CYANOBACTERIAL TOXINS - Cyanobacteria - page 559

cyanobacterial DNA from Lake Ontario (bordering Ontario, Canada and New York, USA) revealed
the existence of Microcystis , Planktothrix and Anabaena sp. at 50% of the sampling stations. With the
predominance of Microcystis sp. the MC concentration of the waters exceeded the WHO guidelines
(Hotto et al ., 2007). A metagenomic approach by the isolation of 36 kb DNA fragments containing
mcyA2 and mcyB1 genes from natural water samples and a correlation of these loci from individual
cyanobacterial cells improved the analysis of MC-producing strains in the Laurentian Great Lakes
(Allender et al ., 2009).
Asia : Amongst Asian countries, blooms of toxic cyanobacteria have been reported from South
Korea, China, Japan, Phillippines and Africa. Species of Microcystis , Anabaena , and Planktothrix /
Oscillatoria producing MCs and anatoxin-a have been predominantly represented from South Korean
drinking water resources (Oh et al ., 2001; Park, 2001). Yu (1989) conducted an epidemiological
study of human primary liver cancer in Qidong county in China and observed a correlation on the
incidence of liver cancer about eight times in people who used pond and ditch water for drinking
purposes. MC-producing species of Anabaena and Oscillatoria were detected in the ponds and
ditches in Haimen City (Jian-Su province) and Fusui county (Guangxi province) in China and a
signifi cant correlation between the occurrence of these bloom species and the incidence of primary
liver cancer has been established (Ueno et al ., 1996; Xu et al ., 2000). Lake Dianchi suffered due to
development of toxic cyanobacterial blooms during recent years and the fate of MCs in this aquatic
ecosystem has been studied. The concentrations of MCs ranged from 0.17 to 0.82 µg L -1 that is below
the permissible limits set by WHO. Of the three processes, i.e. absorption, photodegradation and
biodegradation, photodegradation mainly is shown to be responsible for the elimination of MCs
(Zhang et al ., 2004). In Japan cyanobacterial blooms of the species of Microcystis, i.e. M . aeruginosa ,
M . fl os - aquae , M . ichthyoblabe , M . novacekii , M . viridis and M . wesenbergii have been reported on
the basis of morphological characteristics (Komarek and Kling, 1991). Amongst these six species,
some strains of M . aeruginosa , M . ichthyoblabe and M . viridis are known to be toxic (Watanabe et al .,
1989). Further, the presence of Microcystis blooms producing MC (Tsuji et al ., 1996; Park et al ., 1998;
Matsunaga et al ., 1999) in water bodies and death of dozens of ducks (Matsunaga et al ., 1999) were
reported. Five new protease inhibitors were isolated from blooms of Lake Teganuma (Japan) that
characteristically inhibited at least one or two proteases in assays for trypsin, plasmin, chymotrypsin,
leucine aminopeptidase, carboxypeptidase A and angiotensin converting enzyme (Kodania et al .,
1999). Blooms of toxic M . aeruginosa have been represented in the water bodies from Taiwan (Lee et
al ., 1998) and Phillippines (Cuvin-Aralar et al ., 2002). The emergence of non-toxic strains of Microcystis
from the populations of MC-producing Microcystis strains KLL MG-K and KLL MB-K, isolated
from Lake Kinneret, Israel was studied. Non-toxic strains MG-J and MB-J spontaneously succeeded
as evidenced by the loss of atleast 34 kb of the mcy region governing MC synthetase. Laboratory
and fi eld experiments highlighted the advantages of the toxic strain over non-toxic counterparts
underlining the possible role of MC under natural conditions for suppressing the growth of non-
toxic strains (Schatz et al ., 2005). The recurrence of toxic blooms in Taihu Lake, China and the risk of
MC-LR exposure to human beings has been predicted on the basis of tolerable daily intake levels,
although short-term genotoxicity assays revealed negative results (Wu et al. , 2006).
Australia and New Zealand : Newly constructed shallow lakes in Queensland, Australia supported
the development blooms of Aph. ovalisporum that produces CYN. Distinctive nutrient parameters such
as ready availability of nutrients, high chloride and hardness levels triggered the bloom development
that constitutes the fi rst report from Australia. Based on 16S rRNA gene sequence Aph. ovalisporum
was shown to be identical to Aph . ovalisporum isolated from Lake Kinneret, Israel. The homology