Abstract

Co-authors: Eulyn Pagaling1,2*, Katsiaryna Usachova1,3, Liudmila Usachova4, Fiona Strathdee1, Kristin Vassileva1, Rocky Kindt1, Rosalind J. Allen2

The ability to control and engineer complex microbial communities for particular purposes or functions depends on the reproducibility and stability of community structure and function under controlled conditions. Natural microbial communities contain many low-abundance species, comprising the so-called “rare biosphere”, which may be selected when the environmental parameters governing the system are altered. Current data suggest that the stochastic selection of rare species, together with the complex, non-linear dynamics of these communities, can lead to unpredictability of community structure and function following environmental selection. This can also result in alternative stable states of the system which may be difficult to interconvert.

We give an example of a wastewater treatment plant processing urban waste streams, describing the operational problems caused by the emergence of stable undesirable community states and challenges in recovering the diversity, structure and function. We then investigate the phenomena of alternative states and unpredictability using a simple, replicable laboratory model system (microcosm) containing diverse microbial ecotypes which cycle nutrients such as carbon and sulphur compounds and generate community function in the form of a redox potential gradient. Variability in the microbial community composition of this model system is observed following a selective bottleneck in the system caused by anaerobiosis. Concomitant variation in the development of the redox gradient is also seen. However, stable final microcosm communities re-inoculated into the same environment exhibit much less variability than the original communities and a final organisational state which is closely related to their initial state at inoculation. These results suggest that selection under novel environmental conditions can cause unpredictability in microbial community structure and function, but that repeated selection can be a means to ensure predictability. We discuss these phenomena with reference to microbial photobioreactor systems containing low microbial diversity which are amenable to engineering by “synthetic ecology”.