title: Biophysical aspects of resource acquisition and competition in algal mixotrophs.
abstract: Mixotrophic organisms combine autotrophic and heterotrophic nutrition and are abundant in both freshwater and marine environments. Recent observations indicate that mixotrophs constitute a large fraction of the biomass, bacterivory, and primary production in oligotrophic environments. While mixotrophy allows greater flexibility in terms of resource acquisition, any advantage must be traded off against an associated increase in metabolic costs, which appear to make mixotrophs uncompetitive relative to obligate autotrophs and heterotrophs. Using an idealized model of cell physiology and community competition, we identify one mechanism by which mixotrophs can effectively outcompete specialists for nutrient elements. At low resource concentrations, when the uptake of nutrients is limited by diffusion toward the cell, the investment in cell membrane transporters can be minimized. In this situation, mixotrophs can acquire limiting elements in both organic and inorganic forms, outcompeting their specialist competitors that can utilize only one of these forms. This advantage can be enough to offset as much as a twofold increase in additional metabolic costs incurred by mixotrophs. This mechanism is particularly relevant for the maintenance of mixotrophic populations and productivity in the highly oligotrophic subtropical oceans.
authors.affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. benw@mit.edu
authors.forename: Ben A
authors.initials: BA
authors.lastname: Ward
authors.forename: Stephanie
authors.initials: S
authors.lastname: Dutkiewicz
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Barton
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Follows
mesh_terms: D052818:Autotrophic Processes; D055592:Biophysical Phenomena; D003198:Computer Simulation; D017753:Ecosystem; D004734:Energy Metabolism; D052836:Heterotrophic Processes; D008954:Models, Biological; D010933:Plankton / Q000502:physiology*; D011157:Population Dynamics