Biodegradation Of Crude Oil Using Pseudomonas Aeruginosa Under High Saline Condition

With the rapid demands and transportations of crude oil, oil spills have frequently occurred and put enormous pollution into the marine environment. The spilled oil are slowly degraded due to the low bioavailability as well as the harsh saline environment for the microorganism. In these situations, the most important requirement for bioremediation is the presence of hydrocarbon-degrading microorganisms, which could survive in the high saline environment and produce biosurfactant.Pseudomonas aeruginosa ZJU is such a typical hydrocarbon-degrading microorganism used for biodegradation of crude oil in the wastewater or contaminated soil. Therefore, P. aeruginosa with high ability of crude oil degradation and rhamnolipid production and surviving in high salinity condition should be preferred for practical application in seashore or in the sea.This thesis can be divided into the following sections:First, we reviewed the treatments of the spilled oil and the advantages of Pseudomonas aeruginosa for biodegradation, as well as the use of Pseudomonas aeruginosa in biodegradation. At the end of this section, the research outline was illustrated for selecting a strain of Pseudomonas aeruginosa to study its characteristics of rhamnolipid production and crude oil biodegradation under high salinity environment, as well as the factors determining the biodegadation process.Secondly, P. aeruginosa ZJU was acclimated by using the S35 synthetic seawater, then the acclimated P. aeruginosa ZJU (named P. aeruginosa ZJU-X) was separated. By comparing the cell growth and rhamnolipid excretion between P. aeruginosa ZJU-X and P. aeruginosa ZJU, we concluded P. aeruginosa ZJU-X could survive in the high salinity condition. However, the high concentration of Ca²⁺ and Mg²⁺ showed negative effect on the cell growth and rhamnolipid production. P. aeruginosa ZJU-X could obtain a maximal productivity of rhamnolipids at 14.6g/L,11.8g/L and 10.8g/L in vegetable oil-culture medium varied with high salinity of 25‰,35‰ and 40‰, respectively.Then, the characteristics of the rhamnolipids were analyzed. The rhamnolipidsproduced by P. aeruginosa ZJU-X were identified with two major components, Rha-Q(10)C(10) and Rha-Rha-C(10)C(10). The Critical Micelle Concentration (CMC) of the cell-free culture 24.4mg/L. The crude oil emulsification ability of rhamnolipid curlture broth was much better than the chemical surfactant sodium dodecyl sulfate (SDS).Last, the effect of salinity and the concentration of crude oil on the biodegradation were investigated. The extent of biodegradation of crude oil declined with the increase of salinity and the concentration of crude oil. When the concentration of crude oil was below 0.5%(w/v), P. aeruginosa ZJU-X could degrade a majority components of the crude oil. However, the degradation of crude oil was largely inhibited with crude oil concentration over 1.0%(w/v). By analysis of the residual crude oil, we concluded that P. aeruginosa ZJU-X degraded crude oil more thoroughly than P. aeruginosa ZJU at high saline environment.