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 δ was proposed as follows;
δ=(DNBcount-NBcount)/DNBcount
where NB and DNB count are plate count on the conventional nutrient broth (NB) and its 100-fold dilution (DNB) respectively. The value of the index varied widely with the site and most frequently observed between 0 and 0.1 or 0.9 and 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 δ value, three 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. Baesd on these results a probabilistic view is proposed on bacterial behavior at microsites of soil.
