Characterizaion Of A Pseudomonas Aeruginosa Isolate Producing High Level Rhamnolipids And Observation Of Widespread Bacterial Antagonisms In Environmental Niches

Petroleum leaks and spills are often linked to accidents resulting from activities related to the petrochemical industry involving oil drilling rings,transportation tankers and pipelines,and storage reservoirs.Chemically synthesized surfactants are routinely used for removal of petroleum pollutants.However,most chemically synthesized surfactants are only partially and slowly biodegraded by the environmental microbes,some of which are known to be toxic to animals,ecosystems,and humans.Biosurfactants are surface-active amphiphilic compounds produced by living cells and provide a promising alterative to chemically synthesized surfactants,since they are low toxicity,high biodegradability and ecological safety.Rhamnolidis are most effective biosurfactants help to remove the pollutional oil,they can emulsify the oil which could be degraded quickly by microbes.We obtained a strong rhamnolipid producer P.aeruginosa Zsl isolate derived from petroleum sludge in Zhoushan islands.Cell-free supernatant from the isolate Zsl culture exhibits 100%emulsification index against crude oil and reduces surface tension to 26.5 mN/m when using glucose as the solo carbon source.LC-MS/MS analysis indicates that the rhamnolipids produced by the Zsl isolate consist of 19 rhamnolipids(RL7-11)which include 7 monorhamnolipid homologues and 12 dirhamnolipids.Rhamnolipids RL7-11 produced by P.aeruginosa Zsl exhibit higher efficacy and stability over a wide range of pH,salinities and temperatures compared to these of the synthetic surfactant SDS,respectively.Yield of the rhamnolipids in cell-free supernatant of the P.aeruginosa Zsl cultures can reach 44 g/L when cultivated in MSM medium supplemented with 4%glucose in a shaking flask at 30℃ for 5 days.We also found different kinds of microbes enriched when cultivated in MSM+YE medium and MSM+Glu medium.Pseudomonas sp was found predominant in the sludge-derived microbes cultivated in MSM+Glu medium.In contrast,Alcaligenes sp,Donghicola sp and Bacillus sp possed the advantage when cultivated in MSM+YE medium.Co-cultivation analysis and T-RFLP analysis indicate that Pseudomonas sp would inhibit the growth of Donghicola sp and Bacillus sp.However,Alcaligenes sp would inhibit the growth of Pseudomonas sp when cultivated in MSM+YE medium.In general,our results reveal a widespread phenomenon of antagonism in major microbial populations originated from oil sludge.We propose that selection of adequate microbial strains for in situ bioremediation is essential for efficient clean up of pollutants.