Effect From Nitrogen On The Population Stability Of Pseudomonas Aeruginosa SD-1 And Its Mechanism

Pseudomonas aeruginosa SD-1 is a highly effective heterocyclic compound-degrading strain,who plays an important role in the treatment of pollutants through bioaugmentation.The population stability of bioaugmented strains is key to stabilize operation of the bioaugmentation system.Although there has been a great deal of attentions to the interspecific competition between the bioaugmented and the indigenous strains in the ecosystem,there was few reports on the intraspecific stability of bioaugmented strains.In this study,P.aeruginosa SD-1 was used as an experimental strain to test how different nitrogen salts existing in wastewater treatment system affect the population stability of strain SD-1 by long-term evolutionary experiments.Comparing the growth of cheater to WT strain in the medium adding different nitrogen salts,the mechanism of quorum sensing that how different nitrogen salts affect the intraspecific population stability of strain SD-1 from the perspective of metabolism was elucidated.Analyzing the quorum sensing activities of evolved cooperators,the mechanism of quorum sensing that how different nitrogen salts affect the intraspecific population stability of strain SD-1 from the perspective of evolutionary was explored.This study is of great significance for enriching quorum sensing theory,extending the application of quorum sensing theory in bioaugmentation system and optimizing the operation strategy of bioaugmentation system.The main results obtained are as follows:(1)In the long-term culture,there are partial groups collapsed with 1-2 orders of magnitude decreasing of population density.The collapsed probabilities were 0%,33.3%,66.6%and 11.1%in the groups adding ammonia,nitrate,nitrite and no addition of nitrogen,respectively.In the stable group,the range of cheaters is 0%-53%.The range of cheaters in the collasped group is 51%-81%.Proteases decresed dramatically in the collasped groups.The adding nitrogen salts could influence significantly the population stability of SD-1.The population in the medium adding nitrite and nitrate collasped more easily.(2)In the short-term culture,ammonia was the most suitable nitrogen assimilation nutrient for strain SD-1,followed by nitrate.It is difficulte to use nitrite as an assimilative nutrient by strain SD-1.In the presence of nitrite and nitrite,strain SD-1 produced more 2-3 times public goods than other groups.In the glucose medium adding nitrate,the cheater obtained higher growth in the first 12 h than the WT.The growth of the cheater was significantly higher than WT in the glucose medium adding nitrite.The cooperator have a heavy metabolic burden while the cheater have high metabolic fitness in presence of nitrite and nitrate.The difference of fitness between the cheater and the cooperator was primary reason why the population collasped more easily in the medium adding nitrite and nitrate.(3)After long-term evolution,twenty-four strains were isolated from the stable population.Therea was no significant difference of growth between evolved cooperators and original cooperator.The contents of 3OC12-HSL,C4-HSL and protease of evolved cooperators were lower than that of original cooperator,which suggested that the activities of quorum sensing trend to much prudent during the evolution.However,the yield of pyocyanin of evolved strains was higher than that of original strains,which implied policing quorum sensing was improved during the evolution.Prudent evolution of cooperation and effective promotion of the policing were the important reasons for the long-term stability of population.