Length of incubation for enumerating nitrifying bacteria present in various environments

The effect of incubation time on most-probable-number estimates of autotrophic nitrifying bacteria was investigated by using waters, rooted aquatic plants, sediments, and slimes as inoculum sources. Maximum most probable numbers of the NH4+-oxidizing group were attained in 20 to 55 days (median, 25). Estimates of NO2-oxidizers were highest at termination (103 to 113) days.