Competition for nitrate between denitrifying<i>Pseudomonas stutzeri</i>and nitrate ammonifying enterobacteria

Abstract

Competition for nitrate between nitrate ammonifying enterobacteria and a denitrifying pseudomonad was studied in electron acceptor-limited chenostats. In pure cultures, using different carbon and energy sources, the C/N-ratio needed for denitrification is far lower than that required for nitrate ammonification. In mixed cultures of Citrobacter freundii and Pseudomonas stutzeri, competing for nitrate with l-lactate as electron donor, the nitrate ammonifying organism dominated at dilution rates of D ≤ 0.14 h−1. Competition for both nitrate and l-lactate at a dilution rate of D = 0.05 h−1 always resulted in the coexistence of both species. Using glucose as additional carbon source, the final ratio of nitrate ammonifying and denitrifying organism depended on the C/N-ratio as well as on the dilution rate. The results of the study are discussed with respect to field data.