The Mechanism Of Policing Quorum Sensing In Pseudomonas Aeruginosa PAO1

Bacterial quorum sensing is one of typical cooperative behaviors due to its regulation of public goods production.Because of public goods being shared among the local population,the cooperation regulated by quorum sensing is easy to be invasived 'by cheaters who do not produce public goods.Actually,a series of mechanisms are evolved to maintain the stability of quorum sensing,such as kin seletion,metabliosm constraint,prudent metabolism and policing control.Policing control has been proposed recently,and researches on it is extremely limited.In P.aeruginosa PAO1,cooperators employ RhlIR system to regulate hydrogen cyanide secretion and policing control the cheaters in the local population.Here,we continued to explore its mechanism,with the viewpoints from activation of policing control,self-protection of cooperators and the reponse to extral nitrogen source ammonia sulfate.This study would be help us to understand the significance of quorum sensing in further,it also would be benifical to pathogen therapy and optimization of microbiological ecosystem with the theory of quorum sensing.The main results obtained are as follows(1)The activation of policing control by ROS:The tolerance of HCN and H2O2 in social cheaters AlasR is only 12.5%and 19.3%relative to cooperator w.t.respectively.The hydrogen cyanide released by the cooperators can block the respiratory chain and induce ROS in social cheaters.This ROS not only inhibits the rapid growth of cheaters in the population but also improves the rhlR activity in cooperators.Thus the ROS acts as a signal to active the policing.In addition,ROS not only plays a role in the expression of rhlR,but also can affect PA2190 and oxyR.This mode ensures the high efficiency of polciing.(2)The self-protection of cooperator during the process of policing:RhlIR not only regulate the hydrogen cyanide secretion in cooperators to punish cheaters,but activate the expression of Cio.The expression of Cio can protect cooperators from the toxicity of HCN and do not block the electron transport in respiratory chain.The tolerance of HCN in AcioA is only 50%relative to social cheaters AlasR.And the AcioA failed in the competition with ?lasR.The expression of Cio for self-protection in cooperators is the basis of the policing quorum sensing.(3)The response of policing control to environmental factors:In comparison with the extra additional of ammonia sulfate,the population is easy to collapse under without extra additional of ammonia sulfate.The present of extral additional of ammonia sulfate could indue the expression of rhlR,inhibit the transfer from glycine to 5,10-methylenetetrahydrofolate(5,10-methylene-THF)and ammonia,enhance the synthesis of hydrogen cyanid and improve the ROS level in competition system.The improvement of the efficiency of policing control is a biochemical tradeoff in bacteria,which is one of examples for the response of policing quorum sensing to environmental factors.