The effect of diazinon on soil bacterial communities and its degradation by a mixed bacterial culture isolated from a paddy field
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Diazinon is an organophosphorus insecticide which is used widely in the rice paddies of Iran. It has been shown that continuous and repetitive applications of pesticides in soils alters the microbial community structures towards the enrichment of pesticide-degrading microorganisms which can, in turn, be used for bioremediation of these agrochemicals. In this research, we aimed to assess the impact of diazinon on microbial communities of paddy soils and isolate a degrading mixed bacterial culture. The experimental soils were sampled from a paddy located in the north of Iran (Gilan Province) with a long history of diazinon application. A liquid mineral salt medium (MSM) containing filter-sterilized diazinon as the only source of carbon was used to isolate the pesticide-degrading bacteria from the paddy soil using two enrichment cycles with 50 and 150 µg ml1 of the pesticide. Variations in the soil bacterial communities as a consequence of diazinon application and also the bacterial components of the selected degrading mixed culture were analyzed using denaturing gradient gel electrophoresis (DGGE). The samples which were subjected to DGGE were as follows: (a) soils treated three times with diazinon at 15 µg g−1, (b) soils treated three times with diazinon at 150 µg g−1, (c) control soils without any pesticide treatment incubated under the same conditions as the treated samples, and (d) the isolated mixed bacterial culture. Cluster and principal component analysis (PCA) of the DGGE banding pattern obtained from soil bacterial populations revealed that they were only affected at the 150 µg g−1 of diazinon. This was also supported by a phylogenetic tree obtained from sequences of the main gel bands. Accordingly, bacterial populations belonging to Proteobacteria were enriched in the soil following three treatments with diazinon at 150 µg g−1. The Shannon’s index revealed a non-significant increase (P ≤ 0.05) in the overall diversity of the soil bacteria following diazinon application. The isolated diazinon-degrading mixed bacterial culture in the MSM was able to remove 90% of the pesticide at two concentrations of 50 and 100 µg ml−1 by 16.81 and 19.60 days, respectively. Sequencing the DGGE bands confirmed the role of Betaproteobacteria as the main components of the isolated mixed culture in the degradation of diazinon. Generally, the results of this research provide new insights into the identification of diazinon-degrading bacterial populations in the paddy soils and their potential application in bioremediation of this insecticide.
کلیدواژه ها