Interspecific differences in cryoresistance of lichen symbiotic algae of genus Trebouxia assessed by cell viability and chlorophyll fluorescence

Unicellular algae of genus Trebouxia are the most frequent symbiotic photobionts found in lichen species adapted to extreme environments. When lichenised, they cope well with freezing temperature of polar regions, high-mountains environments and were successfully tested in open-space experiments. Tr...

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Bibliographic Details
Published in:	Cryobiology Vol. 64; no. 3; pp. 215 - 222
Main Authors:	HAJEK, J, VACZI, P, BARTAK, M, JAHNOVA, L
Format:	Journal Article
Language:	English
Published:	Kidlington Elsevier Inc 01-06-2012 Elsevier
Subjects:	Adaptation, Physiological Agar Algae Biological and medical sciences Chlorophyll Chlorophyll - chemistry Cooling protocols Cryopreservation Culture collections Culture Media Cyanobacteria - classification Cyanobacteria - isolation & purification Cyanobacteria - physiology Fluorescence Freezing Freezing temperature Fundamental and applied biological sciences. Psychology Lasallia pustulata Lichenes Lichenised algae Lichens Lichens - physiology Media (culture) Microbial Viability Nitrogen Photosynthesis Photosystem II Protein Complex - chemistry Plant cytology, morphology, systematics, chorology and evolution Quantum yield Shock Species Specificity Spectrometry, Fluorescence Sub-zero temperature Symbiosis Temperature effects Thalli Thallophyta Thawing Trebouxia Trebouxia erici Cooling protocols Freezing temperature Lichenised algae Sub-zero temperature Quantum yield Skin disease Temperature Cooling Cell survival Cold Algae Plant biology Tolerance Environmental factor Lichen Strain Cryobiology Photosynthesis Comparative study Biomedical engineering
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Summary:	Unicellular algae of genus Trebouxia are the most frequent symbiotic photobionts found in lichen species adapted to extreme environments. When lichenised, they cope well with freezing temperature of polar regions, high-mountains environments and were successfully tested in open-space experiments. Trebouxia sp. is considered potential model species for exobiological experiments. The aim of this paper is to evaluate cryoresistence of Trebouxia sp. when isolated from lichen thalli and cultivated on media. In our study, six algal strains were exposed to repeated freezing/thawing cycles. The strains of Trebouxia sp. (freshly isolated from lichen Lasallia pustulata), Trebouxia erici, Trebouxia asymmetrica, Trebouxia glomerata, Trebouxia irregularis, and Trebouxia jamesii from culture collection were cooled from 25 to −40°C at two different rates. The strains were also shock frozen in liquid nitrogen. After repeated treatment, the strains were inoculated and cultivated on a BBM agar for 7days. Then, cell viability was assessed as relative share of living cells. Potential quantum yield of photochemical reactions in PS II (FV/FM), and effective quantum yield of photochemical reactions in PS II (ΦPSII) were measured. While the slow cooling rate (0.5°Cmin−1) did not cause any change in viability, FV/FM, and ΦPSII, the fast cooling rate (6.0°Cmin−1) caused species-specific decrease in all parameters. The most pronounced interspecific differences in cryoresistance were found after shock freezing and consequent cultivation. While T. asymmetrica and T. jamesii exhibited low viability of living cells (18.9% and 34.7%) and full suppression of photosynthetic processes, the other strains had viability over 60%, and unaffected values of FV/FM, and ΦPSII. This indicated a high degree of cryoresistance of T. glomerata, T. erici, T. irregularis and Trebouxia sp. strains. These strains could be used for detailed investigation of underlying physiological mechanisms and as models for astrobiological tests taken in the Earth facilities.
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ISSN:	0011-2240 1090-2392
DOI:	10.1016/j.cryobiol.2012.02.002