Building up chemostats for experimental eco-evolutionary studies v2
Authors: Del Arco Ana , Woltermann Noemi , Becks Lutz 
Published: April 2020

Chemostats and other flow through culture systems are a powerful tool for the study of microbial and plankton communities in experimental ecology and evolutionary studies. Commercially available chemostat systems allow the control of a large number of parameters (e.g., ph, pressure, CO2 concentration) but are often expensive and offer a high level of control that is often not needed for many experimental studies. Non-commercial chemostats are more cost efficient, easily set up and flexible in volumes used. Different from semi-continuous culture systems, the flow through conditions of chemostats allow a constant inflow of resources from a reservoir (medium bottle) and outflow of unused nutrients, waste products and organisms, which are all collected in a waste bottle. Nutrient levels in the reservoir and the flow rate of the chemostat system (often referred to as dilution rate and presented as the fraction of the volume of the chemostat that is replaced per day) determines population growth rates and dynamics (for the theory behind chemostats see Smith & Waltman, 1995 and Weitz, 2015). Chemostats have been used in a number of studies and with different organisms and combinations of organisms. For example, Boer et al. (2010) studied how growth-limiting intracellular metabolites control yeast growth under diverse nutrient availability (Saccharomyces cerevisiae growing under five different nutrient supply of nitrogen: carbon: phosphorus). Becks et al. (2005) used chemostat systems to show how changes in the flow rate of a chemostat system influences the population dynamics of a three species microbial system. Frickel et al. (2016) used chemostats to investigate eco- evolutionary dynamics in a coevolving host-virus system (algae Chlorella variabilis and Chlorovirus strain PBCV-1) for 90 days. We present here an instruction for a cost efficient and flexible chemostat systems. These chemostats are composed of four main parts: a syringe unit, a glass bottle (i.e. the chemostat), a medium bottle and a waste bottle, all connected by tubing. A peristaltic pump and a low overpressure in the system allow the flow of medium from the reservoir to the chemostat bottle and of unused nutrients, waste products and organisms to the waste bottle. Chemostats are put on stirring plates to create a homogenosus environment within. Becks, L., Hilker, F.M., Malchow, H., Jürgens, K., Arndt, H., 2005. Experimental demonstration of chaos in a microbial food web. Nature 435, 1226–1229. https://doi.org/10.1038/nature03627 Boer, V.M., Crutchfield, C.A., Bradley, P.H., Botstein, D., Rabinowitz, J.D., 2010. Growth-limiting Intracellular Metabolites in Yeast Growing under Diverse Nutrient Limitations 21, 198–211. https://doi.org/10.1091/mbc.E09 Frickel, J., Sieber, M., Becks, L., 2016. Eco-evolutionary dynamics in a coevolving host – virus system. Ecol. Lett. 19, 450–459. https://doi.org/10.1111/ele.12580 Smith, H., Waltman, P., 1995.The Theory of the Chemostat: Dynamics of Microbial Competition (Cambridge Studies in Mathematical Biology). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511530043 Weitz, J.S. 2015. Quantitative Viral Ecology. Dynamics of viruses and their microbial host. Princeton University Press. ISBN: 9780691161549