Manipulating the physical distance between cells during soil colonization reveals the importance of biotic interactions in microbial community assembly

Microbial communities are of tremendous importance for ecosystem functioning and yet we know little about the ecological processes driving the assembly of these communities in the environment. Here, we experimentally manipulated the physical distance between neighboring cells during soil colonization by three microbial communities exhibiting some variations in membership to determine the role of bacterial interactions in soil community assembly. We show that reducing distances between cells resulted in a loss of bacterial diversity with at least 41% of the dominant OTUs being significantly affected by physical distancing depending on community membership. Our results also indicate that high cell density may favor competitive rather than mutualistic interactions. Our study demonstrates that the competitiveness of bacteria strongly depends on cell density and community membership, therefore highlighting the fundamental role of microbial interactions in the assembly of soil communities.