Morphogenesis of Phototrophic Biofilms is Controlled by Hydraulic Constraints and Enabled by Architectural Plasticity

Biofilms are structured microbial communities with a spatial configuration that influences their emergent properties and ecological success. Using flume experiments and automated optical coherence tomography, we studied the morphogenesis of phototrophic biofilms along a gradient of hydraulic conditions characteristic for small streams. A compact and coalescent biofilm formed under fast flow, whereas protruding clusters separated by troughs formed under slow flow. While the experimentally imposed hydraulic conditions drove this remarkable morphological differentiation, amplicon sequencing did not reveal significant differences in biofilm community composition. Biofilm morphogenesis was linked to flow-induced displacement and reciprocal interactions between biofilm structure and local hydraulics. Automated profiling with microsensors in combination with optical coherence tomography mapped oxygen mass transfer within and around biofilm structures, providing evidence for the local alteration of the mass transfer regime. Overall, these findings evidence the strong coupling between architectural plasticity, efficient mass transfer and mechanical resistance to shear in a phototrophic biofilm.