Changestat is a continuous cultivation method that is used for acquiring quantitative data of a
microorganism
A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...
's
metabolism
Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
at various environmental conditions within a single experiment. Every changestat always starts as a continuous cultivation experiment (
chemostat
A chemostat (from ''chem''ical environment is ''stat''ic) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms is continuously removed at the s ...
,
turbidostat), but after reaching
steady state
In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties ''p' ...
, 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).
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
A chemostat (from ''chem''ical environment is ''stat''ic) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms is continuously removed at the s ...
. 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.
In D-stat dilution rate is always constant as in
chemostat
A chemostat (from ''chem''ical environment is ''stat''ic) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms is continuously removed at the s ...
, but after reaching
steady state
In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties ''p' ...
environmental parameter other than dilution rate is changed. For instance temperature, pH or acetate concentration has been smoothly changed in
bioreactor
A bioreactor is any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, biochem ...
.
[ (pH-auxoaccelerostat, CO2-auxoaccelerostat). In similar to D-stat after reaching ]steady state
In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties ''p' ...
a selected environmental parameter is changed.
References
{{reflist
Microbiology