Fig. 1.

Co-cultivation of two facultative mutualists. Cell numbers of X. retroflexus in monocultures and cocultures with P. amylolyticus. a, b The facultative mutualism between the two species after two days. There was a significant increase of X. retroflexus in cocultures compared with monocultures (P < 0.001) and also a significant increase of P. amylolyticus in cocultures compared with monocultures (P < 0.001). c, d The facultative mutualism between the two species was maintained after 8 days of cocultivation in the static environment (X. retroflexus P < 0.001 and P. amylolyticus P < 0.001). Boxplots are Tukey style and P-values are from a linear mixed-effect model. Data are based on 25 biological replicates from three separate experiments (n = 25)