Characterization Of Highly Effective Atrazine-degrading Bacteria And Enzymes

As the extensive use of atrazine in the world, it has become one of the worst contamination pollutants of soil and water, microbial degradation of atrazine is of particular interest because of the high mammalian toxicity of such compounds and their widespread. In this thesis, the analytical method, degrading-bacteria enrichment, isolation and characterization of a high efficiency atrazine-degrading Strain BZB-1 were studied systematically. The main results were as follows:Four isolates of atrazine-degrading bacteria were isolated from the sludge around the wastewater outlets of atrazine-produced factories in Shandong and Hebei Provinces. All of the isolates were differentiated by observing clearing zones on indicator agar plate containing 1000 mg/L atrazine, and utilized atrazine as the sole source of nitrogen. But four isolates varied in abilities to degrading this pesticide. Among them, one isolate, BZB-1 was selected for further analysis for its high degrading efficiency. This isolate was identified as Shinella granuli by 16s rDNA sequence analysis and morphological, physiological and biochemical characters. The isolate Cells are Gram-negertive, non-spore-forming, motile rods, Amorphous or finger-like flocculent growth occurs in liquid media. Catalase- and oxidase-positive, and it is novel genus and strain.The isolate grows well in much wider temperature and pH ranges in beef peptone medium, with 30℃and 7 as the optimum. The ability of the isolate to mineralize atrazine was investigated under different culture condition. The results suggested that atrazine concentration, inoculating quantity, culture pH and period had great effects on the degradation efficiency of atrazine, except temperature. The rate of degradation varied between 45.6% and 100% according to different influencing factors. Investigation of the trend of degradation showed that the higher degrading rate (89.5 %) within first 3 days, and reached a percentage of 100% of degradation within 7 days (6.59×10~9cfu/ml , atrazine 1000mg/L, liquid mineral medium 50ml, 30℃, shaking with 180 r/min).The degrading-enzyme produced by Shinella granuli BZB-1 are located inside of its cell, and they are structured-enzyme. Temperature and pH are key factors affecting enzymes degrading activity. The enzymes showed the highest activity at 35℃with the degrading rate 73.5% (protein content: 1.04mg/ml, reaction time:30min) in atrazine-degrading experiment. The degrading-enzymes had wider comfortable pH range than degrading-bacteria BZB-1. As pH varies among 5-9.2, the composite enzymes showed varied degrading activity, and degrading activity increased in line with pH with the highest degrading rate 69.6% at 9.2 (protein content: 0.93mg/ml, reaction time:30min) .Generally, the present results highlight the isolate of this bacterium and its degrading-enzyme to be used in the contamination control of pesticide pollution in agricultural environment.