Isolation,Identification,Degradating Characteristics And Soil Bioremediation Application Of Imazethapyr-degrading Strain QC-13

Imazethapyr is one of the widely used herbicides in China.It has been used for its high efficiency and low cost.Because of its high phytotoxicity and the likelihood of its transportation in surface runoff,the use of imazethapyr ultimately caused more serious environment pollution.An imazethapyr-degrading bacterium,named strain QC₁3 was isolated from imazethapyr-contaminated samples using selective culture medium with imazethapyr as the sole carbon source.The strain was identified based on its morphological,physiological and biochemical tests,with reference to Bergey's Manual of Determinative Bacteriology combined with 16S rRNA gene sequence analysis.Based on these analysis,strain QC-13 was finally identified as Bacillus sp.Strain QC-13 could degrade more than 68.2%of 50 mg/L imazethapyr within 7 d.The optimal temperature and pH for the growth of strain QC-13 was 30? and 7.0,respectively.There was a positive correlation with the growth and aeration.The optimal NaCl concentration was 10 g·L-1.The optimal pH value and temperature for the degradation of imazethapyr were 7.0 and 30?,respectively.The optimal inoculation was 2%?V/V?.The degradation metabolites by strain QC-13 of imazethapyr in the culture medium extracts were isolated and identified by LC/MS.Two metabolites of imazethapyr were detected.Based on the identified products,the degrading pathway of imazethapyr was speculated.The effects of imazethapyr on the culturable bacteria,actinomycetes and fungi were studied with a short-term treatment of this herbicide at different concentrations.The concentration of imazethapyr inhibited the soil bacterial growth at the beginning.However,after two weeks the inhibition effect disappeared.At the same time promoting effect appeared,the higher concentration,and the more obvious promoting effect.Imazethapyr has no significant effect on fungi.Imazethapyr shows strong inhibition effect on actinomyces.The inhibition effect of soil respiration by imazethapyr was found be fugacious.The bioremediation of imazethapyr-contaminated soil by inoculating QC-13 cell was studied under laboratory conditions.After inoculating strain QC-13 into soil,66.2%of imazethapyr at concentration of 10 mg.kg-1 dry soil was degraded at 21d.The soil with inoculation of strain QC-13 could effectively degrade imazethapyr.the non-sterilized soil was better than that in sterilized soil.The opportune soil moisture and neutral or weak alkalescent condition could stimulate strain QC-13 to degrade imazethapyr in soil sample.