STRESS RESPONSES - Cyanobacteria - page 708

Figure 21: Chroococcidiopsis sp. Picture courtesy G. L. Tiwari, Department of Botany, University of Allahabad, Allahabad-
211002, India.
Color image of this figure appears in the color plate section at the end of the topic.
Dried monolayers of Chroococcidiopsis sp. 029 strain could not survive the harsh simulated martian-
surface UV and visible light conditions as the cells were killed within 30 min but survived and
exhibited slow growth albeit for short periods beneath 1 mm rocks if supplied with water and
nutrients. Even after the cells had lost viability, enzymic activity and pigmentation there was no
change in the morphology of the cells (Cockell et al ., 2005). Raman spectroscopic analysis of the
cyanobacteria inhabiting the gypsum crystals from the Houghton Crater, Devon Island, Canadian
High Arctic (the site of meteorite impact during the Miocene 23 My ago) revealed the existence of
Nostoc and Gloeocapsa . Specifi c biosignatures developed for β-carotene and scytonemin in these
crystals would be helpful in the detection of extinct or extant halotrophs inside sulphate crystals
from Mars (Edwards et al ., 2005).
Epilithic and endolithic cyanobacteria growing on rocks from a limestone cliff in Beer, Devon,
U.K. have been identifi ed by culture-independent (16S rRNA sequencing) and culture-dependent
isolation techniques. Among the 92 clones identifi ed, the largest phylotype of 33 clones was distantly
related to Halothece sp. from marine environments. Morphotypes bearing resemblance to Leptolyngbya
(isolates OU-6, OU-8, OU-13 and OU-14), Phormidium (isolates OU-44 and OU-10) and a member of
Pleurocapsales (isolates OU-11 and OU-12) have been isolated. With a view to select cyanobacteria for
space missions, the rocks from the same site were exposed to the effects of low earth orbit at a height
of 300 km for 10 days. A single cyanobacterial isolate (OU-20) bearing morphological resemblance
to Gloeocapsa sp. survived the extreme radiation and desiccation conditions associated with space.
It was possible to select and isolate the same organism (OU-20) by exposing the rocks from the
same site to similar conditions of desiccation (0.7 x 10 -3 kPa), vacuum and UV light (325-400 nm for
different time intervals) under the laboratory conditions. Vacuum was found to be more detrimental
than desiccation (Olsson-Francis et al ., 2010).