Microbial Community Coalescence for Microbiome Engineering

Microbiome engineering, and especially plant host-mediated microbiome selection (Mueller and Sachs, 2015), is a recently introduced set of methods by which microbial communities are selected in order to maximize certain fitness- or performance-related host functions, most typically of plants, but also for animals. In essence this is a phenomenological approach, acknowledging the holobiont concept of host-microbe associations (Rosenberg and Zilber-Rosen berg, 2016), implicitly encompassing a complex set of generally not very well-understood eco-evolutionary processes including microbial community shifts, (micro-) evolutionary changes and changes in physiology. Clearly, future research will be aimed at unraveling many of the component processes taking place during microbiome engineering, and therefore it is important to fully capture all processes potentially involved. One aspect that has so far not been considered as an underlying process of importance in microbiome engineering is community coalescence; yet, it is quite clear that community coalescence is an integral part of microbiome engineering approaches. Community coalescence is a recently introduced concept (Rillig et al., 2015) denoting the encounter and interaction of entire microbial communities (i.e., the merging of previously separate networks of microbes), a circumstance that is not fully captured by existing theories such as metacommunity theory. In community coalescence, new biotic networks are formed, and also aspects of the abiotic environment may change due to mixing of the source environments. Community coalescence may naturally be quite frequent, and there are many scenarios for this process to occur in soils (Calderon el al., 2016; Rillig et al., 2016) and other environments, including animal hosts and aquatic systems. Despite this, these coalescent events have consequences for which we currently lack the theory and predictive tools.