Microbiological Review on Hot Spring Sciences in Japan.

This is a review of microbes which live in extreme environments. We focused on natural hot springs with high temperatures and/or acidic environments. Rod shaped bacterium, Bacillus acidocaldarius with spores from Kuroyu, Akita Prefecture were cultured at 55°C under acidic conditions. Sulfur-oxidizing bacteria were cultured from Yunohanazawa, Kanagawa Prefecture. These bacteria were associated with the quality of sulfur in the springs' flow. Irregularly formed archaea were cultured at 70°C under acidic condition from a hot spring pool in the Hakone-Oowakudani geothermal area. The strain was a new species, which was then named Metallosphaera hakonensis. Then, bacterial and archaeal community structures in Japanese hot springs were revealed by 16 rRNA clone library analyses. It has been noted that only a small fraction (<1%) of the microorganisms found in nature can be cultured using traditional cultivation methods. Therefore, a culture independent method, 16S clone library analysis is useful method to reveal the bacterial and archaeal communities. For example, Satoh et al analyzed and compared the 16S rRNA gene compositions and environmental factors of four distinct solfataric acidic hot springs in Kirishima, Japan. As a result, species compositions and biodiversity were clearly different between the ponds showing different temperatures and dissolved elemental concentrations. Moreover, hot spring microalgae such as cyanobacteria, green algae, diatoms and red algae were examined. They live in about 20°C to 80°C, and in acid (pH2-3), neutral (pH6-7), and week alkaline (pH8-9) conditions. Unicellular red algae Cyanidium caldarium, Galdieria sulphuraria, and diatom Pinnularia sp. live in acid hot springs such as Noboribetsu hot springs, Hokkaido and Kusatsu hot springs, Gunma prefecture. Cyanobacteria Mastigocladus sp., Phormidium sp., and Oscillatoria sp. live in neutral and weak alkaline hot springs such as Shima hot springs, Gunma prefecture, Tsurunoyu hot springs, Akita prefecture, and Atagawa hot springs, Shizuoka prefecture. Micro algae capable of photosynthesis form the hot spring ecosystem among bacteria, protozoa and other microorganisms. [ABSTRACT FROM AUTHOR]