A bacterial strain capable of degrading trimethylamine was isolated from an aeration tank of waste water plant by enrichment culture method. The microorganism was aerobic, Gram-negative, and straight rod, with the dimensions 0.5 to 0.6 by 1.5 to 2.0 $\mu{m}$. The bacterium has no flagellum and is non-motile. The strain was catalase-positive and oxidase positive, and G+C content of DNA was 68.5 mol %. The microorganism can not assimilate methane aerobically but can grow with C-1 compounds such as methanol, dimethylamine and methylamine as sole carbon and energy source at aerobic condition. Glucose and maltose could serve as growth substrate too. Based on the morphological, physiological characteristics, the bacterial strain was identified as one of Genus Methylobacterium. In the presence of ammonium chloride, the degradation of trimethylamine was enhanced. The excess ammonium ion was released to media. The strain can start to degrade trimethylamine below the half of saturated dissolved oxygen concentration, but after it grows, the high dissolved oxygen concentration increased the degradation rate.
