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M icrocystin-LR (M C-LR) is one o f the most toxic cyanobacterial secondary
metabolites present in Sri Lankan water bodies. MC-LR intoxication can cause serious health
issues to humans and other organisms through the use o f MC-LR contaminated water. MC-LR
is produced within the cells o f different genera o f freshwater cyanobacteria: M icrocystis,
Anabaena, Oscillatoria (Planktothrh), Nostoc, and Anabaenopsis. However, heterotrophic
bacteria in freshwater can degrade MC-LR into non-harmful products under optimal
environmental conditions. The present study focuses on the effect o f physicochem ical and
biological parameters o f water on occurrence o f MC-LR and their removal by bacteria.
The present study was carried out from Ist September 2011 to 3 Ist August 2014 in
som e selected water bodies o f Sri Lanka. Water samples were collected from five locations of
each water body. Water temperature, pH, electrical conductivity (EC), dissolved oxygen (DO),
total phosphate (TP), nitrate nitrogen (NO.T-N), chlorophyll-a, cyanobacterial cell density and
total MC-LR were analyzed. Enrichment studies were carried out to isolate MC-LR degrading
bacteria and BIOLOG MT2 plate method was employed in screening o f the efficiency o f MCLR degraders. Pearson Correlation Coefficient (PCC) analysis and Principle Component
Analysis (PCA) were used to analyze data.
PCC calculated between physicochemical parameters, cyanobacterial cell density and
MC - LR levels o f water bodies found that p -values for water temperature (0.009). pH (0.002),
TP (0.001), NOT-N (0.01) and cyanobacterial cell density (0.001) were positively correlated
with MC-LR concentration in water. However, cholorophyll-a concentration did not show a
correlation with MC-LR concentration as chlorophyll-a is a pigment from green algae as well.
Moreover, the PCA analysis found that the water bodies studied were clustered in three
different ways: A ,B and C. Cluster A included water bodies with low values for all measured
parameters including MC-LR. whereas clusters B and C included water bodies with high
values for all measured parameters and MC-LR. Cluster C was a sub set o f cluster B.
However, water bodies in cluster A did not show the presence o f efficient MC-LR degraders,
while water bodies belonging to cluster B and C had MC-LR degrading bacteria in their
environment. The most efficient MC-LR degrader was detected in cluster C. Thus, unlike
water bodies in cluster A. conditions prevailing in water bodies in cluster B and C favours
MC-LR production by cyanoabcteria and heterotrophic bacterial metabolism o f MC-LR.
Therefore, it is clear that the analysis o f physicochemical and biological parameters in water
will be a useful monitoring tool to predict the presence o f MC-LR in water and their
destruction by microbes.
