony/exopolysaccharide matrix. Rhamnolipid's ability to generate reactive oxygen species has thrown light on the mechanism through which the killing of test bacteria may occur.