Enrichment of oligotrophic bacteria at microsites of soil.

Abstract

Responses of oligotrophic bacteria at microsites of soil to substrates at various concentrations were studied by means of capillary tubes. As a measure of dominance of oligotrophic bacteria, an index .delta. was proposed as follows: .delta. = (DNBcount-NBcount)/DNBcount where NB and DNB count are plate count on the conventional nutrient broth (NB) and its 100-fold dilution (DNB). The value of the index varied widely with the site and was most frequently observed at 0-0.1 or 0.9-1.0, which is interpreted by an assumption that a population developed in a capillary tube consists of offspring of one or few of the original cells. The assumption is consistent with the J-shaped cell density histogram which is approximated by the Poisson distribution. Bacterial response to substrate is expressed by the mean .delta. value, 3 types of responses being observed; glucose and succinate were effective for the enrichment of oligotrophic bacteria, glutamate for zymogenic ones and nutrient broth affected favorably either the former or the latter depending on its concentration. A probabilistic view is proposed on bacterial behavior at microsites of soil.