Metabolism Of Nitrogen-containing Heterocyclic Compounds By Quinoline-degrading Bacteria Comamonas And Mix Bacterial Consortia

As a kind of typical environmental pollutants,nitrogen-containing heterocyclic compounds are widely present in coking wastewater.Among them,quinoline and indole are two typical representatives.Biodegradation has received extensive attention for pollutants removal because of its eco-friendly and cost-effective.Researchers have conducted many investigations on biodegradation of quinoline,but the bacterial resources are still limited.Therefore,this dissertation was to isolate quinoline-degrading bacteria,investigate the quinoline biodegradation characteristics,and unveil the mechanism of quinoline degradation based on genome annotation.Subsequently,the selected quinoline-degrading bacteria?Comamonas sp.strains Z1 and Z3?were mixed with the indole-degrading bacteria?Acinetobacter sp.strain JW?,which was previously obtained in the laboratory,and the mixed bacterial consortia were used for the co-removal of quinoline and indole.Thus,the degradation performance and influencing factors were determined.Comamonas sp.Z3 exhibited a well capacity for quinoline degradation,which could completely degraded 50²00 mg/L quinoline within 14³6 h.Under the condition of pH 7.0and quinoline concentration of 100 mg/L,quinoline mineralization rate could reach 75%in 24 h.Metal ions like Mn²⁺,Ni²⁺,Cu²⁺,Co²⁺and Hg²⁺could greatly inhibit bacterial growth and quinoline degradation.When nitrate was used as external nitrogen source,it promoted the growth and biodegradation of strain Z3 in the first 8 h.In addition to using quinoline as the carbon source,various compounds such as benzoate,salicylate and catechol could also be used for growth.Both Comamonas sp.Z1 and Z3 could degrade quinoline with the production of soluble colored pigments,but the color was obviously different.Intermediates of 2-hydroxyquinoline,2,8-dihydroxyquinoline,8-hydroxycoumarin and 2,3-dihydroxyphenylpropionic acids were detected by high performance liquid chromatography-mass spectrometry product?HPLC-MS?.Thus,the biodegradation of quinoline by Comamonas sp.strains possibly proceeded via8-hydroxycoumarin pathway.Genome sequencing analysis revealed many functional genes related to the degradation of aromatic compounds in strains Z1 and Z3,and the key genes responsible for quinoline degradation were also identified,such as qor,mhp and bph genes.Furthermore,quinoline 2-oxidoreductase?Qor?from strains Z1 and Z3 displayed47.74⁶1.17%similarities with the known one,which catalyzed the first step of quinoline degradation,and the maximal specific activity of Qor in cell-free extracts of strains Z1 and Z3was 0.264 and 0.062 U/mg protein,respectively.When quinoline degrading bacteria and indole degrading bacteria are mixed,the removal of quinoline and indole was quite efficient.When strains concentration OD₆₆₀=0.8¹.0,Z1/JW=1/6,and the pH range was 6.5⁸.0,the bacterial consortia could remove 100 mg/L quinoline and 25¹50 mg/L indole within 36 h.When the bacterial species concentration OD₆₆₀=0.8¹.0,Z3/JW=1/7,and the pH range was 7.0⁸.5,the bacterial consortia could reduce 50mg/L quinoline and 25¹50 mg/L of indole within 36 h.Addition of phenol could promote the growth of mixed bacterial consortia.