Factors affecting biosurfactant production by oil degrading Aeromonas spp. isolated from a tropical environment

An Aeromonas spp. was isolated from tropical estuarine water. The organism grew on crude oil and produced biosurfactant that could emulsify hydrocarbons. The peak growth and biosurfactant production was on the 8th day. The organism grew on a range of hydrocarbons that include crude oil and hexadecane while no growth was recorded on some hydrocarbons that include benzene. The biosurfactant produced by the organism emulsified a range of hydrocarbons with diesel (E24=65) as the best substrate and hexane (E24=22) as the poorest. After purification, the biosurfactant was found to contain about 38% carbohydrate and an unidentified lipid. No protein was present in the purified biosurfactant. Production of biosurfactant was highest in medium with glucose and lowest in the medium with diesel+acetate. Soybean was the best nitrogen source for biosurfactant production. The activity of the biosurfactant was enhanced optimally at NaCl concentration of 5%, pH of 8.0 and temperature of 40 degrees C. The biosurfactant retained 77% of its original activity after 120 min of exposure to heat at a temperature of 100 degrees C. Biosurfactant may be produced with this organism using non-hydrocarbon substrates such as glucose and soybean that are readily available and would not require extensive purification for use in food and pharmaceutical industries.