Effect of temperature on growth parameters of psychrophilic bacteria and yeasts.

Three bacterial (Pedobacter heparinus, Pedobacter piscium, Pedobacter cryoconitis) and three yeast strains (Saccharomyces cerevisiae, Leucosporidiella creatinivora, Rhodotorula glacialis) of different thermal classes (mesophiles and psychrophiles) were tested for the effect of temperature on a range of growth parameters, including optical density, viable cell numbers, and cell dry mass, in order to determine the temperature conditions under which maximum biomass formation is obtained. Maximum values of growth parameters obtained at the stationary growth phase of the strains were used for statistical calculation. Temperature had a significant (P <or= 0.05) effect on all growth parameters for each strain; correlations between the growth parameters were significant (P <or= 0.05-0.01). The maximum growth temperature or the temperature at which microbial growth was fastest was in no case the temperature at which the investigated strains produced the highest amount of biomass. All tested psychrophilic bacteria and yeast strains produced highest amounts of cells (as calculated per mg cell dry mass or per OD(600) unit) at 1 degrees C, while cell numbers of mesophiles were highest at 20 degrees C. Thus, cultivation temperatures close to the maximum growth temperature are not appropriate for studying psychrophiles.