APPLICATIONS / BANG-BANG TURBIDOSTAT

Why use a Bang-Bang Turbidostat?

Understanding how the rate of growth of your organism is impacted by process conditions is a key part of screening media, strains and process optimisation.

Monitoring growth rates in shake flasks is incredibly time consuming requiring many flasks and different incubators to produce data that is, despite the huge effort, relatively low resolution.

Ogi3 automates this process to condense multiple flasks and many hours of work into one longitudinal experiment to produce richer, more robust data without the risk of culture contamination.

Each Ogi3 Reactor Flask is connected to two 500 mL laboratory bottles, one containing fresh culture media, e.g. LB, and the other being for removed ‘waste’ culture material, using lengths of peristaltic pump tubing and Media/Waste Stoppers.

When an experiment is configured an upper and lower OD value can be set for each of the four reactor flasks in the system.  As the culture grows the OD is measured as frequently as every 3 minutes.  When the OD of a culture reaches the upper OD threshold the feed and drain pumps are activated to supply fresh culture media to the culture while removing excess volume which dilutes the culture while maintaining a culture volume of 15 mL in the reactor flask.

After each pumping action the OD of the culture is checked and, if needed, the pumping action will be repeated until the OD reaches the lower OD threshold.  Upon reaching the lower OD threshold the culture will then grow in ‘batch’ mode until the upper OD threshold is reached and the process repeated.

The duration of the experiment is user-defined with the potential number of cycles unlimited.  Additionally, process changes can be implemented during the course of the experiment to explore the impact of the change on the rate of growth.

The above plot shows six cycles of a single bang-bang turbidostat culture grown between OD of 0.1 and 0.4.  During the growth phase the OD was measured every 5 minutes as shown by the black dots, providing 12 OD readings for each growth cycle.  Note that during the dilution phase the OD readings are more frequent, occurring after each pump action.

In this experiment the impact of temperature on growth rate was also assessed with the temperature being increased from 30°C to 37°C

The resulting plot of the growth rates shows a clear picture of the impact of temperature on the growth rate.

Any of the process parameters, such as stirring speed and pH, could also be adjusted to assess the impact.  Additionally, the system can be programmed to change/make an addition to the culture at a defined time point as shown below

The above plot shows a bang-bang turbidostat culture grown between OD of 0.2 and 0.3.  Initially the culture is grown in MM9 culture media with glycerol as the carbon source and then automatically switched to MM9 with glucose as the carbon source after ~31 hours as indicated by the arrow.

Following a period of adaptation the difference in the rate of growth is clearly visible in the below plot.

NB: Images not to scale