Optimization Of Fermentation Conditions By Pseudomonas Aeruginosa And Studies On Characters Of Rhamnolipid

Rhamnolipid is a highly effective biosurfactant,which can significantly reduce the interfacial tension and has good emulsification.It also can promote the degradation of hydrophobic substrates(alkanes,oils and fats),and it is low toxicity,high biodegradability and environment-friendly.The characteristics of this product have a broad application prospect in the remediation of marine crude oil pollution.In this paper,the study of Pseudomonas aeruginosa fermentation to produce rhammolipid was carried out,and the culture medium and fermentation conditions were optimized by shaking flask experiment.Then we used a 7.5-L fermentor to conduct a small test fermentation,to optimize the fermentation process,to establish a small fermentation kinetics model,and finally study the Physicochemical properties,the main findings are as follows:The single-factor experiment was established,which basic medium with corn oil as the carbon source,sodium nitrate as the nitrogen source,and Na2HPO4:K2HPO4(3:2)as the phosphorus source.Three significant factors affecting the yield of rhamnolipid were screened by Plackett-Burman design:nitrogen source concentration,phosphorus source concentration,and inoculum size.The steepest climbing experiment was used to determine the center point of the response surface analysis.Finally,the significant influence factors were modeled and analyzed by response surface analysis to determine the best.Medium formulation(g/L):corn oil 50.0;NaN037.15;Na2HP04 4.99;K2HPO4 3.32;MgS04-7H20 0.4;CaCl2 0.01;pH 7.0;trace element solution 4 mL/L(trace element solution composition:FeSO4·7H2O 18 g/L,ZnSO4·7H2O 3.0 g/L and MnSO4·2H2O 3.0 g/L),and the inoculation amount was 2.71%.On this condition,the rhamnolipid output was 49.386 g/L,4.74 times as much as before the optimization.On the basis of the previous shaking flask experiment,a fermentation test was conducted in a 7.5-L fermentor.At the fermentation temperature of 30℃,the stirring speed of 400 r/min,and the ventilation rate of 3 L/min,rhamnolipid can reach a high yield of 38.129 g/L,the fermentation time required to reach the highest yield is 96 hours,which is 12 hours shorter than shake flask fermentation.Through the pH and DO changes of fermentation broth during fermentation,it is concluded that Pseudomonas aeruginosa has a higher fat-producing rate under the condition of sufficient oxygen and weak alkalinity.Based on Logistic,Luedeking-Piret and other equations,a kinetic model for the cell growth,product synthesis,and substrate consumption of Pseudomonas aeruginosa Zsl during the process was established.The fitting effect of the three equations is good,and the fermentation process can be well simulated,which has certain guiding significance for further optimization of fermentation methods in small tanks in the future.Separation and purification of fermentation products to obtain brown paste rhamnolipid crude extract.The crude rhamnolipid had a CMC value of 0.116 g/L and a surface tension of 29.12 mN/m at CMC,which was superior to the chemical surfactant SDS.In extreme salinity,temperature,and pH value,rhamnolipid has lower surface tension than SDS.Salinity and temperature have little effect on the surface tension of crude rhamnolipid.Under extreme acidic conditions(pH=2),the surface tension increased slightly.In general,the rhamnolipid crude product has good stability under extreme conditions.