THE OCCURRENCE OF OBLIGATORILY OLIGOTROPHIC BACTERIA IN THE SOIL

In incubation experiments attemption were made to obtain approximate data about the numbers of obligatorily oligotrophic bacterial in the soil. For this purpose the soil was treated with various substrates at concentrations selectively toxic to oligotrophs and then decreases in the numbers of living cells in the soil bacteria community were determined using the microscope or the culture method. Distinct decreases in numbers were found only by means of the microscope method as the culture method revealed only a small number of obligatory oligotrophs in the soil. In the presence of each of the applied substrates, i.e. casein hydrolysate, glycine, nicotinic acid, thiamine or NaCl the decreases in the number of living bacterial cells occurred already after several hours and they were accompanied by accumulation of dead cells. The observed toxic effect reached its maximum after 2 days, this level, irrespective of soil type, corresponded to at least one half of the total number of bacterial cells found in the control soil. The extent of this effect was rather indicative of the predominance of obligatory oligotrophs in soil bacteria community. The elimination of obligatory oligotrophs from this community due to the applied substrates did not decrease the amount of CO2 evoluted from the soil.