| The intensification of livestock and poultry production has led to increased animal wastes as by-products, which pose serious environmental problems. The well-known Escherichia coli O157:H7 (E. coli O157:H7) is one of the most abundant pathogen in manure, it is dangerous because of its low infective dose and high pathogenicity. Contaminated vegatable is considered as important vehicle of E. coli O157:H7. Contamination of produces with E. coli most likely occurs during the primary production phase when vegetables are grown in contaminated fields. Hence, understanding the survival mechanism of E. coli O157:H7 in soil and its influence of environmental factors will help to reduce the risk of ecosystem contamination and human infection. In the present study, main results are as follows:(1) The cultivation pattern greatly changed the survival dynamics and time of E. coli O157:H7. It survived longer under the plastic-greenhouse cultivation (21.95 days) than that under the open field condition (17.91days), which was related to the level of organic carbon (OC), pH and the ratio of bacteria PLFAs to fungi PLFAs (B/F). The invading E. coli O157:H7 in soil environment not only can be influenced by the soil indigenous microbial community but also can alter the microbial community to some extent. After the E. coli O157:H7 invaded, the results of phospholipid fatty acids (PLFAs) method showed that the abundance of actinomycetous and fungi PLFAs declined, while the ratio of bacteria PLFAs to fungi PLFAs and the ratio of cy-PLFAs to pre-PLFAs increased. The invading E. coli O157:H7 resulted in a more harsh soil microbial community.(2) Results showed that E. coli O157:H7 survival changed greatly after organic fertilizers application, with shorter td values (survival time needed to reach the detection limit of 100 CFU·g-1) in soils amended with chicken manure and the longest in soils amended with pig manure. Soil pH was the important factor in regulating E. coli O157:H7 survival in the test soils, while its effect changed along the pH range of the test soils. Besides, soil electrical conductivity (EC), free Fe/Al (hydro) oxides and the nutrient condition (the NO3--N and water soluble organic carbon content) were also significant explanatory factors for E. coli O157:H7 survival in the test soils.(3) The addition of organic materials significantly prolonged the survival of E. coli O157:H7 in vegetable soil. Among all kinds of organic materials, E. coli O157:H7 survived longest in soils amended with the pig manure. The invading E. coli O157:H7 increased the diversity and richness of the indigenous community, while inhibited the growth of microbial group related with nutrient and energy cycling. The response of indigenous community changed along with the various kinds of organic addition. The soils amended with pig manure and the mixture of pig manure and biochar shared silmliar microbial change pattern, while soils amended with biochar and without addition were silmliar. Moreover, the effect of invading E. coli O157:H7 on soil microbial community would still exist even there was no culturable E. coli 0157:H7 detected.(4) Biochar amendment contributed to slower decline rate of E. coli O157:H7, which was the result of the increase of soil pH and indigenous microbial community. The biochar type showed greater influence than its amount on E. coli O157:H7 survival in soils. The survival of E. coli O157:H7 negatively correlated with the diversity and richness of the soil microbial community. Proteobacteria, Planctomycetes and Firmicutes positively correlated with E. coli O157:H7 decline rate, while Bacteroidetes and Actinobacteria showed opposite effect. The reponse of soil indigenous community was a dynamic process with incubation time. The soil microbial community changed greatest during the initial incubation period, while the Proteobacteria was mostly influenced with a declining relative abundance. During the late incubation, the microbial changes were relatively slow. |
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