CYANOBACTERIAL TOXINS - Cyanobacteria - page 557

mcyD gene, the number of toxic cell numbers of Microcystis were determined to be in the range of
4 x 10 8 to 2 x 10 3 cells L -1 . By using sequence analysis of mcyA gene fragments, the occurrence of toxic
Microcystis and Planktothrix was documented in the previously undetected localities in the western
basin of Lake Erie (Rinta-Kanto and Wilhelm, 2006).
In as many as 27 states of USA, HABs have been reported (Codd et al ., 2005). Based on studies on
the occurrence of toxic cyanobacterial blooms in surface drinking waters in the state of Florida, the
incidence of primary hepatocellular carcinoma was diagnosed in patients in between 1981 and 1998
(Fleming et al ., 2002). Lyngbya dominated blooms in a North Louisiana reservoir were investigated
to know their potential toxicity to the survival, reproduction and behaviour of Daphnia magna and
Pimephales promealis . Risk evaluation experiments recommended the application of a herbicide
whose active ingredient is copper for effective control of Lyngbya blooms (Mastin et al ., 2002).
Physicochemical data from 241 lakes in Missouri, Iowa, northeastern Kansas and southern Minnesota
revealed the total phosphorus and total nitrogen to be in the range of 2-995 and 90-15870 µg L -1 ,
respectively. The MC content of lake waters increased with increased latitutes from undetectable
to 4500 ng L -1 . For effective lake management and minimization of human health risks, the authors
suggested that the empirical relationships between environmental variables and MC values have to
be taken into consideration (Graham et al ., 2004). A study on the genetic variation within and among
populations of M . aeruginosa in southern Michigan Lakes revealed that 53 of the 67 isolates were
genetically distinct as determined on the basis of mcyA gene marker. Besides studying the various
limnological characteristics of these lakes, a relationship between survivorship of the isolate and
composition of the medium has been established. For example, a low rate of survival of isolates
from oligotrophic lakes was noted when cultured in nutrient-rich algal medium. Additionally, four
strains of M . aeruginosa from three freshwater lakes of North America, Africa and Europe (isolated
and maintained in pure cultures) were genetically analyzed and compared with those of natural
populations. These four strains are not only related to each other but also exhibited similarity to most
of the strains of Bear Lake and Spring Lake suggesting that a similarity of nutrient levels in these
bodies and nutrient medium employed (Wilson et al ., 2005). Out of a total 182 lakes and reservoirs
of Indiana surveyed for HABs, 19 of them showed detectable growth of C . raciborskii during late
summer months of August and September of 2002 and 2003. Both straight and curled morphotypes
have been detected. The bloom has been widely represented in 35% of the impoundments sampled
(n=40) than in natural lakes. Though bottom temperatures of shallow lakes reached 22-23.5ºC, the
mean tempearure in the deepest waters of lakes in which C . raciborskii was detected was 18.2ºC
and with surface temperatures of 26.5ºC. High epilimnetic phosphorus content is characteristic of
these lakes (Jones ans Sauter, 2005). Sheldon Lake of Colorodo, a public recreational focal point,
supported the development of toxic Microcystis blooms as confi rmed by the use of molecular markers
of the mcy gene cluster (Oberholster et al ., 2006). Water samples (247) collected from the Salton
Sea (a saline endorheic rift lake that is largest in California), dominated by Synechococcus sp. and
benthic fi lamentous Oscillatoria sp., yielded the presence of MCs. Pure cultures of both the dominant
organisms produced MC-LR and MC-YR (Carmichael et al ., 2006).
Extensive blooms of Anabaenopsis have been reported in Bedetti Lake, Argentina (Fig. 24). Brazil
attracted the attention of the whole world in a glaring instance of the death of 60 patients of a kidney
dialysis centre due to supply of drinking water from a lake that suffered from the blooms of Anabaena
and Microcystis (Jochimsen et al ., 1998; Pouria et al ., 1998). Toxic cyanobacterial blooms have been
recorded from various habitats of Brazil such as estuaries (Yunes et al ., 1996), lagoons (Azevedo et al .,
1994; Azevedo 1996; Porfi rio et al ., 1999; Lagos et al ., 1999; Magalhaes et al ., 2001) and reservoirs (Bouvy
et al ., 1999; Chelleppa et al ., 2000; Costa et al ., 2001; Molica et al ., 2002). Lakes in the state of Parana' of