Shifts and rebound in microbial community function following repeated introduction of a novel species

Natural microbial communities continually encounter novel species that may successfully establish or simply be transient, yet both outcomes can alter the resident community composition and function. Preserving natural microbial communities and innovating synthetic ones requires insight on the immediate and long-term impact of species introductions on both composition and function. For instance, it remains unclear whether there are gradual and long-term impacts from repeated introductions where the introduced species fails to establish – so-called failed invaders. To investigate the persistent impacts by failed invaders, we present an experimental test of community stability over multiple generations against repeated novel species introduction. We propagated a natural microbial community from a traditional fermented milk beverage for approximately 100 generations, with or without, repeated introduction of Escherichia coli at each transfer. Community function was determined by metabolic profiling, and we observed alterations therein immediately after E. coli introduction, followed by recovery, or rebound once ceased. In contrast to this proxy of community function, changes in the bacterial community composition were never detected. Our results evidence that community composition and function do not necessarily respond in parallel to an introduced species, potentially due to genotypic changes below species level detection or metabolic plasticity. Our work shows an ability for functional recovery in microbial communities and contributes insight on long-term community stability to sustained disturbances.