Thermophilic Bacteria Among Arctic, Subarctic, and Alpine Habitats

Abstract

Arctic, subarctic, and alpine regions support widely distributed populations of thermophilic bacteria among habitats where ambient temperatures vary from below lower psychrophilic to above upper thermophilic ranges. Although spore-forming bacilli are the most prevalent thermophiles, large numbers [290 to 1000 Colony Forming Units (CFUs) per g dry wt] of thermophilic actinomycetes were found in soils from parks in Reyjkavik, Iceland. Soils from arctic Greenland and alpine Colorado exhibited low numbers of thermophilic microorganisms (0 to 20 and 1 to 19 CFUs per g dry wt, respectively), but generally supported between 10³-and 10⁶-times larger mesophile and psychrotroph populations. With two exceptions, lagoon sediments from arctic Alaska possessed larger numbers of thermophilic bacteria than the adjacent soils we sampled during 1955–1957. Cultivated soils from Tromsø, Norway, showed greater thermophilic populations than nearby undisturbed soils (250 to 24,000 vs. 0 to 6700 CFUs per g dry wt); cultivation also increased numbers of mesophiles but not of psychrotrophs. Among 22 of 30 samples from geothermal areas of Iceland, thermophiles ranged from 1500 to 23,000 CFUs per g dry wt, and the ratios of thermophiles to mesophiles and psychrotrophs were much more compressed than from previously mentioned habitats. Thermophilic bacteria also were found in all but one of the volcanic and nongeothermal soils from Iceland (9 to 1500 and 22 to 19,000 CFUs per g dry wt, respectively), and a greater number of mesophiles and psychrotrophs were generally present in each case.

Spore-forming, thermophilic bacteria make up part of the microbiota of polar, subpolar, and alpine ecosystems. Although geothermal habitats at temperature extremes may support the growth of stenothermophiles, and microhabitats exist with temperatures in the optimal range for the reproduction of eurithermophiles, until in situ methods are available for studying the specific contribution of thermophilic microorganisms to the metabolic activity of the total microbiota, their quantitative contribution to the ecology and economy of arctic, subarctic, and alpine habitats cannot be elucidated.