Immunofluorescence studies of Nitrobacter populations in soils

Certain steps of a protocol to enumerate a bacterium directly in soil by immunofluorescence were studied with respect to the enumeration of Nitrobacter in soils of diverse properties. Maximal counts of Nitrobacter were obtained by varying factors involved in the release of bacteria from the soil. Differences with respect to these factors were related to soil-colloidal properties. Enumeration protocols modified with regard to soil properties were used with strain-specific fluorescent antibodies (FA) to enumerate Nitrobacter populations (a) in soil during storage, (b) in comparison with most probable number (MPN) enumeration, and (c) occurring in a spectrum of soil samples. FA counting was rapid and precise and gave counts generally 10- to 100-fold higher than obtained by MPN. Nitrobacter cells of the two serotypes studied, designated as agilis and Winogradsky, occurred in each soil at levels of 10(4)-10(5) per gram.