STRESS RESPONSES - Cyanobacteria - page 710

desert in Arizona, N. America (that receives summer monsoons) the cyanobacteria are represented
by species of Lyngbya , Calothrix , Schizothrix and Nostoc . In the cold deserts of N. America, the crusts
are dominated by M . vaginatus . The cold deserts of N. America (Pacifi c North west where summers
are hot and dry and winters are cool and moist) support the growth of either attached or vagrant
forms of Dermatocarpon miniatum , N . commune and N . fl agelliforme . The soil crusts in the regions of
sub-Alpine, Alpine sods and Arctic tundras characteristically support the growth of Nostoc sp. The
soil crusts of Californian Chaparrals (Mediterranean dry steppe) support the growth of Schizothrix
and Nostoc (Belnap et al ., 2001b). The soil crusts from the cool and cold deserts of the Colorado
Plateau are dominated by species of Microcoleus ( M . vaginatus Gomont), Phormidium and Schizothrix
(Garcia-Pichel et al ., 2001). Microbial mats from Hunt Ice Shelf, High Arctic, Canada (latitude 83º
04'N, longitude 74º25'W) are dominated by the growth of Phormidium , Leptolyngbya , Nostoc and
Gloeocapsa among other heterotrophic bacteria, green microalgae, diatoms and microinvertebrates
(Vincent et al ., 2000, 2004; Mueller et al ., 2005).
The tropical soil crusts of India are dominated by the growth of Lyngbya arboricola , Plectonema
notatum , Scytonema chiastum and S . ocellatum among many other non-heterocystous and heterocystous
cyanobacteria that appeared in cultures associated with these forms (Tirkey and Adhikary, 2005).
Other terrestrial crusts grow on common building surfaces/roof tops or archaeological monuments.
Species of Gloeocapsa , Gloeothece , Aphanocapsa , Chroococcus , Scytonema ( S . geitleri ) and Tolypothrix have
been reported from building surfaces/roof tops (Tripathi et al ., 1991). L . arboricola has been reported
from the bark surfaces of Mangifera indica as well (Tripathi and Srivastava, 2001). The growth of
species of Tolypothrix ( T . scytonemoides ), Calothrix and Nostoc is a common feature on the surface
of temple rocks in India (Amarpalli et al ., 1997; Tripathy et al ., 1997, 1999). Some of the dominant
cyanobacterial species growing on the temple rocks of India are presented in Fig. 23. Deterioration of
stone monuments of cultural heritage in European countries of the Mediterranean Basin caused by
cyanobacteria and certain members of Chlorophyta has been reviewed. Lithophytic cyanobacterial
species belonging to the genera Gloeocapsa , Gloeothece , Chroococcus , Phormidium , Plectonema , Scytonema ,
Lyngbya and Microcoleus have been recorded from six types of rocks (marble, limestone, travertine,
dolomite, sandstone and granite) (Macedo et al ., 2009).
In studies dealing with desiccation, the dried mats of soil crusts are often used directly. Besides
strains of Chroococcidiopsis , the most widely employed cyanobacterium to understand desiccation
tolerance is N . commune . It is cosmopolitan in its distribution and occurs in terrestrial habitats such
as rice fi elds (grows as sheres and the balls attain varying diameters up to 10 cm), nutrient poor soils
and limestones (grows as parchament-like colonies) and assumes macroscopic proportions. An edible
form of Nostoc (known as Ge-Xian-Mi in Chinese) identifi ed as N . fl agelliforme was reported from
arid and semi-arid regions of China (Gao, 1998) and rice fi elds of Hefeng County of China (Qiu et al .,
2002). This form has been identifi ed as N . sphaeroides (Huang et al ., 1998) and N . commune (Martinez
and Querijero, 1986; Martinez, 1988; Potts, 2000). Colonies of N . commune either collected from the
fi eld or its clonal isolates are employed in studies devoted to desiccation tolerance [see Fig. 6 (D) of
Chapter 1]. This organism has been reported to survive storage at -400 MPa (0% relative humidity)
for centuries (Potts, 1994) and the desiccated samples for at least 64 years have been reported to
be viable and cultures obtained there from (Shirkey et al ., 2003). The fi laments are immobilized in
the unusual EPS that contributes in many ways for its reported desiccation tolerance. The presence
of two antibacterial metabolites (a terpenoid, anthroquinone) in N . commune (EAWAG 122b) and
carotenoids, 2-hydroxymyxol-2'-fucoside, nostoxanthin and canthaxanthin in N . commune NIES
(IAM M-13) make this organism unique (Jaki et al ., 2000; Takaichi et al ., 2009). Thus N . commune is a
typical anhydrobiotic cell and has been developed as a prokaryotic model for answering fundamental