Theoretical models for the control of bacterial growth rate, abundance, diversity and carbon demand

Abstract

Our conceptual understanding of the role of heterotrophic bacteria in pelaglc ecosystems and in ocean biogeochemical cycles is closely linked to our understanding of how their growth rate, abundance, and diversity is controlled.Here we discuss consequences of the simplifying assumption that there are only 5 potentially important interactions between heterotrophic bacteria and their biological and chemical environment.We consider 3 possible types of growth rate limitation: (1) organic carbon, (2) inorganic phosphate, and (3) organic and inorganic nitrogen; and 2 types of cell losses: (1) predation by heterotrophic flagellates, or (2) lysis by infectious viruses.Incorporating this into sirnple food web structures, we discuss 4 classes of models, 2 based on carbon limitation and 2 based on mineral nutrient limitation of bacterial growth rate.Bacterial abundance is assumed to be controlled by protozoan predation in all cases.For each class, we derive expressions describing bacterial carbon demand, and dscuss the control of bacterial carbon demand, growth rate and diversity.It is shown how models predicting an ecosystem production of dissolved organic carbon (DOC) exceeding bacterial carbon demand may be constructed assuming either a low degradability of the DOC, or mineral nutrient h i t a t i o n of bacterial growth rate.For 2 classes of models, infectious viruses are shown to affect neither growth rate nor abundance of the steady state bacterial community.For all 4 classes of models, viruses are suggested to control diversity of the steady state bacterial community.