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

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.

Phytoplankton size-diversity mediates an emergent trade-off in ecosystem functioning for rare versus frequent disturbances

“…The model was set up to simulate semi-continuous batch cultures 28 32 with periodic nutrient additions. With each addition of nutrient-rich water, plankton are allowed to overflow (pulsed mortality) as some fraction of the volume of the incubation vessel is displaced.…”

“…Different levels of phytoplankton size diversity are sustained by adjusting a single parameter for either the TD or KTW formulation, respectively. For each level of diversity, the model is first allowed to equilibrate for a spin-up period (90 d) during which it simulates a batch incubation, and then the periodic disturbances are simulated by periodic nutrient additions as in semi-continuous batch cultures 28 32 . See the Methods for details.…”

Importance of mixotrophic bacterivory can be predicted by light and loss rates

“…Treatments were set up as continuous cultures with constant dilution rate, for which we employed a novel ‘chemostat‐like’ system, the “exponentially fed batch culture” (EFB; Fischer et al ). The EFB works like a chemostat without continuous outflow.…”

“…This provides the opportunity to take a fairly large sampling volume, relative to the culture volume, at regular intervals, while working with relatively small culture volumes. For details on the used materials and setup see Fischer et al (). All used materials were handled sterile.…”

Costs and benefits of toxin production in a dinoflagellate

“…Dinoflagellates cannot tolerate vigorous mixing (Berdalet et al 2007), and a classical chemostat cannot be used. Instead, we used exponentially fed batch cultures (EFB; Fischer et al 2014). The EFB is similar to a chemostat except that there is no continuous outflow.…”