TEMPERATURE SPANS FOR GROWTH - HYPOTHESIS AND DISCUSSION

In recent years the upper and lower temperature limits for growth of pure cultures of microorganisms have been extended at least to 110°C and -14°C, respectively. There are no organisms which grow at both 0°C and 100°C and, therefore, organisms are grouped according to their ranges of growth temperatures. Thus, the questions of importance are:: (1) What is the widest temperature range (temperature span) over which a single organism can grow? and (2) How much can one alter the temperature spans of an organism? The concept of 'cryptic thermophiles' is used to explain some of the published data on the latter question. A wider temperature range can be very important for organisms in various ways, since it makes an organism more versatile with regard to changes in the environment. Also, it enables the organism to utilize a wider range of ecological niches. Some aerobic and anaerobic extreme thermophiles will grow within a span of more than 40°C. Furthermore, such organisms are regarded suitable for biotechnological applications as well. The following hypothesis is presented and discussed: these organisms have two sets of key enzymes, and their synthesis is regulated by temperature. Such organisms are capable of growing in two different ranges, such as the mesophilic and thermophilic ranges. The hypothesis is based on the fact that these bacteria exhibit broken Arrhenius plots (growth temperature versus) doubling time as parameters), and is illustrated with 'temperature tolerant extreme thermophiles' as the major example. However, the hypothesis is not restricted to this group, but is also applicable to the 'temperature tolerant thermophiles and mesophiles'. © 1990.