Study of the nitrite degradation mechanism of Shewanella sp.

• Main Authors: Wei - Ru Tsai, 蔡維如
• Other Authors: Ying - Tang Huang
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/50866165765781603138

碩士 === 國立高雄海洋科技大學 === 海洋生物技術研究所 === 103 === Aquaculture in Taiwan is intensive; this causes the concentration of nitrogenous wastes to quickly increase. Probiotics can improve the environment and help living host bacteria; however, probiotics that degrade nitrous acid currently on the market not provide benefits. Our laboratory has previously isolated a bacterial strain from the intestinal tract of whiteleg shrimp (Litopenaeus Vannamei) capable of degrading nitrous acid. After 16S rRNA sequencing, this strain was determined to be Shewanella sp. (MB-1). The doubling time for MB-1 is 36.9 minutes; it can survive in temperatures 28°C-37°C, effectively degrade nitrite in 1-8% salinity and pH 6-9, and is not hemolytic. However, MB-1 cultivated in an LB without NaCl cannot degrade nitrite. Ten ionic compounds were used to cultivate MB-1 and it was found that those cultivated in eight of these ionic compounds could degrade nitrous acid. MB-1 cultivated in KCl and NaCl were able to degrade nitrite one hour faster than that cultivated in MgCl2. In addition, after redissolving MB-1 in PBS or NaCl solutions to culture 48 hours in sea water, it was found that only MB-1 redissolved in PBS could degrade nitrite, increasing cellular nitrite and inducing nrfA expression. While cellular nitrite could be increased and nrfA expression induced in recovery experiment, its ability to degrade nitrous acid was unable to be reestablished. These results suggest that high concentrations of chloride ions prevent nitrite from entering the cells and suppress nrfA expression and the activity of nitrous acid degradation systems. The specific mechanisms require further investigation. As MB-1 is not hemolytic, it can be used in future field studies to assess its application in aquaculture.