Isolation, Identification And Nicosulfuron-Degradating Characteristics Of Photosynthetic Bacteria

Nicosulfuron is one of new, more efficient bioactivity sulfonylurea herbicide, using for controlling tanaka annual gramineous broadleaf weeds, part of weed and cyperaceae weed on corn. Due to its low dosage, excellent effect and safety to corn, Nicosulfuron has been widely applied in China. But long-term use of Nicosulfuron, it is not avoid of adverse effection to eco-environment. Nicosulfuron residue in corn, soil and underground and surface water is direct coming from Nicosulfuron using. Furthermore, Nicosulforon residue has phytotoxicity to sensitive crops. and weed resistance was also appeared. So this study aimed to isolate and identify Nicosulfuron resedue degrading bacterial strains from soil samples in corn field, and the degrading characteristics was further evaluated, for estimating the potential application of bioremediation of Nicosulfuron residue by degrading bacterial strain.. Main results and conclusions are as follows:1. More than 10 soil samples were collected from cornfield, which Nicosulfuron was for long-term using. And six bacterial strains (named J5-2, J5-3, JX-2, JX-3, JX-6, J4-8) with using Nicosulfuron as sole carbon source were isolated by enrichment culture. The homology alignment analysis of sequences of pufM (shown in appendix) and 16S rDNA (GeneBank registration number for HM053962, HM163161, HM163162, HM163160, HM053960, HM053961) testified that these strains were belong to Purple nonsulfur bacteria, which was an important cluster of phytosynthetic bacteria.2. The degrading efficiency experiments of isolated bacterial strians were tested, the PSB media (pH7.5) with 2% inocula, cultured in 25℃,2500 Lx illumination, the Nicosulfuron residue was quantified by HPLC (High Performance Liquid Chromotography). Strains of J5-2, J5-3, JX-2, JX-3, JX-6, J4-8 could degraded 400mg·L-1 of Nicosulfuron upto 30.8%.21.4%,19.8%,25.6%.23.7%,20.1% in 7 d. respectively. Strain J5-2 is the heghest one to degrade Nicosulfuron in the same conditions, and selected for futhter degrading experiment.3. Strain J5-2 was identified by morphology, physiological and biochemical characteristics, living cells light absorbance,16S rDNA sequence phylogenetic analysis, and the results showed strain J5-2 is closely as a member of Rhodopseudomonas. Biological characteristics indicated that strains J5-2 can use variety of carbon, nitrogen source and using Nicosulfuron as sole carbon, and the optimal growth conditions were pH 7.0,30℃,6% inocula,2500 Lx illumination.4. The degrading characterristics experiments, such as Nicosulfuron initial concentration, temperature and initial growth medium pH illumination, inocula. and so on were conducted by strain J5-2. The results showed that strain J5-2 could tolerate Nicosulfuron up to 1600 mg·L-1, and the optimal degrading conditions were 30℃, pH 7.0,2500 Lx illumination, respectively. Strain J5-2 could degrading 400 mg·L-1 of Nicosulfuron up to 33.5% in 7 days in optimal degrading conditions. The degrading characteristics also verified strain J5-2 could degrade Pyrazosulfuron, Bensulfuron methyl, Fenpropathrin. Cypermethrin, Bifenthrin, Ethofenprox. Nicosulfuron was easily spontaneous degradation in acidic condition, and stubborn in neutral and alkaline conditions.