No abstract

17Complex microbial biofilms orchestrating mainstream anaerobic ammonium oxidation 18 (anammox) represent one of the most promising energy-efficient mechanisms of fixed 19 nitrogen elimination from anthropogenic waste waters. However, little is known about 20 the ecological processes that are driving microbial community assembly leading to 21 functional anammox biofilms in engineered ecosystems. Here, we use fluorescence in 22 situ hybridization and 16S rRNA sequencing combined with network modelling to elu-23 cidate the contribution of stochastic and deterministic processes during anammox bio-24 film development from first colonization to maturation in a carrier-based anammox re-25 actor. We find that distinct stages of biofilm development emerge naturally in terms of 26 structure and community composition. These stages are characterized by dynamic suc-27 cession and an interplay of stochastic and deterministic processes. The staged process 28 of biofilm establishment appears to be the prerequisite for the anticipated growth of 29 anammox bacteria and for reaching a biofilm community structure with the desired 30 metabolic capacities. We discuss the relevance of this improved understanding of 31 anammox community ecology and biofilm development concerning its practical appli-32 cation in the start-up and configuration of anammox biofilm reactors. 33 34 35In order to understand the ecological processes that lead to anticipated AMX growth in 85 biofilms, we investigated the microbial community assembly on synthetic biofilm car-86 riers from a pilot scale mainstream anammox reactor, over the course of a year from 87 first colonization to mature biofilms. We hypothesized i) that heterotrophic bacteria are 88 the pioneering colonizers that initiate biofilm formation and create the required base 89 layer for second wave colonizers including AMX, and ii) that structure and succession 90 of biofilms can be divided into three distinct growth stages -colonization, succession 91 and maturation. We expected colonization to be driven by initial colonizers capable to 92 attach and grow on the industrial carrier surface. Succession was expected to be driven 93 by increasingly intense competition for space and nutrients in the juvenile biofilm. The 94 mature phase represents the convergence to a well-adapted quasi-equilibrium state de-95 termined by the environmental factors in the reactor. We further assumed that both sto-96 chastic (e.g., birth, growth, death and immigration) and deterministic processes (e.g., 97 environmental factors, biotic interactions, niche differentiation, historical (e.g., prior-98 ity) effects) are important in varying degrees for community assembly across the dif-99 ferent stages. In accordance with hypothesis ii we therefore further hypothesized iii) 100 that stochastic and deterministic processes are changing in their relative contribution 101 on the community assembly over the different stages of biofilm development. 102By combining fluorescence in situ hybridization and 16S rRNA sequencing of ...