Biomass addition alters community assembly in ultrafiltration membrane biofilms

Abstract

Freshwater biofilms assemble from a pool of rare water column genotypes. Random density fluctuations and temporal species turnover of functionally equivalent potential colonizers result in compositional variability of newly formed biofilm communities. We hypothesized that stronger environmental filtering as induced by enhanced substrate levels might reduce the impact of a locally variable pool of colonizers and instead select for more universal habitat specialists. Our model were heterotrophic biofilms that form on membranes during gravity-driven ultrafiltration of lake water. In four separate experiments, biomass of the cyanobacterium Microcystis was added to the feed water of one set of treatments (BM) and the resulting biofilm communities were compared to unamended controls (CTRL). Biomass addition led to a significant shift of community assembly processes: Replicate BM biofilms were more similar to each other than by chance in 3 of 4 experiments, whereas the opposite was the case for CTRL communities. Moreover, BM communities were more stochastically assembled across experiments from a common ‘regional’ pool of biofilm colonizers, whereas the composition of CTRL communities was mainly determined by experiment-specific ‘local’ genotypes. Interestingly, community assembly processes were also related to both, physiology (aerobic vs. anaerobic lifestyle) and the phylogenetic affiliation of biofilm bacteria.

Micro-Landscape Dependent Changes in Arbuscular Mycorrhizal Fungal Community Structure

“…There have only been a few studies so far quantitatively (i.e., assessing effect sizes on the degree of predictability, rather than simply obtaining a qualitative result such as whether the community is segregated) assessing how predictable synthetic microbial systems can be. A recent meta-analysis on the topic examining 21 datasets showed that organic additions make microbial communities less predictable (i.e., more stochastic; [43]) which was later further supported by an additional study [44]. In another study, Fodelianakis et al [45] showed that evolutionary drift in synthetic bacterial communities rendered them less predictable than in their original cultures.…”

Small‐scale spatial beta diversity of bacteria in the mixed upper layer of a lake

“…Some of these rare OTUs might have originated from small or fragmented particles that passed through the 5 μm pre‐filtration, highlighting the limitations of a simple operational division between FL and PA (Malfatti & Azam, 2009; Mestre et al, 2017). Rare ‘tychoplanktic’ bacteria also played a central role in the de‐novo formation of microbial biofilms from Lake Zurich waters (Silva & Pernthaler, 2020). Our findings indicate that the observed seasonal differences of community assembly processes in such biofilms might be related to the spatial heterogeneity of ‘tychoplanktic’ taxa and PA bacteria not retained by 5 μm pre‐filtration.…”