TAXONOMY, PHYLOGENY AND EVOLUTION - Cyanobacteria - page 47

power of this technique in the differentiation of different genotypes of Microcystis has been stressed.
Floyd et al . (2005) analysed the holdings of prokaryotes at the American Type Culture Collection
(ATCC) with regard to the geographical and environmental habitats from which they were isolated.
A comparison of the selected habitats in the recently published literature on culture-independent
assays on microbial diversity revealed as to how the cultured members existing in ATCC are
distributed in nature. Of the 37 environmental habitats, isolates from soil were maximum (27.3%),
followed by those from host-associated, terrestrial, plant (16.0%) and lastly from food and food-
processing associated (7.3%) habitats. The origin of nearly 41.4% of the cultures (2,209 entries) is not
known. Isolates from N. America were 24.1% (1289 entries) followed by those from Europe (14.7%
and 784 entries) and lastly from Asia (11.5% and 612 entries). A comparison of the number of known
microbial species in biodiversity hotspots from various continents revealed maximum number of
species (314) from Europe and Central Asia, followed by 138 microbial species from Mainland Asia
(Indo-Burma region of hotspot). Microcystin synthetase ( mcy A gene) was chosen as the molecular
marker for the quantifi cation of toxic cyanobacteria from polluted waters with the help of a novel
primer MSR-2R by conducting a real-time PCR. A direct correlation existed between the number of
cells in the culture and those determined by PCR. The detection limit has been found to be 8.8 cells
per reaction. The gene could be successfully amplifi ed and quantifi ed from environmental samples
(Furukawa et al ., 2006).
Kim et al . (2006) determined the cyanobacterial diversity during algal blooms in Daechung
reservoir, Korea on the basis of cpcBA - IGS sequences from environmental samples. Sequences of
Microcystis , Aphanizomenon ( Anabaena ), Pseudoanabaena and Planktothrix ( Oscillatoria )-like groups and
three other previously reported cpcBA - IGS sequences have been detected during the peak of bloom
growth. The succession of the cyanobacteria based on cpcBA - IGS sequences is further supported by
PCR-DGGE of 16S rRNA genes. Boutte et al . (2006) tested the utility of specifi c 16S rRNA cyanobacterial
primers CYA 359F, CYA 781R(a) and CYA 781R(b) to assess molecular diversity of cyanobacteria
from their natural habitats. CYA 781R(a) preferentially targeted fi lamentous cyanobacteria whereas
CYA 781R(b) targeted unicellular cyanobacteria. Environmental nifH (encoding reductase subunit of
nitrogenase) gene sequences from the biological soil crusts of Colorado Plateau, USA revealed the
existence of three distinct clades of heterocystous cyanobacteria. These sequences matched up to
nearly 89% with the nifH gene sequences of cultured heterocystous cyanobacteria Nostoc commune ,
Scytonema hyalinum , Tolypothrix and Spirirestis . These constituted the dominant members of this
habitat (Yeager et al ., 2007).
Valério et al . (2009) identifi ed 118 cyanobacterial isolates from Portuguese freshwater reservoirs
belonging to Chroococcales (54), Oscillatoriales (15) and Nostocales (49). Cluster analysis of STRR and
LTRR sequences, PCR fi ngerprinting profi les were obtained and these were subjected to molecular
identifi cation at the species level. Based on16S rRNA and rpoC1 phylogenies a diagnostic key for
the identifi cation of cyanobacteria based on 16S rRNA-ARDRA, ITS amplifi cation and ITS-ARDRA
has been proposed. Planktothrix agardhii showed lowest diversity and Aph. fl os-aquae has the highest
diversity. Prabina et al . (2005) has used RAPD fi ngerprinting as a tool for checking genetic purity
of cyanobacterial strains. In most of these studies, more than ten primers were used to generate
RAPD patterns. Phylogenetic analysis of 12 cyanobacterial strains belonging to Oscillatoriaceae (8 of
Oscillatoria and 4 of Lyngbya ) by random amplifi cation of polymorphic DNA revealed the presence
of two major clusters. One of these clusters is composed of O. obscura and in the second the rest of
the cyanobacterial strains have clustered together (Perumal et al ., 2009).