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日本語

Most of Antarctica is covered with thick snow and ice, but there are some ice-free areas, known as “Antarctic oases”, where the land is exposed. These ice-free areas occupy only about 0.2% of the area in Antarctica, but a variety of microorganisms have been observed. Two such areas, Langhovde and Skarvsnes, are close to Showa Station, Antarctica, and there are 50 or more lakes of various sizes in these areas (Fig. 1). Water at the bottom of these lakes remains unfrozen throughout the year and a unique ecosystem called “moss pillar,” that mainly includes moss and fungi, is distributed.

Assistant Prof. Yuu Hirose and others of the Department of Applied Chemistry and Life Science at Toyohashi University of Technology focused on the shores of freshwater lakes and also puddles and streams from snow meltwater. These environments are completely frozen during the winter season and accordingly are under more extreme stress (e.g. freezing and thawing and temperature changes), than those at the bottom of lakes.

In recent years, a technique for analyzing microbial community structure in environments using a next-generation sequencer has been developed. This method has a higher sensitivity and better quantitative properties than those of conventional techniques such as microscope observation. Assistant Prof. Hirose used this method to analyze microbial community structures at a total of 13 sites in the vicinity of Antarctic freshwater lakes (Fig. 2).

The results revealed that filamentous cyanobacteria were widely distributed, and also that the proportion of unicellular cyanobacteria and cyanobacteria with cell differentiation capacity (called heterocysts - cells dedicated to nitrogen fixation in filamentous cyanobacteria and formed mostly under nitrogen-deficient conditions) was small. The most widely distributed eukaryote was tardigrades with resistance to dryness and low temperatures. It was verified that specific eukaryotic algae such as cryptophyceae and green algae were dominant in some sites. There were also sites including nematodes feeding on algae. It is interesting that the fungi most dominant in moss pillars were not in the majority in these areas. The above results revealed that even in environments under extreme stress such as the borders of lakes or streams, a variety of organisms can survive.

It is expected that further study will be able to add greater clarity to the molecular mechanism that microorganisms living in these areas use to adapt to severe stresses. It is important to clarify the relationship between environmental factors, such as temperature and light conditions, and community structures of microorganisms. The monitoring and maintenance of the Antarctic ecosystem based on this information is also a valuable goal.

This work was supported by JSPS KAKENHI Grant Number JP15H05712, ""Plankton in polar regions -toward an understanding of their characteristics (representative: Naomi Harada)." The collection of samples was conducted as ordinary research observations of the 60th Japanese Antarctic Research Expedition.