Abstract
Microbial biofilms are ubiquitous in aquatic environments where they provide important ecosystem functions. A key property believed to influence the community structure and function of biofilms is thickness. However, since biofilm thickness is inextricably linked to external factors such as water flow, temperature, development age and nutrient conditions, its importance is difficult to quantify. Here, we designed an experimental system in a wastewater treatment plant whereby nitrifying biofilms with different thicknesses (50 or 400 µm) were grown in a single reactor, and thus subjected to identical external conditions. The 50 and 400 µm biofilm communities were significantly different. This beta-diversity between biofilms of different thickness was primarily caused by deterministic factors. Turnover (species replacement) contributed more than nestedness (species loss) to the beta-diversity, i.e. the 50 µm communities were not simply a subset of the 400 µm communities. Moreover, the two communities differed in the composition of nitrogen-transforming bacteria and in nitrogen transformation rates. The study illustrates that biofilm thickness alone is a key driver for community composition and ecosystem function, which has implications for biotechnological applications and for our general understanding of biofilm ecology.
Highlights
Biofilms are dense communities, encased in a polymer matrix, attached to a surface and/or each other[1] with a high microbial diversity compared to the bulk water system[1,2,3]
If local communities are further exposed to stochastic dispersal from the regional species pool, the expected result is that the abundance of a taxon in a local community can be predicted based on its respective abundance in the regional species pool and thereby follows neutral distribution patterns[8,9]
A null model approach was used to investigate if the differences in beta-diversity between Z50 and Z400 were due to deterministic or stochastic processes while accounting for the large differences in richness between Z50 and Z40043
Summary
Biofilms are dense communities, encased in a polymer matrix, attached to a surface and/or each other[1] with a high microbial diversity compared to the bulk water system[1,2,3]. Selection has been suggested as the major mechanism for community assembly in stream biofilms[10,11,12], and other biofilms[13], while for biofilms within lakes linked by dispersal, both stochastic and deterministic factors were shown to be important[14]. The importance of both stochastic and deterministic factors was shown in an elegant study using parallel microbial electrolysis cells incubated with wastewater[15]. Microorganism with deterministic dispersal might show preference towards different types of biofilms
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