For many applications, these parameter values are an accurate representation of the conditions in which cultures will grow with the expected characteristics and at the expected rates. However, many applications have different requirements. For example, when studying a stressed cellular system, the ability to manipulate relative humidity is advantageous. When studying the effects of V. cholerae on human gastrointestinal cells, the manipulation of all three environmental variables, including RH, is required, because the stress on the cellular system can be more accurately defined by mimicking in the in vivo response to infection (i.e., dehydration).
As another example, psychrotrophic and thermophilic bacteria grow best at temperatures below and above (respectively) 37°C (e.g., psychrotrophs Vibrio marinus, Thiobacillus novellus, and Vibrio cholerae; and thermophiles Bacillus flavothermusand Thermus aquaticus), making the manipulation of the temperature variable critical for the growth of such cultures.
Technologies to provide precise, user-defined control of temperature and CO2 are widely available, so these two variables are commonly manipulated for experimental purposes; however, in most incubators, RH is not a parameter that is actively monitored and controlled, even though the manipulation of RH is a critical factor in cell growth. This directly impacts research validity and reliability by negatively impacting culture growth and making it less predictable.
