Influence Of The Quorum Sensing Systems On Heterotrophic Nitrification-aerobic Denitrification

Heterotrophic nitrification-aerobic denitrification(HNAD)is an efficient way of aerobic breathing and that is also essential in the earth's nitrogen-cycling.Environmental circumstances such as carbon and nitrogen resources have been confirmed to adjust this process,though how simultaneous nitrification and denitrification(SND)is modulated in a bacterial biotope is still ambiguous.Pseudomonas aeruginosa is one kind of bacterium which manipulate numerous colony behavior via quorum sensing(QS)system.The bacterium possesses at least two types of QS molecule signals:N-acyl-L-homoserine lactone(AHL)signals and 2-heptyl-3-hydroxy-4-quinolone(PQS).The influence of AHL and PQS on heterotrophic nitrification-aerobic denitrification process was investigated in this study to get knowledge of QS regulating nitrogen removal in a bacterial colony.HNAD process of P.aeruginosa was both inhibited by AHL and PQS,while lacking those two kinds of signals could enhance the ability of nitrogen removal.Measuring the nitrifying-denitrifying enzyme activities indicated that ammonia monooxygenase and hydroxylamine oxidase activity was improved by PQS,while PQS inhibited nitrite oxidoreductase,nitrite reductase,nitric oxide reductase and nitrate reductase catalyzing abilities.Besides,the absence of AHL enhanced the activities of nitrite oxidoreductase,nitrate reductase,ammonia monooxygenase,nitrite reductase and nitric oxide reductase activities,otherwise it suppressed the activity of hydroxylamine oxidase.The results corroborate that QS systems regulates heterotrophic nitrification-aerobic denitrification process and some correlating enzymes activities,illuminating this phenomenon is not exceptive to P.aeruginosa.In further,when different carbon sources were supplied to the medium,we found that the activity regularity is the same as described above and the addition of citrate as the sole carbon resource can increase the nitrogen removal efficiency.When used different nitrogen resources in medium,we observed that nitrite couldn't be completely utilized when PQS is over produced or overproduced,indicating only proper content of PQS can promote nitrate removal process.In general,our data showed that AHL and PQS control both nitrification and denitrification process aerobically,suggesting their role in regulating nitrogen removal process where oxygen is existent.Addition of fillers allows bacteria to form biofilms,and the secretion of QS signal molecules can increase the biomass on the fillers.In specific,the biofilm adhesion rates of AHL and PQS-deficient strains lasIrhlI and pqsA were 38.01%and 45.15%,respectively,which were significantly lower than wild strains(45.77%),while the pqsL with excessive secretion of PQS increased to 47.24%compared with wild strains.The composition of EPS was quantitatively analyzed by means of infrared spectroscopy and three-dimensional fluorescence.It was found that the presence of signal molecules promoted the production of hydrophobic proteins,polysaccharides,extracellular DNA and lipids in Pseudomonas aeruginosa,while lacking signal molecules will considerably inhibit this phenomenon.Unlike the growth of suspended bacteria,when forming a stable biofilm,the QS system signal molecules will slightly promote the consumption of ammonia nitrogen in the HNAD process,while the lack of signal molecules will reduce the effect of nitrogen removal.Although the quorum-induced defective strains the lasIrhlI and pqsA have higher denitrification ability than the pqsL.This result was attributed to the fact that signal molecules will promote the formation of biofilm and a large amount of EPS,which masks the adverse effects of signal molecules on the HNAD process of suspended bacteria and even promotes the degradation of ammonia nitrogen.