The enhanced mineralization of organic @entity1568 by bacteriophagous protozoa is thought to favor the nitrification process in soils, in which nitrifying bacteria have to compete with heterotrophic bacteria for the available @entity3104 . To obtain more insight into this process, the influence of grazing by the bacteriovorous flagellate Adriamonas peritocrescens on the competition for limiting amounts of @entity3104 between the @entity3104 -oxidizing species @entity31614 and the heterotrophic species Arthrobacter globiformis was studied in the presence of Nitrobacter winogradskyi in continuous cultures at dilution rates of 0.004 and 0.01 h. The @entity3104 concentration in the reservoir was maintained at 2 mM, whereas the @entity413 concentration was increased stepwise from 0 to 7 mM. A. globiformis won the competition for limiting amounts of @entity3104 when the @entity413 concentration in the reservoirs increased, in agreement with previously described experiments in which the flagellates were not included. The numbers of nitrifying bacteria decreased as the numbers of heterotrophic bacteria rose with increasing @entity413 concentrations. Critical C/N ratios, i.e., ratios between @entity413 and @entity3104 in the reservoirs at which no @entity1507 was found in the culture vessels, of 12.5 and 10.5 were determined at dilution rates of 0.004 and 0.01 h, respectively. Below these critical values, coexistence of the competing species was found. The numbers of nitrifying bacteria decreased more in the presence of flagellates than in their absence, presumably by selective predation on the nitrifying bacteria, either in the liquid culture or on the glass wall of the culture vessels. Despite this, the rate of @entity1507 production did not decrease more in the presence of flagellates than in their absence. This demonstrates that no correlation has to be expected between numbers of nitrifying bacteria and their activity and that a constant nitrification rate per cell cannot be assumed for nitrifying bacteria. Above the critical C/N ratios, low numbers of nitrifying bacteria were still found in the culture vessels, probably because of attachment of the nitrifying bacteria to the glass wall of the culture vessels. Like the numbers of heterotrophic bacteria, the numbers of flagellates increased when the @entity413 concentrations in the reservoirs increased. Numbers of 2 x 10 and 12 x 10 flagellates ml were found at 7 mM @entity413 at dilution rates of 0.004 and 0.01 h, respectively. It was concluded that the critical C/N ratios were practically unaffected by the presence of protozoa. Although @entity1507 production rates were equal in the presence and absence of flagellates, the numbers of nitrifying bacteria decreased more strongly in their presence. This indicates a higher activity per nitrifying cell in the presence of flagellates.

Effects of Grazing by Flagellates on Competition for XXXX between Nitrifying and Heterotrophic Bacteria in Chemostats.

@entity1568 :: ('MESH:D009584', 'Chemical') :: ['nitrogen'] @entity31614 :: ('915', 'Species') :: ['Nitrosomonas europaea'] @entity1507 :: ('CHEBI:48107', 'Chemical') :: ['nitrate'] @entity3104 :: ('MESH:D000644', 'Chemical') :: ['ammonium'] @entity413 :: ('MESH:D005947', 'Chemical') :: ['glucose']
@entity3104 :: (MESH:D000644,Chemical) :: ['Ammonium']
