Temperature Characteristics of Psychrotrophic and Psychrophilic Bacteria

When the Arrhenius equation is applied to microbial growth rates, a temperature characteristic (μA) represents the activation energy. While these μA values describe the energetics favouring growth, there is still no convincing evidence from empirical data to support the idea of a widely applicable relationship between μA values and optimal growth temperatures, which may serve as a basis for the classification of psychrophiles, psychrotrophs, mesophiles and thermophiles. The μA values for the exponential growth rates of 16 psychrophilic and psychrotrophic bacterial strains, including 9 from the literature, varied from 3 to 33 (kcal mol−1). A plot of μA versus growth temperature optimum deviated considerably from empirical equations reported recently ( Mohr & Krawiec, 1980 ) for a different selection of strains. Moreover, Arrhenius profiles with two distinct slopes at suboptimal temperatures were not restricted to bacteria with growth temperature optima higher than 37 °C, as had been suggested in that report. A psychrotrophic strain of Cytophaga johnsonae with a growth temperature optimum of 23–25 °C was characterized by two different temperature characteristics. Furthermore, in the upper range of suboptimal temperatures (11–24 °C), temperature characteristics (μA1) were also affected by temperature acclimation of the inoculum.