Quantitative Autecological Study of Microorganisms in Soil by Immunofluorescence

The Immunofluorescence Approach in Microbial Ecology

“…The growth curve was conventional and closely similar to that obtained by plate count, with a mean generation time of 14 hr by either procedure. Growth features of the same strain inoculated into nonsterile soil and followed by FA were strikingly different (Schmidt, 1974). Growth rates were extremely slow, with a mean doubling time of 240 hr in one of the test soils and 365 hr in another.…”

“…All of the work cited, together with the development of suitable procedures to permit the enumeration of bacteria in natural habitats by FA (Bohlool and Schmidt, 1973a;Schmidt, 1974), was either preliminary in the sense of assessing the FA technique for ability to detect rhizobia in the complex soil environment, or developmental as was necessary to overcome the limitations that were encountered. None of the ecological questions that have been difficult or impossible to approach by indirect methods had yet been addressed by FA.…”

“…The validity of this approach is questionable on both practical and theoretical grounds. In practice, cell densities must be unusually high in order to detect a specific microorganism in a soil dilution (Schmidt, 1974). MPN statistical estimates are based on dilution to extinction so that some of the inocula for replicate tubes have one bacterium per unit volume.…”

“…Development of procedures to enumerate specific bacteria in soil (Bohlool and Schmidt, 1973a;Schmidt, 1974) was particularly pertinent to the autecology of the nitrifiers as a possible alternative to the MPN method. Schmidt (1974) inoculated a partially sterilized soil with a strain of N. winogradskyi originally isolated from that same soil, added nitrite as substrate, and followed Nitrobacter growth by FA along with nitrate formation.…”

“…A method devised for quantitative FA examination of soil bacteria was first outlined by Bohlool and Schmidt (1973a) and later presented in more detail by Schmidt (1974). Essential steps in the method involve dispersion of a diluted soil sample to release bacteria into suspension, flocculation to remove soil particulates from the supernatant fluid, filtration of a portion of the supernatant fluid through an appropriately pretreated membrane filter, and finally then microscopic enumeration of the specific bacterium on the FA-stained membrane filter surface.…”