Journal Article Diversity of proteolytic microbes isolated from Antarctic freshwater lakes and characteristics of their cold-active proteases

13pp.82 - 90 , 2017-09
ISSN:18739652
Description
Despite being an extreme environment, the water temperature of freshwater lakes in Antarctica reaches 10 °C in summer, accelerating biological activity. In these environments, proteolytic microbial decomposers may play a large role in protein hydrolysis. We isolated 71 microbial strains showing proteolytic activity at 4 °C from three Antarctic freshwater lakes. They were classified as bacteria (63 isolates) and eukaryotes (8 isolates). The bacterial isolates were classified into the genera Flavobacterium (28 isolates), Pseudomonas (14 isolates), Arthrobacter (10 isolates), Psychrobacter (7 isolates), Cryobacterium (2 isolates), Hymenobacter (1 isolate), and Polaromonas (1 isolate). Five isolates of Flavobacterium and one of Hymenobacter seemed to belong to novel species. All eukaryotic isolates belonged to Glaciozyma antarctica, a psychrophilic yeast species originally isolated from the Weddell Sea near the Joinville Island, Antarctica. A half of representative strains were psychrophilic and did not grow at temperatures above 25 °C. The protease secreted by Pseudomonas prosekii strain ANS4-1 showed the highest activity among all proteases from representative isolates. The results of inhibitor tests indicated that nearly all the isolates secreted metalloproteases. Proteases from four representative isolates retained more than 30% maximal activity at 0 °C. These results expand our knowledge about microbial protein degradation in Antarctic freshwater lakes.
南極湖沼における有機物循環についてより深く理解するために、3つの南極淡水湖から4°Cでタンパク質分解活性を示す微生物71株を分離し、分類学的解析と代表株が分泌するプロテアーゼの解析を行った。分子系統解析の結果、63株は7属15種の細菌に、8株は単一種の酵母菌に分類された。代表株の約半数は25°Cでは生育しない好冷菌であり、そのうち4株が産生するプロテアーゼは、0°Cにおいても各最大活性の30%以上の比活性を示した。また、プロテアーゼ阻害剤を用いた解析の結果、ほぼ全ての代表株がメタロプロテアーゼを分泌することがわかった。本研究により、南極淡水湖におけるタンパク質の微生物分解に関する知見が広げられた。

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