Possible sources of assimilatory and dissimilatory Nitrate reducing bacteria in Jaffna peninsula, Sri Lanka

Abstract

Nitrate contamination in the ground water is a common problem worldwide including Jaffna peninsul4 Sri Lanka. Such contamination of drinking water is regulated by World Health Organization all around the world [11mg/L NO3- -N) due to the health effects of over consumption of nirate. Microbial denitrification is an environmentally sound and economically feasible method for remediation of nitrate contaminated water. The aim of the present study was to isolate nitrate reducing bacteria from different environmental samples such as pond sediments, paddy soil, manures and different wastes in Jaffna district. Spread plate and streak plate methods were used to isolate the strains. Around 90 morphologically different bacterial strains were isolated from environmental samples tested. Initial screening was carried out on BTB (Bromothymol Blue) agar plates with nitrate. Among them 70 strains were selected as nitrate reducers from the BTB agar plates. Among the nitrate reducers 38 strains were selected as dissimilatory nitrate reducers and rest of them had assimilatory nitrate reduction characteristic. Since most of the nitrate reducers are facultative heterotrophs, the highest number of strains were isolated from submerged condition namely paddy water and paddy soil. Therefore, submerged condition of paddy land could be the possible source for isolation of more number of assimilatory and dissimilatory nitrate reducing bacteria.