Temperature spans for growth: Hypothesis and discussion

Abstract

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’.

Acetoclastic and hydrogenotrophic methane production and methanogenic populations in an acidic West‐Siberian peat bog

“…Methane emission fluxes were registered at all research sites. The optimal conditions for CH 4 production were found to be pH 5.0–5.5 and temperatures of 20–25°C, so that the microbial methanogenic community can be classified as acidophilic psychroactive (Wiegel, 1990; Johnson, 1998). The optimum changed to neutral pH when the samples were incubated for prolonged periods at increased pH values, indicating that neutrophilic microorganisms were also present in the peat.…”

Physiological response to temperature changes of the marine, sulfate-reducing bacterium Desulfobacterium autotrophicum

“…Only psychrotolerant microorganisms are active over this temperature range. They have an optimal growth temperature above 20°C, but are also able to grow below 5°C [3]. Psychrophilic microorganisms can even grow below 0°C, but they cannot grow above 20°C, and have an optimal growth temperature below 15°C.…”

Diversity of Thermophilic Anaerobes

“…Thermophilic prokaryotes able to grow over a 35°C–40°C temperature span are considered temperature‐tolerant thermophiles 57 . To the authors' knowledge, the record widest temperature growth range is 22°C–75°C by a Methanothermobacter thermautotrophicus –like strain isolated from river sediment (J. Wiegel, unpublished results).By comparison, some thermophilic anaerobes are reported to have especially narrow temperature growth ranges, such as 42°C–55°C for Anaerolinea thermolimosa 59 and 50°C–60°C for Anaerolinea thermophila 60 —two species from the family Anaerolinaceae { B 27}.…”

“…In cases where thermophilic and mesophilic species exist within a genus, the ability to grow at elevated temperatures occurs via combinations of different properties, including the stabilization of intracellular compounds through binding of cations, such as Ca 2+ ; the insertion of additional hydrogen bridges in protein structures via the presence of increased acidic amino acids (e.g., by substituting glutamine with glutamic acid); the formation of more globular protein structures with additional hydrophobic regions inside; the stabilization of membrane fluidity by changes in fatty acid lengths and branching 65 ; and changes in proton permeability of the cytoplasmic membranes 66 . In cases where the addition of genes conferred higher growth temperatures, it is assumed that the enzymes encoded by these genes removed the bottleneck of otherwise cryptic thermophiles 57,67 …”