Enterobacter Strain 9410-o with Porous Substrates to Enhance Heterotrophic Activity in Bottom Water Environment

Mesophilic Enterobacter strain 9410-O isolated from a eutrophic bottom water environment and introduced into it to enhance heterotrophic activities and decompose organic matters in situ. The bacteria were added as cell suspension after absorbing with porous substrates, like Eco-breath, Neo-coal and Accela35. The strain stimulated net regeneration of dissolved inorganic nitrogen and inorganic phosphorus from the sediment by approximately three to fourfolds at 21 and 23 ̊ C, respectively. It appears that the application of Enterobacter strain 9410-O with Neo-coal as substrate would be promising for the purification of eutrophic bottom water environment. Introduction Uranouchi Inlet, Kochi prefecture, Japan is highly eutrophic due to anonymous practices of fish cage culture with high protein nutrient input, mainly in the form of high protein content in fish feed. A small portion of total fish feed input is recovered by the cultivated fish but a large portion remain either dissolved into the recipient water or settle down onto the sediment (Hans and Enell 1990, Kupka-Hansen et al. 1991, Hall et al. 1992 and Johnsen et al. 1993). Furthermore, inlet is characterized by limited water exchange and pronounced density stratification in summer with oxygen-rich surface and oxygen-deficient bottom environment. These imply heterotrophic activities at the study site are limited by dissolved oxygen (DO) concentration in summer, especially in bottom environment. For improving organic rich bottom environments by stimulating heterotrophic activities, it was envisaged that addition of some promising bacteria possessing higher metabolic activities in a specific limiting environmental situation might accelerate the decomposition rate in situ. The objectives of the present work were, (i) selection of effective indigenous mesophilic bacterial strain, (ii) selection of an useful substrate to carry bacterial cells into the sedimentbottom water complex system, and (iii) enhancement of heterotrophic activity in the system. Materials and Methods Study site and sampling: Mitsumatsu sampling and study station in Japan is a eutrophic area of the Uranouchi Inlet practicing intensive fish farming in cages (Fukami et al. 1991b, Karim et al. 2003). The average depth near the sampling point was 17-18 meter. Water samples were collected from bottom (16 m depth) environment and sediment samples were collected from 0 1 cm deep surface sediment. Isolation and selection of bacteria: One hundred and ten bacterial strains were isolated from the sediment of the study site in October, 2000. Considering growth pattern and colony morphology 20 bacterial strains were primarily selected for further study. Corresponding author. Laboratory of Microbiology, Department of Botany, University of Dhaka, Dhaka1000, Bangladesh. .