Stabilizing microbial communities by looped mass transfer

Creating structurally and functionally stable microbial communities would be of great benefit to biotechnology but so far has proven challenging. Here we propose a looped mass transfer design that keeps communities constant for long periods of time. The effluent of five parallel reactors, which started with the same inoculum, was mixed in a reactor representing a regional pool. Part of this pool was, after mixing, transferred back to the five reactors. Community dynamics were monitored and visualized by quantitative microbial flow cytometry and selected taxonomic sequencing of whole communities and sorted subcommunities. The rescue effect known from metacommunity theory was the main stabilizing mechanism and led to the survival of subcommunities with zero net growth, especially at high mass transfer rates. The looped mass transfer approach promises to overcome the notorious stochastic structural fluctuations in bioreactors and has the potential to design and stabilize communities performing desired functions.