COMPETITION FOR NITRATE AND GLUCOSE BETWEEN PSEUDOMONAS-FLUORESCENS AND BACILLUS-LICHENIFORMIS UNDER CONTINUOUS OR FLUCTUATING ANOXIC CONDITIONS

The dissimilatory nitrate-reducing bacterial community in the rhizosph ere of aerenchymatous plant species such as Glyceria maxima, consists of oxidative. denitrifying and fermentative nitrate-ammonifying bacter ia. To study the respective ecological niches of both types of nitrate -reducing bacteria, competition for nitrate or glucose between the rep resentative denitrifier Pseudomonas fluorescens and the representative fermentative nitrate-ammonifying Bacillus licheniformis under continu ous or fluctuating anoxic conditions were performed in continuous cult ure. Competition started by mixing the separate, steady-slate mono-cul tures of the two species at different ratios. All the experiments were performed at a dilution rate of 0.05 h(-1). The competition was follo wed by measuring concentrations of nitrogen, glucose and fatty acids a nd by determining the cell numbers of P. fluorescens and B. lichenifor mis. Under continuous anoxic nitrate-limited conditions and under cert ain fluctuating anoxic conditions (8 h 10% and 16 h 0% air saturation) , B. licheniformis was able to maintain itself in the chemostat at a l ow percentage of 4-7%. Under continuous anoxic glucose-limited conditi ons and under specific fluctuating anoxic (16 h 10% and 8 h 0% air sat uration) conditions, B. licheniformis washed out. The outcome of the c ompetition was explained by a higher affinity of P. fluorescens for ni trate arid glucose compared to B. licheniformis. B. licheniformis was able to maintain itself in the chemostat under continuous anoxic nitra te-limited conditions and under certain fluctuating anoxic conditions (8 h 10% and 16 h 0% air saturation) due to the fer;mentation of the r emaining glucose. (C) 1998 Federation of European Microbiological Soci eties. Published by Elsevier Science B.V. All rights reserved.