Central taxa are keystone microbes during early succession

Microorganisms underpin numerous ecosystem processes and support biodiversity globally. Yet, we understand surprisingly little about what structures environmental microbiomes, including how to efficiently identify key players within these complex, hyper-diverse communities. For decades microbiome network theory has predicted that highly-connected "hub" taxa act as keystone microbes that have disproportionate effects on their communities. However, this has not been empirically tested in nature. Combining culturing, sequencing, and microbial networks, we isolated "central" (highly-connected, hub taxa), "intermediate"(moderately-connected), and "peripheral" (weakly/unconnected) microbes and experimentally evaluated their effects on soil microbiome assembly during early-stage succession in nature. When central microbes were early colonizers, they significantly (1) enhanced biodiversity (30-40% richer communities), (2) shaped trajectories of microbiome assembly, and (3) increased recruitment of additional influential microbes by greater than 60%. This work elucidates fundamental principles of network theory in microbial ecology and demonstrates for the first time in nature that central microbes act as keystone taxa.