Dynamics of a Free-Living Nitrogen-Fixing Bacteria Population Lacking of Competitive Advantage Towards an Antagonistic Population

The dynamics of a model of a free-living nitrogen-fixing population, grown in a chemostat alone or in competition with a non-nitrogen-fixing population, was studied through bifurcation analysis. It is demonstrated that the ability of the nitrogen-fixing population to survive depends on the ammonia and carbon source concentrations and the kinetics parameters of the system. Under competitive conditions the nitrogen-fixing population, characterized by low growth rates, can survive alone at stable steady state only at low dilution rate values. Especially, there is a threshold of the dilution rate above which only the competitive population can survive. When amensalistic interactions are established, coexistence of both populations is favored. At low dilution rate values the survival of the nitrogen-fixing population alone is restricted while this population can survive at higher ammonia concentrations either in coexistence state or in multistability state together with the competitive population. When nitrogen-fixing population successfully inhibits its competitor, then its survival is enhanced towards the coexistence state.