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.
Highlights
Mangrove wetland ecosystems are important inter-tidal estuarine wetlands along the coastlines of tropical and subtropical regions exposed to anthropogenic contamination by polyaromatic hydrocarbons (PAHs) from tidal water, river water, and other land based sources
The strain KVD-HR42 produced excessive amounts of foam when grown on crude oil containing mineral salts media (MSM) and surface tension reduction (STR) indicates the ability of a biosurfactant to remove oil from mangrove sediments by reducing the capillary force responsible for holding crude oil and soil together (Calvo et al, 2009)
19 to 20% of isolates from the crude oil contaminated sediments were biosurfactant producers. These results may be attributed to the fact that high concentrations of crude oil did not select for bacteria able to produce biosurfactants
Summary
Mangrove wetland ecosystems are important inter-tidal estuarine wetlands along the coastlines of tropical and subtropical regions exposed to anthropogenic contamination by polyaromatic hydrocarbons (PAHs) from tidal water, river water, and other land based sources. Mangrove’s exceptional features of high primary productivity, abundant detritus, rich organic carbon, and reduced conditions make them a preferential site for uptake and preservation of PAHs from anthropogenic inputs (Bernard et al, 1996). Such catastrophes make this preserved marine environment highly susceptible to an ecological catastrophe. Efficient strategies must be developed to monitor oil spills in such environments especially in pristine mangrove wetland ecosystems (Santos et al, 2011). Successful bioremediation of oil contaminated environment still remains a great challenge for the researchers (Perfumo et al, 2010). The principle processes for their successful removal are currently believed to be microbial transformation and degradation (Gibson et al, 1975)
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