Research On Degradation Of Chlorpyrifos And Stress Adaption In Rice By Multi-Functional Microbiota

Chlorpyrifos is a broad-spectrum chlorinated organophosphorus pesticide,which is widely used to control pests in rice,wheat and other crops because of its high efficiency and low cost.However,its long-term large-scale application leads to excessive chlorpyrifos residues in many agricultural products,endangering human health.Endophytes are microorganisms whose whole life activities are in the intercellular spaces,tissues and organs of the host plants;they have stable living space in the host plants and have complex microecological relations with plants.With the isolation and purification of endophytes,using functional endophytes to promote pesticide degradation in plants is a novel strategy to control pesticide residues in agricultural food products.In this study,several endophytic bacteria were isolated and screened from the root tissues of rice plants under chlorpyrifos stress,and the chlorpyrifos degradation ability and growth performance of each strain were explored.Two complex flora with different functions were constructed,which colonized rice to analyze their effects on chlorpyrifos degradation and stress adaptaion in rice plants.The main research findings are as follows:1.One hundred and forty-two(142)strains were isolated and screened from root tissues of rice under chlorpyrifos stress by morphological observation combined with 16 S r RNA analysis.The strains belonged to Bacillus sp.,Pseudomonas sp.,Enterobacter sp.,Aeromonas sp.,Hydrophilic sp.,Bacteria sp.,Aureobacter sp.,Acidophilus sp.,Acinetobacter sp.,Foggerella sp.,Bacillus sp.,Pseudomonas sp.,Flavobacterium sp.and Alkylophilus sp.,among which Bacillus sp.was dominant,followed by Pseudomonas sp.2.The chlorpyrifos degradation and growth-promoting function of the strains were studied.A total of 41 chlorpyrifos-degrading bacteria were identified in vitro degradation experiments.When the initial concentration of chlorpyrifos was 1 mg/L,the degradation rate reached 31.37%～88.64%,and the strain CP4 had the strongest degradation ability for chlorpyrifos.The results showed that 36 strains could promote growth,among which 17,9,15,10 and 13 strains had the functions of IAA production,iron carrier production,phosphorus solubilization,nitrogen fixation and potassium solubilization,respectively.Strain CP6 had the strongest comprehensive function of promoting growth,including the above five functions of promoting growth,and its IAA yield was 107.64 mg/L.Among them,23 strains have both degradation and growth promotion functions.3.In order to construct the complex flora with degradation or growth-promoting function,the degrading bacteria CP4(Pseudomonas sp.),CP43(Bacillus sp.)and the growth-promoting bacteria CP2(Bacillus sp.),CP6(Pseudomonas sp.)were selected as representative strains to construct the flora.By drawing the growth curve,it was found that the strains reached the stationary phase after being cultured for about 8 hours.In addition,the interactions between CP4,CP43,CP2,and CP6 were found to promote each other,but there was no antagonism.Degradation bacteria and growth-promoting bacteria were mixed in a ratio of 1:1,respectively,and degradation bacteria(CP4+CP43)and growth-promoting bacteria(CP2+CP6)were obtained.4.Pot experiment was conducted to study the effects of different microbial groups on physiological indexes and chlorpyrifos residues in rice.Through antibiotic screening and plate recovery tests,it was found that each strain could successfully colonize rice.Under chlorpyrifos stress,five physiological indexes including plant height and root length of uninoculated and inoculated rice were measured.Compared with uninoculated rice,the plant height,root length,fresh weight and chlorophyll content of rice inoculated with growth-promoting bacteria(CP2+CP6)increased by 17.27%,51.31%,36.04% and 22.71%respectively,and the electrolyte permeability decreased by 26.41%.The fresh weight of rice plants were significantly increased by 23.84% after inoculation with degrading bacteria(CP4+CP43).Chlorpyrifos residues in rice plants with different treatments were also determined.The results showed that chlorpyrifos residues in rice plants without inoculation were 7.78 mg/kg.After inoculation,chlorpyrifos residues in rice plants with degrading flora and growth-promoting flora decreased significantly to 3.34 mg/kg and 4.12mg/kg,respectively.The results showed that inoculation of growth-promoting bacteria and degrading bacteria could alleviate the stress of chlorpyrifos in rice plants.