This research investigated the effect of biofilm thickness on microbial community assembly in nitrifying moving bed biofilm reactors (MBBRs). Using biofilm carriers with controlled maximum thicknesses, the study examined the interplay of stochastic and deterministic processes in community assembly. Results indicate that habitat filtration selects for phylogenetically close community members, enriching Nitrospira spp. Stochastic processes were more prevalent in thicker biofilms (≥200 µm), while thinner (50 µm) biofilms showed stronger selection, potentially due to hydrodynamic forces. Thicker biofilms displayed greater phylogenetic beta-diversity, possibly due to variable selection or drift. The findings highlight the influence of biofilm thickness on assembly processes, providing insights into biofilm ecology and potential strategies for microbial community management.

S Jane Fowler, Elena Torresi, Arnaud Dechesne, Barth F Smets