Figure 4.

Environmental fluctuations affect the diversity and function of microbial communities. (A)The regularity of nutrient fluctuations is essential to produce regular oscillations in the microbial communities of mice (Thaiss et al. 2014; Zarrinpar et al. 2014) and humans (Thaiss et al. 2016). (B) Fluctuations in a privileged nutrient source enhance the long-term maintenance of a newly introduced bacterial strain into a pre-existing murine gut microbiota (Kearney et al. 2018). The introduced strain could be detected after 60 days without the privileged nutrient if introduced within 35 days of nutrient fluctuations (top), whereas the strain could not be detected when introduced with 35-days of steady nutrient exposure (bottom). (C) Environmental fluctuations can induce lasting changes in community composition, even after the environment returns to pre-fluctuation conditions. This bistability (blue) in microbial behavior is observable as a different post-perturbation steady state (ii) than the initial steady state (i). Recent studies have observed such bistability after a single pulse (left, steady gray) (Tropini et al. 2018) or series of environmental fluctuations (right, fluctuating gray) (Kearney et al. 2018; Nguyen et al. 2020).