Competition for nitrate between denitrifying Pseudomonas stutzeri and nitrate ammonifying enterobacteria

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.