Characteristics And Mechanism Of Pseudomonas Stutzeri N2Degradation Of Phenolic Pollutants

Because of its source variety in environment, the phenolic compound is a kind ofwidely existing environmental pollutant. It is toxic, thus, it brings great harm to theenvironment. The treatment of microorganisms is an important way to clean up thispollutant from the environment. It has been reported many strains can degrade phenol,however, the phenol degradation, particularly its ring-opening cracking, is ratherdifficult. In line with the preliminary study, our group had isolated and screened a strainPseudomonas stutzeri N2. This research optimizes conditions, under which bacteria N2can degrade phenol by the ring-opening fragmentation pathway, so as to promote thedecomposition and complete mineralization of toxic phenolic compounds.Based on the previous studies, this thesis probes the degrading potential ofPseudomonas stutzeri N2to phenol pollutants under conditions of using phenol as thesole carbon source, phenol and cometabolism as the carbon source, and nitrophenol asthe carbon source, etc. The results are as follows:（1） When the Pseudomonas stutzeri N2grew on phenol as a sole carbon source, thePseudomonas stutzeri N2could bear1000mg/L phenol. When the initial concentrationsof phenol were within50mg/L⁸00mg/L, there was no toxicity to the Pseudomonasstutzeri N2which growth rapidly. And the net Growth△OD550nm of40h can reach1.27. The synchronous degradation rate of phenol was100%. But its main degradationpathways with phenol as a sole carbon of the Pseudomonas stutzeri N2were thehydroxylation and methylation pathways, which were not beneficial for phenolmineralization and would generate the typical carboxylated product:p-Hydroxybenzoate and the subsequent methylated products. And this failed to detectthe ring-opening cleavage product. （2） Ethanol, as the most effective co-metabolic carbon source, could promotePseudomonas stutzeri N2to degrade phenol by ring-opening cracking way, and couldproduce large amounts of2-hydroxy muconic semialdehyde （HMS）, which is favorableto phenol mineralization.（3） When Ethanol was the co-metabolic carbon source, Ca²⁺would inhibit thering-cracking degradation of phenol. But ammonium chloride, as the most effectivenitrogen source, could prompt Pseudomonas Stutzeri N2to produce more ring-openingproducts. At the same time, the conditions of pH8-9, large amount of vaccination（>10%）, as well as the24.3mmol/L Fe²⁺was very beneficial for the PseudomonasStutzeri N2’s degradation of phenol under open-loop splitting ways, producing moreHMS. When Ethanol was the co-metabolic carbon source, two kinds of metabolicmodes, the Hydroxylation-ring opening cracking pathway and carboxyl-methylationco-existed, with the ring-opening cracking way as the major one. In total, eightsubstances were identified, three of which also presented in the reaction solution of thephenol as the sole carbon source. They were p-hydroxybenzoic acid and the subsequentmethylated products. Another five kinds of products existing only in degradationprocess when ethanol as co-metabolic carbon source were pyrocatechol, hydroquinone,adipate, hydroxy muconic semialdehyde2, hydroxy-mucic acid2.（4） The Pseudomonas stutzeri N2could decompose p-nitrophenol which hasgreater toxicity than phenol. The Pseudomonas stutzeri N2can bear200mg/Lp-nitrophenol. With the increase of the p-nitrophenol concentration, its toxicityincreases gradually. When the initial concentration was50mg/L, it would not generatetoxicity to the Pseudomonas stutzeri N2, which grew rapidly after vaccinated. Thegrowth△OD550nm of36h could reach0.64. The synchronous degradation rate ofp-nitrophenol was24.3%. What’s more, the Pseudomonas stutzeri N2was cultivatedunder vitamin B6, ammonium nitrate as the nitrogen source, alkaline conditions whichcould help to improve the microbial degradability of p-nitrophenol. When the pH is9,the decomposition efficiency of phenol was27.6%in24hours. The Pseudomonasstutzeri N2degradation of p-nitrophenol is through reverting to an amino compoundfrom nitro compound and then being further hydroxylated and methylated. Thus, themain transformative products were nitro-amino products, nitro amino methylated products and nitro aminated hydroxylated products.The thesis research result laid an foundation for applying Pseudomonas stutzeri N2to the ecological restoration of the phenolic pollutants.