Ecological study of twoNitrobacter serotypes coexisting in the same soil.

The problem of competition betweenNitrobacter strains was posed by the fact that two serotypes (N.w and L) coexisted in a soil, as shown by immunofluorescence. The L serotype had a lower growth rate in pure culture than serotype N.w, as well as a slower nitrifying activity when inoculated to a sterilized soil percolated with NO2 (-) solution. When both serotypes were inoculated together, only N.w was observed by immunofluorescence at the end of the percolation; when in the control soil the two serotypes were identified, strain L always adhered to particles. Maintenance of the two serotypes in the soil could be explained as their exploitation of distinct ecological niches. Thus the relative in situ importance of the two strains is governed by environmental conditions.