Rhamnolipid biosurfactant production by Pseudomonas aeruginosa strain KVD-HR42 isolated from oil contaminated mangrove sediments

Abstract

Pseudomonas aeruginosa strain KVD-HR42 exhibiting growth and biosurfactant production with 1% molasses as the sole carbon source was isolated from oil contaminated mangrove sediments. Optimization of media conditions involving variations in carbon, nitrogen sources, amino acids, pH, temperature, and NaCl% were evaluated with the aim of increasing biosurfactant productivity and surface tension reduction (STR). The highest biosurfactant production of 4.83 g/L was obtained when cells were grown in mineral salts media (MSM) supplemented with 1% (w/v) molasses, NaNO3, and leucine 0.1% (w/v) at 35±2°C at 150 rpm after 48 h. The results obtained from kinetics study indicated that biosurfactant production, E24%, and rhamnose concentration were growth associated. However, maximum biosurfactant production occurred in the exponential growth phase and detected an increase in E24% and rhamnose concentration. The Fourier transform infrared (FTIR) spectra confirmed the rhamnolipid nature of the biosurfactant. Stability studies revealed the thermostable activity of biosurfactant (110°C for 15 min) and could also withstand wide pH and NaCl ranges. Maximum oil biodegradation of 68% was achieved with 1% waste lubricant oil (WLO). The biosurfactant emulsified various hydrocarbons with varied efficiencies. However maximum E24% and E48% activity was exhibited with n-hexadecane (69.5 and 40%). The results reveal the potential of strain KVD-HR42 biosurfactant for the bioremediation of petroleum hydrocarbons in mangrove sediments. Key words: Pseudomonas aeruginosa, surface tension, molasses, crude oil, emulsification activity, biodegradation.