Preliminary Studies On Glyphosate -degradation By Bacillus Cereus

Glyphosate is one kind of non-selective herbicide after bud stem, which extensively controls dicotyledonous and poaceae weeds, etc. In recent years, glyphosate has been accepted widely and used in our country, because of its excellent effect on weed controlling and the planting of herbicide-resistant crop. At present, the study foucus on glyphosate-resistant crops in China. Currently, glyphosate–degradation strains can provide microbial resources for the study on genetically modified crops. In our experiment, 120 degrading strains were isolated from soil and waste water through enrichment culturing. CW-1strain with strong glyphosate-degradation in these strains was deep studied and the main results are as follows:1. Using enrichment and inoculating culturing technology, we have got 120 strains of glyphosate-degradation microorganism from the waste water and the soil polluted by glyphosate, including 20 strains of fungi and 100 strains of bacteria. The degradation rates of glyphosate were detected by ultraviolet spectrophotometry and high performance liquid chromatography-post column derivation. The result showed that the degradation rates of WF-11strain, CW-1strain and CW-72 strain were higher, WF-11 strain, CW-1 strain and CW-72 strain had the degradation rates of 52.5%, 60.2 % and 56.3%, respectively.2. CW-1 strain was identified Bacillus cereus by biological, physiological, biochemical characteristics and 16S rDNA sequence analysis. The study on degradation characteristics of CW-1 strain was made clearly. The most appropriate degradation conditions were as follows: glyphosate 1500 mg·L-1, culturing time 5 days, temperature 30℃, pH value 8.0, inoculated with concentration of 4 mL (OD600=1) and the glucose concentratiion 5 g·L-1. Under the above optimum conditions, the CW-1 strain had a highest degrading rate of 65.3 %.The tolerance experiment results showed that CW-1 strain grew strongly with glyphosate 16000~32000 mg·L-1, the growth of CW-1 strain was reached the peak with glyphosate 32000 mg·L-1, and CW-1 strain grew slowly in the culture medium 2 with glyphosate 48000 mg·L-1.3. The drug-resistance experiment showed that CW-1 strain grew in culture medium containing ampicillin penicillin and tetracycline, but did not grow in culture medium containing kanamycin and chloramphenicol respectively. Compared with aroA genes of Bacillus cereus that had been reported, aroA gene of CW-1 strain has mutations of many sites. The small plasmid and aroA genes of CW-1 strain have transformed into Escherichia coli. respectively. The transformation of Escherichia coli. can live in glyphosate 48000 mg·L-1 of minimal medium. The degradation rate was 31.9% and 30.6% in improved enrichment culture medium with glyphosate 1500 mg·L-1 . The results show that the small plasmid and aroA genes of CW-1 strains have maybe related to glyphosate-degradation.