Effects Of AHLs-quorum Sensing On The Anammox System Under Aerobic/anaerobic Conditions

Oxygen molecules emerged much later than ancient anaerobic microbes,allowing them to develop various defense mechanisms(such as superoxide dismutase SOD and peroxidase CCP)against the toxic effects.Anammox process(anaerobic ammonia oxidation)has great potential in wastewater treatment,but it is easily poisoned by oxygen.Previous studies have focused on the detoxification mechanism of anammox system,but little attention is taken on the role of quorum sensing(QS)based on AHLs(Acyl-homoserine lactones).Therefore,this study operated the UASB reactor of anammox sludge for 612 days,including oxygen stress(400 days)and oxygen detoxification process(212 days).Then we added BRPC3-HSL inhibitor to anammox sludge to explore the change of nitrogen removal.The role of AHL based quorum sensing in oxygen stress and oxygen detoxification was also focused.The main results are as follows:1.During oxygen stress,the DO of 3-4mg/L greatly affected the nitrogen removal;the removal of ammonia and nitrite capped at 57.6±15.6%and 62.1%±15.6%,respectively.The anammox sludge granules also underwent obvious disaggregation.2.The dominant species of Candidatus Kuenenia in the sludge decreased from 15.3%on the 7th day to 7.4%on the 164th day,and reached the highest of 20.7%on the317th day,then decreased to the lowest of 6.0%on day 377.Compared with day 7,the abundance of SOD1 gene encoding superoxide dismutase increased by 3.0%at day317,and the abundance of CCP gene encoding cytochrome c peroxidase increased by4.8%at day 317,indicating that the bacteria secreted more SOD and CCP.It is speculated that these genes play an role in assisting anammox bacteria to resist the stress of oxygen.3.In the process of oxygen detoxification,the microorganisms in the reactor showed a good recovery,and the removal of ammonia and nitrite recovered beyond 90.0%within 92 days.Anammox sludge was vulnerable to short oxygen exposure(about 2hours),and the removal of ammonia and nitrite decreased rapidly to 34.5%and 47.1%.The process was reversible,requiring 17 days to recover.When the influent NLR(Nitrogen influent loading rate)increases from 0.3 to 0.45 kg-N/m~3/d,anammox sludge shows good resilience to loading shock.The removal of ammonia and nitrite could reach 93.7%and 92.0%in 32 days.4.During oxygen stress and detoxification,p value of sod1 between aerobic and anaerobic phase is less than 0.001,showing a significant change and importance in the fight against oxygen.Quorum sensing worked in two phases,characterized by AHLs signal molecule contents and genetic changes.Las R was correlated with multiple nitrogen metabolism genes.C6-HSL,C8-HSL and C10-HSL showed significant negative correlations with Las I-lux I and Tra R,while C6-HSL was positively correlated with Las R and negatively correlated with C8-HSL and C10-HSL.5.The addition of Br PC3-HSL inhibitors(Las R and Tra R inhibitor)for 20h did not affect the species of anammox sludge,but phenotypes and genes of community function did.sod2,sod1 and ccp,tpx,gpx,kat G,and other superoxide dismutase genes jointly promote the oxygen consumption of anammox bacteria,and promote the transformation from an aerobic phenotype to an anaerobic phenotype.The addition of methanol and inhibitors reduces the conversion of the facultatively anaerobic to an anaerobic phenotype.However,the inhibitors had no obvious effect on sod1 and ccp while the inhibitors may have less inhibitory effect on tpx and gpx.6.Br PC3-HSL Inhibitors have significant inhibitory effects on the secretion of AHLs signaling molecules,las R and tra R.The inhibitory effect on tra R is much stronger than that on las R,while dct S、dct R、fix L、fix J、rhl R of other Lux R families are not affected by the inhibitors.In the process of nitrogen metabolism,quorum sensing inhibitors inhibit nir S、nos Z、nir D、nos R and other genes,thus interfering with the denitrification process of nitrite conversion to nitric oxide and nitric oxide conversion,and reducing the degradation level and efficiency of ammonia nitrogen and nitrite nitrogen.During the oxygen stress and detoxification process,microbial community structure and the succession of functional genes of anammox bacteria were investigated,and the role of QS in signal transduction and activation of microbial functions was explored.However,further metagenomic and metabolomic analyses are suggested to elucidate the key enzyme functions at the transcriptional level,as well as the effects of the quorum sensing system on the nitrogen cycle enzyme genes,superoxide dismutase genes,and cytochrome c peroxidase genes.