The exponentially fed batch culture as a reliable alternative to conventional chemostats

Robert Fischer, Tom Andersen, Helmut Hillebrand, Robert Ptacnik

Limnol. Oceanogr. Methods 12:432-440 (2014) | DOI: 10.4319/lom.2014.12.432

ABSTRACT: Chemostats and their common alternative, semicontinuous cultures, play a pivotal role as model systems in aquatic ecology. Despite the theoretical and conceptual advantages chemostat systems offer, they can be challenging to set up and operate. One such challenge is to obtain a representative sample volume without changing the dilution rate, another is to ensure that the outflow constitutes an unbiased loss of the chemostat contents. Here, we present a specific system, the exponentially fed-batch culture (EFB), as an economic, simply operable albeit reliable alternative to conventional chemostats. The EFB is well-known in biotechnological research and in industrial bioengineering. Like a conventional chemostat, the EFB culture is a continuous culture method. In contrast to a conventional chemostat, there is no outflow. To ensure a constant dilution rate and therefore steady state, fresh medium is continuously supplied proportional to the current culture volume. Hence culture volume and medium supply rate both increase exponentially with time until sampling, when the volume is set back to the initial state. This allows taking large sample volumes without disturbing the steady state of the experimental unit. Here we compare the performance of the exponentially fed-batch culture with a conventional chemostat and a semicontinuous system by growing a green algae until steady state is reached. Most pronounced differences were found between semicontinuous system and the two continuous methods. Results from the EFB and chemostat were very similar. However, a bias in the sampling of the chemostat resulted in accumulation of biomass relative to the EFB.