A novel high-throughput drip-flow system to grow autotrophic biofilms of contrasting diversities

The impact of community diversity on the functioning and assembly of microbial systems remains a central questions in microbial ecology. This question is often addressed by either combining a few cultures without necessarily a history of coexistence, or by using environmental communities, which are often ill controlled and thus likely to be poorly reproducible. The purpose of this work is to develop a high-throughput continuous-flow system for growing replicate microbial biofilms of varying, but controlled, average thickness and associated community diversity. With these replicate biofilms, the effect of community composition and diversity on various ecological processes can then be rigorously examined. We hypothesize that the increased loading, resulting in thicker biofilms, will decrease the drift in the community and impose limited environmental filtering by providing more diverse niches. Thus, thicker biofilms are likely to host greater diversity. A system with 40 replicates has been constructed using flow-through polypropylene columns housing a defined number of single-sized glass beads supported by a stainless steel mesh. Biofilms consisting primarily of ammonia oxidizing and nitrite oxidizing bacteria are cultivated on the beads using a drip-flow assembly by feeding a mineral medium containing ammonium-N as sole energy source. Biofilm thickness is controlled by setting the surficial loading rate to 0.168 g NH4- N/m2/day or 1.678 g NH4-N /m2/day, which should theoretically result in biofilms with average thickness of 100 or 1000 μm. We will present the differences observed in community composition between systems run at high and low loading rates for 60 days. We will also evaluate community activity by measuring nitrification efficiency and correlate that to microbial diversity. In conclusion, we hope to demonstrate a high-replicate biofilm cultivation systems that allow us, by altering the loading rate, to engineer biofilms towards prescribed differences in composition, opening new opportunities to explore community assembly processes and their link to ecosystem function.