Impact On Prometryne Degradation In Soil Through The Interactions Between Nematodes And Microbes

More and more herbicides and other pesticides are being used in modern agriculture. The application of herbicides contaminated soil, air and water, affecting the exsistence of organisms in environment, and the health and safety of human beings severely. Therefore, remediation of pesticides contamination is of critical significance. Microbes have been used to remediate the contamination of pesticides because they are numerous, tiny, reproductive and rich in diversity. Bacterial-feeding nematodes are one of the most important bacterial-grazers in soil. Interactions between bacterial-feeding nematodes and microbes together with their ecological effects in terrestrial ecosystems have aroused great attention of ecologists due to nematodes’ abundance and close interactions with microbes. Many researchers found bacterial-feeding nematodes could affect the number, activity and community of microbes due to the release of nutrients and their grazing preference on different microbes. Up to now, the experiment results were not consistent. Some researchers found out that bacterial-feeding nematodes could decrease the number of microbes and weaken the nitrogen and phosphorus mineralization. However, the general trend is that bacterial-feeding nematodes in most cases enhance nitrogen and phosphorus mineralization and increase the number of microbes. The impacts vary with the species and density of nematodes and bacteria, as well as the surrounding environmental conditions, such as the humidity and temperature. Therefore, the microbial activities could be affected directly or indirectly by bacterial-feeding nematodes, and it is believed that the degradation of pesticides could be affected by the interactions between bacterial-feeding nematodes and microbes.On the basis of previous experiments in our lab and other research, some further experiments have been processed and carried out. First, two prometryne-degrading bacteria were isolated, screened and identified from the sediments in a pesticide factory. Second, an anti-prometryne nematode was reared by adding appropriate prometryne into media where bacterial-feeding nematode will grow. Third, gnotobiotic microcosm experiments were conducted to study the interactions between anti-prometryne nematode and bacteria together with their effects on the degradation of prometryne in soil, and the number and activity of prometryne-degrading bacteria by inoculating with anti-prometryne nematode and prometryne-degrading bacteria strain P-1 or P-2. Then, experiments with natural soil (soil was not sterilized but directly inoculated with anti-prometryne nematode) were done to further study the interactions between anti-prometryne nematode and native microbes in soil together with their effects on the degradation of prometryne in natural soil, and the activity and community structure of microbes.The main results were as follows:1. Two prometryne-degrading bacteria were screened and isolated from a pesticide factory, named as P-1 and P-2, respectively. These 2 strains were identified as Ochrobactrum sp. (G") and Bacillus sp. (G+) based on the physiological and biochemical characteristics and homology analysis of their 16S rDNA sequences.46.46% and 65.41% of prometryne (40 mg/L) could be degraded within 12 days by strain P-1 and strain P-2.2. An anti-prometryne nematode was reared in our lab through inoculating the nematode extracted from the contaminated soil into basic salt media containing bacteria and prometryne (the concentration of prometryne was gradually increased from 10 mg/L up to 80 mg/L during the rearing time). The anti-prometryne nematode was identified as Cephalobus Bastian, it can grow in different media with different concentrations of prometryne, but its growth will be affected by different media and different concentrations of prometryne. The anti-prometryne nematode did not grow in BPA media, but it could grow better in MSM media than in PSA media. The growth of anti-prometryne nematode was decreased by the concentration of prometryne in the order of 20 mg/L,5 mg/L and 40 mg/L.3. Strain P-1 and strain P-2 could degrade prometryne in soil, but the rate of prometryne degradation is less than that in liquid media. The degradation of prometryne could be increased by the consortium of strain P-1 and strain P-2. The number of prometryne-degrading bacteria, strain P-1 and P-2 and soil respiration and soil enzyme activity were increased during the experiment by inoculating anti-prometryne nematode into gnotobiotic microcosm, and FDA hydrolysis activity was boosted more obviously than catalase activity by inoculating anti-prometryne nematode.4. Microbial biomass C and microbial biomass N, soil respiration and soil enzyme activity were enhanced by the use of prometryne in the beginning of the experiment, but were weakened in the later stage. Inoculating anti-prometryne nematode also could boost microbial biomass C and microbial biomass N, soil respiration and soil enzyme activity in natural soil. The degradation of prometryne was strengthened after anti-prometryne nematode was inoculated into soil, which enhanced soil enzyme activity. The results of DGGE showed that the diversity of microbes in soil were affected by the interactions between prometryne and anti-prometryne nematode during the experiment, the diversity of soil microbes was increased during O～8th day, and decreased during 8th～18th day, then increased during 18th～30th day.To summarize, the research probes into the interactions between anti-prometryne nematode and microbes and their effects on the degradation of prometryne in soil, some theories of the interactions between bacterial-feeding nematode and microbes have been made clearer. This research has provided some new information and methods on remediation of contaminated soil, and to some extent enriches the theories and future application in bioremediation.