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SCHMIDT EDWIN L.
Soil Science: September 1974
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ABSTRACTThe fluorescent antibody (FA) technique makes possible an autecological approach to microbial ecology because it permits specific microorganisms to be seen and identified in their natural habitats. A method is reported which further extends the FA technique to the quantification of specific bacteria in aquatic and terrestrial ecosystems. Procedures were developed for the most difficult FA-quantification problem, that of the microorganism growing in soil. The protocol that was evolved included: release of bacteria from soil in a dispersed suspension; flocculation of soil colloids out of suspension; concentration, on a special membrane filter, of the bacteria remaining in a known volume of suspension; staining with appropriate homologous FA; and enumeration of reactive cells by incident light immunofluorescence microscopy.Data are reported on the quantification of several bacteria in soil. FA-counts of Rhizobium japonicum, strain USDA 110, agreed well with viable plate counts as the population developed in sterilized soil. Growth of the same organism in nonsterile soils could be followed only by FA-counts. Growth rates and population features for nonsterile soils differed greatly from those observed in sterile soil or laboratory cultures. Escherichia coli die-off was studied quantitatively in normal, nonsterile soil by selective plating, and by the FA-membrane filter count. Agreement between the two methods was good, but FA counts were high at certain stages, probably due to the rapid accumulation of recently-dead cells. As a final example Nitrobacter was enumerated by specific FA-membrane filter counts during nitrification in a partially sterilized soil to relate the dynamics of growth to the conversion of nitrite to nitrate.

The fluorescent antibody (FA) technique makes possible an autecological approach to microbial ecology because it permits specific microorganisms to be seen and identified in their natural habitats. A method is reported which further extends the FA technique to the quantification of specific bacteria in aquatic and terrestrial ecosystems. Procedures were developed for the most difficult FA-quantification problem, that of the microorganism growing in soil. The protocol that was evolved included: release of bacteria from soil in a dispersed suspension; flocculation of soil colloids out of suspension; concentration, on a special membrane filter, of the bacteria remaining in a known volume of suspension; staining with appropriate homologous FA; and enumeration of reactive cells by incident light immunofluorescence microscopy.

Data are reported on the quantification of several bacteria in soil. FA-counts of Rhizobium japonicum, strain USDA 110, agreed well with viable plate counts as the population developed in sterilized soil. Growth of the same organism in nonsterile soils could be followed only by FA-counts. Growth rates and population features for nonsterile soils differed greatly from those observed in sterile soil or laboratory cultures. Escherichia coli die-off was studied quantitatively in normal, nonsterile soil by selective plating, and by the FA-membrane filter count. Agreement between the two methods was good, but FA counts were high at certain stages, probably due to the rapid accumulation of recently-dead cells. As a final example Nitrobacter was enumerated by specific FA-membrane filter counts during nitrification in a partially sterilized soil to relate the dynamics of growth to the conversion of nitrite to nitrate.

© Williams & Wilkins 1974. All Rights Reserved.