Effect of Physicochemical and Biological Parameters on the Occurrence of Microcystin-Lr and Their Destruction by Microbes

Abstract

Attached

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.