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. Author manuscript; available in PMC: 2016 Mar 1.
Published in final edited form as: Trends Microbiol. 2014 Dec 9;23(3):134–141. doi: 10.1016/j.tim.2014.11.005

Figure 1.

Figure 1

Metabolic interactions within a two-species community. (A) A single mechanism of metabolic exchange can generate diverse functional relationships in liquid (well-mixed) cultures. Figure adapted from [19] © 2012 by The University of Chicago. Mutualism: density of A in co-culture (AB) is larger than when alone (A), and B in co-culture (BA) is larger than alone (i.e., AB>A & BA>B). Red-scale indicates strength of mutualism (AB + BA − (A + B)). Competition: AB<A & BA< B. A exploits B: AB>A & BA<B. B exploits A: AB<A & BA>B. (B) Streptococcus gordonii (Sg) and Aggregatibacter actinomycetemcomitans (Aa) engage in multiple forms of metabolic interactions. Schematic model of Sg–Aa metabolic exchange under aerobic (left) and anaerobic (right) conditions [63]. Open arrows represent a positive effect, whereas oval arrows represent a negative effect upon the population or metabolite they are pointing toward. Sg and Aa form mutualistic or competitive interactions in liquid culture, dependent on oxygenation. Redrawn from [23].