Study On The Characteristics And Quorum Sensing Of 1,4-Dioxane Degradation By Acinetobacter Ba Umannii DD1

As a organic solvent stabilizer,1,4-dioxane was widely applied in cosmetics and manufacture. Its toxicity and potential carcinogenicity to ecological environment and human health risk constantly rasied with an increasing environmental emissions. In this case, an effective 1,4-dioxane processing technology was eagerly need. In this thesis, a new 1,4-dioxane-degrading strain was identified as DD1 which isolated from aerobic sludge of wastewater treatment plant. Phenotypic and biochemical characteristics and the metabolic pathways of the bacterium were studied. The environment factors for N-acyl-homoserine lactones (AHLs) secretion and biofilm formation by DD1 were optimized.The main conclusions were shown as follows:(1) A Gram-negative strain DD1, which could use 1,4-dioxane as the sole carbon and energy source, was isolated from the mixture activated sludge obtained from Qige urban sewage treatment plant. According to the Biolog GNIII detection,30 of 71 carbon substrates were easily utilized while inhibited by 21 antibiotics on DD1 growth. The 16S DNA sequence from strain DD1 (accession numbers in GenBank KF713537) had a similarity of 99% to Acinetobacter baumannii AQ-3 (accession numbers in GenBank JF751054.1), suggesting that it belonged to genus of Acinetobacter baumannii. Cells of A. baumannii DD1 could completely degraded 100 mg/L 1,4-dioxane in 42 h with the cells yield of 0.414 mg-protein (mg-1,4-dioxane)-l, demonstrating that DD1 could bear the highest cell yield and degrading activity in ever described strains. Moreover, DD1 tolerated higher 1,4-dioxane concentration almost up to 1000 mg/L.The optimal incubation conditions of strain DD1 under mineral salt medium were 30 ℃ and pH 7.0. During the degradation process of 1,4-dioxane, the oxidation was initiated by monooxygenase in DD1 The detection on metabolic intermediates by GC and GC/MS, intermediates including 1,4-dioxene, ethylene glycol and oxalic acid were detected.(2) During the biodegradation of 1,4-dioxane, kinds of AHLs were secreted by DD1. It could be found that the amount of 3-oxo-C6-HSL (68 pmol) and Cs-HSL (24 pmol) were much more than others. It was determinated that A. Baumannii DD1 had the Acinetobacter signal molecule secretion gene abaI. And there were two genus extensive homology to the Pseudomonas signal molecule secretion gene lasI and rhlI. The AHLs secretion by DD1 could not promote the degradation of 1,4-dioxane directly, but could induce the ability of biofilm formation. The induction of 3-oxo-C6-HSL and Cs-HSL were better than others.(3) When culture conditions were set at 30℃-32℃, pH 7.0, OD6oo 0.15,100 mg/L 1,4-dioxane and 1% NaCl, the ability of AHLs secretion and biofilm formation of A. Baumannii DD1 were to be the maximum. According to the optimal environmental conditions for AHLs secretion and biofilm formation, a biofilm reactor and a suspended reactor were operated. The biofilm reactor showed a strong resistance to 1,4-dioxane shock loading up to 800 mg/L while the suspended reactor crash.