Alternative cold response modes in Chlorella (Chlorophyta, Trebouxiophyceae) from Antarctica

Abstract

H. Hu, H. Li and X. Xu. 2008. Alternative cold response modes in Chlorella (Chlorophyta, Trebouxiophyceae) from Antarctica. Phycologia 47: 28–34. DOI: 10.2216/07-28.1

Chlorella was known to show enhanced antifreeze capability after cold hardening. We isolated Chlorella strains NJ-7 and NJ-18, which display alternative cold response modes from rock surfaces in Antarctica. On the basis of 18S ribosomal (rRNA) sequences, NJ-7 is an Antarctic type of Chlorella vulgaris; NJ-18 is also a ‘true’ Chlorella species but differs from any previously reported species in structure. NJ-7 partially retained the enhancing effects of low temperature cultivation on freeze tolerance, which correlates with an increase of C18:3-fatty acid content and up-regulation of two antifreeze protein genes. NJ-18, however, showed stable freeze tolerance regardless of the pre-cultivation temperature. We propose that cold response modes vary widely in Chlorella and that the adaptation of C. vulgaris to Antarctica may serve as a model system for the evolution of antifreeze mechanisms in a single species of photosynthetic microorganism.

Key Words::

• Antarctica
• Antifreeze
• Chlorella
• Cold response modes

ACKNOWLEDGMENTS

This research was supported by the National Key Basic Research Project of China (2004CB719605), National Natural Science Foundation of China (No. 40606004) and Key Project (KSCX2-SW-332) of Knowledge Innovation Program of Chinese Academy of Sciences.