Crude biosurfactant from thermophilic Alcaligenes faecalis: Feasibility in petro-spill bioremediation

Abstract

The thermophilic bacterium Alcaligenes faecalis isolated from the crude oil contaminated soil of Upper Assam, India. The isolated bacterium was first screened for the ability to produce biosurfactant. The strain growing at 42 °C could produce higher amount of biosurfactant in medium supplemented with 2% (v/v) diesel as sole source of carbon and energy. Biochemical characterizations including FT-IR and MS studies suggested the biosurfactant to be glycolipid. Tensiometric studies revealed that the biosurfactant produced by the bacterial strain could decrease the surface tension ( σ) at air–water interface from 71.6 to 32.3 mNm −1 after 96 h of growth on hydrocarbon and possessed a low critical micelle concentration (CMC) value of approximately 38 mgl −1, indicating high surface activity. The culture supernatant containing the biosurfactant was found to be functionally stable at varying pH (2–12), temperature (100 and 121 °C) and salinity (1–6% NaCl, w/v) conditions. Both the culture broth and the cell free supernatant exhibited high emulsifying activity against the different hydrocarbons and the crude oil components. The increase in cell surface hydrophobicity and glycolipid production by the strain suggested the existence of biosurfactant enhanced interfacial uptake of the hydrocarbons. Moreover, the partially purified biosurfactant exhibited antimicrobial activity by inhibiting the growth of several bacterial and fungal species. The strain represented a new class of biosurfactant producers and could be a potential candidate for the production of glycolipid biosurfactant which could be useful in a variety of biotechnological and industrial processes, particularly in the oil industry.