Isolation and characterization of DNB
A total of 64 isolates were obtained from the8 samples processed. Out of these isolates. 108 were found positive for nitrate reduction and only 14 were positive for borth nitrate and nitrite reduction. These ภ isolates were subjected to physiological and molecular characterization. All the 14 isolates were characterized for denitrification properties under oxic and anoxic conditions and screened for the presence of nirS, nirK and nosZ genes using PCR. Though all the isolates were positive for borth nitrate and nitrite reduction, only 11 were positive for gas productions . While other isolates produced gas under both oxic and anoxic conditions, CDN14 was found to produce gas only under anoxic conditions. In CDN-8,10.11 and 14. No gas was observed inter initial experiments under anoxic conditions, however inoculating the tubes with double the size of the inoculums resulted in gas production. In isolates CDN3-8, 10 and 11, nitrate and nitrate and nitrite reduction wes comparatively more rapid under oxic conditions than anoxic conditions except CDN14 that was found efficient only under anoxic conditions. In nitrate broth, CDN14 exhibited siow growth under oxic conditions with negligible nitrite production only inside the Durham tube indicating preference for oxygen-limited conditions.