A single community dominates structure and function of a mixture of multiple methanogenic communities

To provide insight into the temporal dynamics of compositional and functional change following community mixing, we measured the methane production and composition of two methanogenic communities derived from industrial Anaerobic Digesters (ADs) grown in isolation or as a mixture in laboratory scale ADs. Both the individual communities and mixes were grown in four replicates. To remove any potentially confounding effects caused by differences in starting density of tested communities, we standardized microbial density based on qPCR-estimated counts of 16S rRNA gene copies. We found that the methane production of the mixed community was initially intermediate between the two individual communities, but after 5 weeks propagation started to produce gas at a rate indistinguishable from the more productive of the individual communities. We examined both the starting point and the endpoint composition of the single and mixed communities by Illumina sequencing 16srDNA amplicon libraries. Consistent with the phenotypic data, the composition of the mixture was much more similar to the better than the worse performing community at the endpoint. This was despite the single endpoint communities changing considerably from their ancestral composition over the 5 weeks