Mechanism Of E.Coli Invasion Into Soil And Its Interaction With Native Community

The large-scale livestock and poultry production in the world can produce a large number of animal wastes,which can cause serious illness outbreak in human and other animals when the wastes are used directly as organic fertilizer to the farmland system without any effective sterilization.Escherichia coli O157:H7(E.coli O157:H7),a common pathogenic microorganism spread between human and animals,is dangerous due to its low infective dose(as few as 10 cells)and high pathogenicity.Besides,E.coli O157:H7 has the potential to be transported into water,vegetables and animals and represents a serious risk to public health and safety.As an important part of soil system,soil microorganisms including microbial abundance,diversity and functions present some feedbacks when soil system exposed to invasion.Hence,understanding the interaction between E.coli O157:H7 and native community will be helpful in exploring the microbial pollution processes and reducing the likelihood of soil microbial contamination.In the present study,the effects of different soil types and carbon additions upon the E.coli O157:H7 persistence in the soil,the legacy effects of E.coli O157:H7 invasion will leave in the soil native community,functional responses of soil native community after E.coli O157:H7 invasion and specific indigenous species interacted synergistically or suppressively with E.coli O157:H7 selection are explored.Main results are as follows:(1)Among the abiotic and biotic soil characteristics,p H value,microbial diversity and resource availability are key driving factors during the E.coli O157:H7 invasion.A longer E.coli O157:H7 survival time was observed in higher soil p H(4.30±0.55 to 7.23±0.12);microbial diversity is positively related to E.coli O157:H7 survival time in soil as well as resource availability.Furthermore,toxin genes carried by E.coli O157:H7 can also leave a significant effect on its survival time which wild strain carried all toxin genes survived shortest and non-toxin strain longest in soil.Carbon addition changed the interaction between invader strain and native community,and ultimately increased the invasion success probability.(2)E.coli O157:H7 left legacy effects upon soil native microbial structure,composition,carbon source utilization and community niche estimated by high-throughput sequencing and Biolog techniques.The community niches of soil native community increased and metabolic potential also changed after E.coli O157:H7 invasion.In addition,non-toxic strain invasion left bigger effects on the soil native community than wild strain carrying all toxic genes.Data analysis showed that there was significantly positive correlation between E.coli O157:H7 survival time and Bray-curtis distance of soil community,which proved that invasion impacts on native community depended on the invasion time.(3)The survival time of E.coli O157:H7 in soil and interaction with native community were explored by setting gamma-irradiated soil and non-irradiated soil treatments.Results showed that:(i)the E.coli O157:H7 survival time was considerably related to the competition for resource and niche between invader and native species;(ii)E.coli O157:H7 invasion significantly promoted the soil organic carbon mineralization;(iii)carbon resources addition increased soil respiration significantly and accelerated the irradiated community recover process.In a word,soil microbes play important roles in the resistance of exotic invader,especially in the resource competition perspective.(4)This research selected 40 strains from soil community to explore the possible specific interaction with E.coli O157:H7.The result showed M.foliorum exerted an emergent synergistic effect on E.coli O157:H7 survial in the addition of D.cellobiose.It was found that these two strains can't utilize D.celloboise alone,but co-culture system showed a significant growth of strains.Furthermore,the emergent synergistic effect between E.coli O157:H7 and M.foliorum was not universal.In addition,M.foliorum can enhance the biofilm growth of E.coli O157:H7 regardless oligotrophic and eutrophic conditions.Most important,M.foliorum can prolong the survival time of E.coli O157:H7 in soil which can enlarge the invasion effect.