Microbial community and abiotic effects on aquatic bacterial communities in north temperate lakes.

The aquatic bacterial community (BC) plays a vital role in determining the nature and rate of ecosystem function. However, the biotic and abiotic factors influencing BC structure and function are largely unknown. Hence, the current study characterizes the impact of biotic and abiotic factors on aquatic bacterial biodiversity to determine whether the dominant effects are biotic or abiotic by partitioning their relative effects across temperate Canadian lakes. We collected water samples from sixty southern Ontario lakes and characterized their BC and microbial eukaryotic community (MEC) compositions using high throughput metabarcode sequencing of 16S and 18S rRNA gene fragments. The diversity and richness of aquatic BCs differed considerably among our study lakes, and those differences were explained by environmental, spatial, and biotic (MEC) factors (31%, 23%, and 23% of variance explained, respectively). The relatively large contribution from biotic and abiotic factors (54%), relative to spatial effects, shows deterministic processes prevail in shaping BC assembly in freshwater lakes. However, spatial effects also contributed significantly, highlighting the role of stochastic processes (ecological drift and coupled with limited dispersal) in shaping BC structure. Furthermore, our co-occurrence network analysis showed strong positive and negative interactions within and between the BCs and MECs, indicating mutualistic or antagonistic co-occurrence patterns relationships play important roles in driving the variation in BC composition among our sampled lakes. Considered together, our community analyses show that deterministic and stochastic processes combined contribute to determining the aquatic BC composition, and hence likely function as well, across a broad array of temperate freshwater lakes.