Study On The Release Pattern Of Quorum Sensing Signaling Molecules (AHLs) For Bacteria And Their Bioaugmentation During Biofilm Formation Process

Quorum sensing(QS)is a kind of “language” for microbial communication.It can control the expression of certain genes by sensing the changes of signal molecules around the environment,thus regulating their physiological activities.It is a reflection of the microbial socialization behavior.In recent years,more and more researchers about microbiology pay attention to QS.Different microorganisms communicate with each other in different “languages”,so the chemical signaling molecules they communicate with each other are also different.Acylated homoserine lactones(AHLs)are the chemical signaling molecules used to communicate between the Gram-negative bacteria.The signaling molecules used to communicate between the Gram-positive bacteria are called diffusion signal factors(DSF).AHLs and DSF are belonging to the intraspecific signaling molecules.Auto-inducer-2(AI-2)is the interspecific signaling molecules that can make Gram-positive bacteria communicate with Gram-negative bacteria.Enhancing the biodegradation of pollutants in water by microbial quorum sensing has made an important theoretical and practical significance.The strains secreting signal molecules AHLs in activated sludge were screened,and the types and release patterns of the AHLs-secreting strain Aeromonas hydrophila(A-L2)was investigated.On this basis,the biofilm strengthening mechanism by strain A-L2 on the sensitive strains(quinoline-degrading bacteria)was explored in order to find a better way in the removal process of quinoline organic compounds in wastewater.The main results are as follows:(1)A method for screening AHLs-secreting strains by report strains was established.Four strains secreting long-chain AHLs were named as A-L2,A-L4,A-L5,A-L10,and three strains secreting short-chain AHLs were named as A-L2,A-L7,A-L8.They all screened from the activated sludge system.The strain A-L2 secreting both long-chain and short-chain AHLs was systematically analyzed,and it was identified as the member of Aeromonas hydrophila by molecular biology.(2)The AHLs signal molecules secreted by strain A-L2 were identified as N-Butyryl-L-homoserine lactone(C4-HSL)and N-Hexanoyl-L-homoserine lactone(C6-HSL),respectively.Quantitative methods of C4-HSL and C6-HSL were established,and their minimum detection and quantification limits were determined.The detection limits and quantification limits of C4-HSL were 0.1 and 0.5 ?g/L,respectively.The detection limits and quantification limits of C6-HSL were 0.7 and 1.0 ?g/L,respectively.(3)The dynamic changes of the AHLs secretion capacity,the contents of C4-HSL and C6-HSL secreted by strain A-L2 during the growth process were systematically analysed.It was found that the secretion of C4-HSL and C6-HSL was a cumulative process,and at the logarithmic growth stage,the secretion capacity of strain A-L2 reached the maximum.At 36 th h,the cumulative amounts of C4-HSL and C6-HSL reached the maximum.When peptone was used as nitrogen source,glucose was used as carbon source,p H was 7.0,incubation temperature was 35 ?,and sodium chloride was added to make ionic strength 1%,the optimal release mode of signal molecule would be achieved.(4)The mechanism of signal molecules C4-HSL,C6-HSL and their mixture during quinoline-degrading strain(Ochrobactrum sp.,LC-1)biofilm formation was analyzed.The results showed that the swimming ability of strain LC-1 could be improved by C4-HSL and C6-HSL.C4-HSL can increase the biomass of strain LC-1 and stimulate the secretion of extracellular polysaccharides while C6-HSL can induce the enhancement of the adhesion of strain LC-1 and the secretion of extracellular proteins,both of which work together to strengthen the biofilm formation process of strain LC-1.(5)The efficient degradation of quinoline was enhanced by strain A-L2 which secreted C4-HSL and C6-HSL.The results showed that the introduction of strain A-L2 could increase the content of C4-HSL and C6-HSL in the degradation system,and the content of biofilm was higher than that of the control group.It could accelerate the quinoline biodegradation and the degradation time was shortened by 12?24 h.The effect of bioaugmentation was obvious.