Isolation And Screening Of Quinoline And 2-hydroxyquinoline Degrading Bacteria And Their Interaction Relationship

Quinoline is a typical nitrogen-containing heterocyclic organic pollutant,which is widely found in industrial wastewater such as coking wastewater,petrochemical wastewater,and pharmaceutical wastewater.It has teratogenic,carcinogenic,and mutagenic effects and high toxicity,so it needs to be removed.Biodegradation has received much attention and has been widely researched as a kind of economical,efficient,and environmentally friendly treatment method.At present,a variety of different quinoline efficient degrading flora or bacteria have been domesticated and isolated,and screened,but the mineralization efficiency was not satisfactory.Researchers have found that the accumulation of its intermediate metabolite 2-hydroxyquinoline may be the efficiency-limiting step that hinders its complete mineralization.In addition,the interaction relationship and cooperation mechanism between microorganisms in the quinoline biodegradation process is unclear.Therefore,in this study,quinoline and its biodegradation intermediate product 2-hydroxyquinoline were used as carbon and nitrogen sources to domesticate and enrich the degrading flora,from which efficient quinoline-degrading bacteria and 2-hydroxyquinoline degrading bacteria were isolated and screened,and the effect of different combinations of bacteria in degrading quinoline was investigated,and the best combination of degrading bacteria was determined to be Gordonia sp.P6 and Ralstonia sp.Q6.Finally,through metabolite,the metabolites were analyzed,the degradation pathways were inferred and the whole genome sequencing technology was used to reveal the cooperation mechanism in the process of quinoline degradation by the best combination of bacteria.When Gordonia sp.P6 degraded quinoline alone,the removal efficiency of quinoline at 300 mg/L was 69.44% and the mineralization efficiency was57.70% in 120 h.When Gordonia sp.P6 combined with Ralstonia sp.Q6 to degrade quinoline,the removal and mineralization effect of quinoline was enhanced,and the removal efficiency increased to 76.47% and the mineralization efficiency increased to 72.98%.The mineralization efficiency increased to 72.98%,and the combined degradation also accelerated the efficiency of the mineralization process of quinoline.A significant amount of2-hydroxyquinoline production was detected after 24 h of combined bacteria incubation and was rapidly converted by 60 h,which was 12 h faster than the conversion of Gordonia sp.P6 alone.The GC-MS results of the degradation products of the best combination of bacteria showed that the quinoline degradation pathway of strain Gordonia sp.P6 was the 8-hydroxycoumarin pathway;the intermediates from different pathways were detected in the degradation of 2-hydroxyquinoline by strain Ralstonia sp.Q6,so there were at least two different metabolic pathways in its degradation,probably the 8-hydroxycoumarin pathway and the5,6-dihydroxy-2(1H)-quinolone pathway.Gordonia sp.P6 has combined with strain Ralstonia sp.Q6 for the degradation of quinoline by at least two different metabolic pathways,probably the 8-hydroxycoumarin pathway and the 5,6-dihydroxy-2(1H)quinolone pathway,respectively.Whole genome sequencing of the optimal combination of Gordonia sp.P6 and Ralstonia sp.Q6 revealed the mechanism of cooperation at the genetic level.The results showed that Gordonia sp.P6 has several key functional genes,such as nic X,mhp B,pca C,and dsz C,and abundant monooxygenase-encoding genes,but Gordonia sp.P6 alone degrades quinoline with only one degradation pathway and cannot play its functional role.While Ralstonia sp.Q6 is a bacterium with multiple genes that tole-efficiency Q6 is a protein-encoding gene with multiple unfavorable environment tolerance and has more qor genes in its genome,which accelerates mineralization efficiency of quinoline and reduces the toxicity in the culture system to make the bacterium easier to survive.In addition,it possesses an abundance of aromatic compound degradation genes such as the cat A gene and denitrification gene,etc.Ralstonia sp.Q6 has at least two quinoline degradation pathways,thus enabling the key genes within Gordonia sp.P6 to function,accelerating the metabolic transformation of intermediates and reducing the inhibitory and hindering effects.This study reveals for the first time the mechanism of microbial interactions during quinoline mineralization and provides a theoretical basis for the study of bioremediation of quinoline and other nitrogen-containing heterocyclic compounds pollution.