Fig. 6.

Interaction type distributions from hybrid oxic–anoxic simulations for two organism pairs. a E. coli with B. subtilis. b E. coli with S. enterica. Both hybrid simulations demonstrate that regardless of organism, availability of oxygen is a strong determiner of the potential for bidirectional exchange. When oxygen is not provided to an organism in these simulations, it tends to provide metabolites to its partner, resulting in an abundance of commensal interactions. These scenarios may act as a “stepping stone” toward fully anoxic environments, in which mutualistic interactions become more prevalent