Screening of methomyl-degrading bacteria from river

• Main Authors: Tzu-Wei Wu, 吳姿緯
• Other Authors: Chien-Jung Tien
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/06754759076839347191

碩士 === 國立高雄師範大學 === 生物科技系 === 99 === River biofilm is a microbial community attaching on biotic and abiotic substrates. It has special contribution to river self-purification. Many studies have found that river biofilms were able to degrade organic pollutants. Methomyl is a carbamate pesticide, and one of the commonly used pesticides. Thus, contamination of methomyl in the aquatic environment may cause toxic effects on environmental organisms and adverse effects on ecosystems. This study would like to investigate the ability of bacteria in natural river biofilms to degrade methomyl and screen bacteria with degradation potential for methomyl. Natural river biofilms were colonized on ceramic discs for 21 days in Tsen-Wen River. Screening culturing was performed for 28 days after collecting natural river biofilms. The degradation test was run for 7 days after screening culturing. Concentrations of methomyl were measured using high performance liquid chromatography (HPLC). The results showed that river biofilms on ceramic discs after screening culturing could remove 90.6% of added methomyl in 7 days. After 28-day screening culturing, river biofilms on ceramic discs were removed and attached on loofa sponges (bacterial mixtures A). The bacterial mixtures A could remove 92.16% of added methomyl. After 28-day screening culturing and 7-day degradation test, river biofilms on ceramic discs were removed and attached om loofa sponges (bacterial mixtures B). The bacterial mixtures B could removed 92.4% of added methomyl. The results suggested that long time screening culturing could increase capacity of bacterial mixtures to remove methomyl. The bacterial mixtures A and B were preserved at 25℃, 4℃ and -20℃ for one and three months. The highest capacity of bacterial mixtures A to remove methomyl was preserved at -20℃ for 3 months among those preserved at different conditions, but lower than that of non-preserved bacterial mixtures A. For bacterial mixtures B, the highest capacity to remove methomyl was preserved at -20℃ for one month, but lower than that of non-preserved bacterial mixtures B. Bacterial diversity did not correlated with their ability to remove methomyl. The results indicated that bacterial mixtures preserved at different conditions would cause in a decrease in their methomyl-removal capacity. Three bacterial species were isolated from river biofilms. Only one species identified as Sphingomonas sp. showed ability to remove methomyl with removal rate of 32.51%. Denaturing gradient gel electrophoresis results showed that bacterial diversity decrease with an increase in screening culturing time for river biofilms. The survival bacterial species after screening culturing may be tolerant to methomyl and have potential for degrading methomyl. The experimental data fitted well with zero order model. Bacterial mixtures on ceramic discs showed the highest capacity to remove methomyl and had degradation half-life of 3.2 days. Concentration of methomyl in river water was estimated as 194 μg/L according to Fugacity model. If river water was contaminated with 194 μg/L of methomyl, it could be removed by bacterial mixtures on ceramic discs, bacterial mixtures A, bacterial mixtures B, and Sphingomonas sp. within 0.8, 1.2, 1.8 or 2.3 hours, respectively.