The Study Of High Rhamnolipid Production And Crude Oil Biodegradation By A Strain Of Pseudomonas Aeruginosa

Rhamnolipid secreted by Pseudomonas aeruginosa is a kind of biosurfactant with extensive use, and Pseudomonas aeruginosa is also widely used in the biodegradation of many organic pollutants. At present, various vegetable oils have been used in rhamnolipid biosynthesis. Generally, the production is 10~30 g/L and the fermentation period is around one week. Although rhamnolipid is very effective in the treatment of environmental pollution and will not be harmful to the environment, it cannot be widely used on industrial scale presently while comparing to chemical surfactants, for the consideration of economic cost. Therefore, high production of rhamnolipid with low material cost should be considered in order to apply this biosurfactant to industrial level.This thesis was divided into six sections. Section 1 reviewed rhamnolipid production and application, 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, as well as to improve its productivity of rhamnolipid and shorten its fermentation period.In Section 2, we discussed the relationship between rhamnolipid production and crude oil biodegradation after preservation in crude oil. While the strain preserved in crude oil-containing medium was transferred to glycerol medium for several passages, it expressed increased rhamnolipid productivity, which sustained for six passages and sharply decreased after the seventh passage. The rhamnolipid productivity was closely related to its biodegradability in crude oil-containing medium, which could be correspondingly sustained for six subcultures and then decreased sharply after the seventh passage. This strain could degrade many compositions in crude oil from Shengli Oil Field within a short period. The main compositions degraded were alkanes with intermediate chains and the rhamnolipidproduction in glycerol medium could reach 12.88 g/L.In Section 3, U.V. mutation was conducted to improve rhamnolipid production. After two times of U.V. mutation and the natural selection, a strain with high productivity was selected. The rhamnolipid production in glycerol medium was increased by 88.4% for the first passage and rhamnolipid accumulation was rapid. While this strain was subcultured in glycerol medium for three passages, its rhamnolipid productivity could be increased.In Section 4, the culture medium was optimized. Rapeseed oil was selected as the carbon source. After optimization, rhamnolipid production could reach 48.43 g/L within 120h. It reached to 56.1 g/L at the end of fermentation and 92.3% of rapeseed oil was used.In Section 5, rhamnolipid was produced in a bioreactor. The fed-batch fermentation was conducted and a foam recycling system was set. The strain had a rapid growth and a high cell concentration. Rhamnolipid was accumulated rapidly and the production could reach 59.28 g/L. The recovery ratio of the product was 72.9% with a purity of 76.89%.Finally, this paper was summarized in Section 5. And the genetic research of improving the rhamolipid productivity and crude oil biodegradability by preservation in crude oil, as well as rhamnolipid production by using frying oil was prospected in the end.