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.
