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Abstract Microbes are known to shape topographies; however, mechanisms of biofilm‐sediment interactions and the dynamic evolution of biofilm‐covered bedforms remain poorly understood. Here, we explore the effects of synthetic biofilms on the geometry and temporal evolution of underwater bedforms through flume experiments. Our results demonstrate that synthetic biofilms can produce sedimentary structures similar to those formed by natural microbes, including wrinkles, pits, flip‐overs, roll‐ups, mat chips, and erosional edges. We observed the formation of wrinkles, a common geological feature, due to the accumulation of sand grains on the biofilms. Furthermore, we demonstrated that biofilms can reduce bed roughness by an order of magnitude in the low flow regime. However, the subsequent biofilm‐sediment interactions can increase local bedform size, forming multi‐scale geometries of bedforms. Our study improves the fundamental understanding of the landscape dynamics of bedforms covered by natural biofilms. 

Abstract Biofilms are subjected to many environmental pressures that can influence community structure and physiology. In the oral cavity, and many other environments, biofilms are exposed to forces generated by fluid flow; however, our understanding of how oral biofilms respond to these forces remains limited. In this study, we developed a linear rocker model of fluid flow to study the impact of shear forces onStreptococcus gordoniiand dental plaque‐derived multispecies biofilms. We observed that as shear forces increased,S. gordoniibiofilm biomass decreased. Reduced biomass was largely independent of overall bacterial growth. Transcriptome analysis ofS. gordoniibiofilms exposed to moderate levels of shear stress uncovered numerous genes with differential expression under shear. We also evaluated an ex vivo plaque biofilm exposed to fluid shear forces. LikeS. gordonii, the plaque biofilm displayed decreased biomass as shear forces increased. Examination of plaque community composition revealed decreased diversity and compositional changes in the plaque biofilm exposed to shear. These studies help to elucidate the impact of fluid shear on oral bacteria and may be extended to other bacterial biofilm systems.