Determination of the Number of Respiring Thiobacillus ferrooxidans Cells in Water Samples by Using Combined Fluorescent Antibody-2-(p-Iodophenyl)-3-(p-Nitrophenyl)-5-Phenyltetrazolium Chloride Staining.

Fluorescent antibody staining was combined with 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride reduction in a procedure termed FAINT to allow for the direct microscopic determination of specific actively respiring populations of bacteria in a variety of aquatic habitats. The FAINT procedure is simple, precise, and appropriate for use in a wide variety of autecological studies. The distribution of Thiobacillus ferrooxidans was examined by FAINT enumerations in both acidic and nonacidic sites. Comparisons among the FAINT technique and fluorescent antibody staining alone or most-probable-number determinations in 9K broth showed that the use of most-probable-number determinations resulted in an underestimation of the number of viable cells by one to three orders of magnitude, whereas fluorescent antibody counts resulted in an overestimation of the number of viable T. ferrooxidans. The amount of difference was not consistent but varied, depending on the sample site.