EFFECTS OF DIFFERENT DISSOLVED ORGANIC CARBON CONCENTRATIONS AND BACTERIAL ACTIVITY ON BIODEGRADATION OF MICROCYSTIN (CYANOTOXIN).

Abstract

Microcystins degradation depends on several factors like initial concentration in water, presence of microorganisms, temperature, pH, presence of other available sources of organic carbon, and others. The aims of this study were to measure microcystin degradation under different concentrations of dissolved organic carbon (DOC), and determine the influence of bacterial community on this process. For this purpose, water from the Jacarepaguá Lagoon (Rio de Janeiro, Brazil) was diluted in deionized water in order to obtain final concentrations of DOC of 60, 43 and 28mg L-1 (water with bacteria), and final DOC concentrations of 43 and 60mg L-1 (water without bacteria). A semi-purified microcystin extract was prepared and mixed with these samples, and the concentration of microcystin and bacteria were quantified through the time. We found that DOC concentrations of 43 and 60mg L-1 with bacteria promoted total degradation of microcystin within 14 days. On the other hand, a DOC concentration of 28mg L-1 with bacteria still contained detectable microcystin after 42 days. Higher DOC concentrations promoted bacterial growth and rapid microcystin degradation. Microcystin degradation just occurred after 30 days in the absence of bacteria, illustrating their importance in this process. However, Gram negative bacteria strains isolated during the tests were not able to biodegrade microcystin.