Abstract
Some heterotrophic bacteria in surface seawater (SSW), living on natural organic compounds such as sugars and lipids, can decompose artificial chemical substances. The enriched nature of deep seawater (DSW) may facilitate the activities of these bacteria. In the present study, degradation of one, ten and one hundred mg l-1 of phenol was compared in vitro among the four media, SSW, DSW, mixture of SSW and DSW (1: 1) and distilled freshwater. The DSW and SSW were pumped from depths of 440 and 0 m, respectively, in the Pacific Ocean off Owase, Mie Prefecture. Tested concentrations of phenol were degraded in SSW and DSW (but not in distilled freshwater) as follows: 1 mg l-1 of phenol was almost completely degraded in SSW, DSW and the mixture in two days; 10 mg l-1 of phenol was almost completely degraded in two days in DSW and the mixture, while degradation rate was less than 60 % in SSW; although 100 mg l-1 of phenol was not perfectly degraded in any seawater after five days, the degraded amounts of phenols increased unlike with lower phenol concentrations. Initial numbers of bacteria in SSW, DSW and the mixture were 89000, 530 and 41000 CFU ml-1, respectively. The number increased most in the mixture, attaining 106 CFU ml-1 during the period. These results suggested that the mixture of SSW (bacteria-rich, nutrientpoor) and DSW (bacteria-poor, nutrient-rich) was optimal and that the in situ release of DSW can be a good tool for enhancing bioremediation to degrade artificial chemical compounds.
