Fig. 4

Morphological adaptation to limiting substrate conditions in the chemostats (a) and in retentostat (b). In the chemostats, at low-growth rates cells were smaller rods in comparison with high growth rates. In the retentostat, a transition from rod (0 d) to coccus shape was observed after 42 days at near-zero growth condition. This morphological change increases the surface-to-volume ratio of the cells maximizing the interface for transport of substrates and nutrients. Data points show the average from the evaluation of two biological replicates of chemostats and one replicate in the case of the retentostat (R1 in Fig. 2)