Changestat Explained

Changestat is a continuous cultivation method that is used for acquiring quantitative data of a microorganism's metabolism at various environmental conditions within a single experiment. Every changestat always starts as a continuous cultivation experiment (chemostat, turbidostat), but after reaching steady state, smooth and slow change of an environmental parameter is applied. Two most common changestat techniques are accelerostat (A-stat) and dilution rate stat (D-stat).^{[1] [2]}

In case of A-stat the changing environmental parameter is dilution rate (D, h⁻¹) that causes the increase of specific growth rate (μ, h⁻¹). When the acceleration of dilution (a) is chosen correctly then D = μ as in chemostat. The problem of choosing the correct acceleration of dilution has been studied with Escherichia coli and Lactococcus lactis resulting recommended range of 0.01-0.005 h⁻².^{[3] [4]}

In D-stat dilution rate is always constant as in chemostat, but after reaching steady state environmental parameter other than dilution rate is changed. For instance temperature, pH or acetate concentration has been smoothly changed in bioreactor.^{[4] [5]} Turbidostat type changestats are called Z-auxoaccelerostats^[2] (pH-auxoaccelerostat, CO₂-auxoaccelerostat). In similar to D-stat after reaching steady state a selected environmental parameter is changed.

Notes and References

1. Paalme. Toomas. Kahru. Anne. Elken. Raul. Vanatalu. Kalju. Tiisma. Kalle. Raivo. Vilu. The computer-controlled continuous culture of Escherichia coli with smooth change of dilution rate (A-stat). Journal of Microbiological Methods. 1995. 24. 2. 145–153. 10.1016/0167-7012(95)00064-X.
2. Kasemets. Kaja. Drews. Monika. Nisamedtinov. Ildar. Adamberg. Kaarel. Paalme. Toomas. Modification of A-stat for the characterization of microorganisms.. Journal of Microbiological Methods. 2003. 55. 1. 187–200. 10.1016/S0167-7012(03)00143-X. 14500010.
3. Lahtvee. Petri-Jaan. Adamberg. Kaarel. Arike. Liisa. Nahku. Ranno. Aller. Kadri. Vilu. Ranno. Multi-omics approach to study the growth efficiency and amino acid metabolism in Lactococcus lactis at various specific growth rates.. Microbial Cell Factories. 2011. 10. 12. 10.1186/1475-2859-10-12. 21349178. 3049130 . free .
4. Valgepea. Kaspar. Adamberg. Kaarel. Nahku. Ranno. Lahtvee. Petri-Jaan. Arike. Liisa. Vilu. Ranno. Systems biology approach reveals that overflow metabolism of acetate in Escherichia coli is triggered by carbon catabolite repression of acetyl-CoA synthetase.. BMC Systems Biology. 2010. 4. 166. 10.1186/1752-0509-4-166. 21122111. 3014970 . free .
5. Lahtvee. Petri-Jaan. Valgepea. Kaspar. Nahku. Ranno. Abner. Kristo. Adamberg. Kaarel. Vilu. Raivo. Steady state growth space study of Lactococcus lactis in D-stat cultures.. Antonie van Leeuwenhoek. 2009. 96. 4. 487–96. 10.1007/s10482-009-9363-2. 19603284. 1002666.