Valorization of agro-industrial waste for rhamnolipid production, its role in crude oil solubilization and resensitizing bacterial pathogens

Abstract

A bacterium, identified as Planomicrobium okeanokoites designated as strain IITR52 was isolated for biosurfactant production using corncob and pineapple waste. The surfactant produced by strain IITR52 reduced the surface tension (45 N/m) and forms an emulsion (57%). Fourier Transformed Infrared Spectroscopy analysis identified it as a rhamnolipid that exhibits thermo-stable and halo-tolerant properties. The biosurfactant exhibited stability across pH (2.0–13.0), temperature (25–121 °C) and salt concentrations (2%–17% NaCl). The strain IITR52 produced 568 and 304 mg/L of rhamnolipid in the presence of 5% treated corncob and pineapple shell syrup. The purified biosurfactant increased 2.34 folds aqueous solubility of petroleum hydrocarbons as compared to control. The purified rhamnolipid exhibited antibacterial potential against gastrointestinal (GI) and oral pathogens namely Yersinia enterocolitica MTCC 859, Clostridium perfringens MTCC 450, and Streptococcus mutans MTCC 497, Neisseria mucosa MTCC 1772 inhibiting 56%, 70%, 68%, and 77% growth respectively. At a minimum inhibitory concentration (MIC) of 6 mg/mL the rhamnolipid led to an increase in the extracellular release of DNA and protein contents. The characterized rhamnolipid showed synergistic bactericidal potential when used at 1/3 and 1/6 MIC concentrations in combination with penicillin antibiotic. Thus, waste derived rhamnolipid from an environmental isolate can serve as a promising candidate to be used as an antibacterial agent for the inhibition of pathogenic bacterial growth.