Microcystin Biodegradation Study Using a Lagoa Dos Patos Estuary Sediment in Southern of Brasil and a Comparative Analysis of Biodegradation with Isolated Bacteria

Gilmar A F Lemes,João S Yunes

doi:10.12691/ijebb-5-2-2

Abstract

In the Lagoa dos Patos Estuary, southern Brazil, toxic blooms of cyanobacteria have been recorded for many years. Among the species of cyanobacteria that occur in the estuary Microcystis aeruginosa produces the toxin [D-Leu1] microcystin-LR, one of the most toxic known variants. The strain Microcystis aeruginosa RST9501 was cultivated in Cyanobacteria and Phycotoxins Lab of the Oceanography Institute of the Federal University of Rio Grande - FURG and it was used for toxin extraction and purification. Sediment samples were collected from the estuary and used in the toxin degradation experiments. The decrease of toxin concentration was checked by HPLC and the results were compared with other available data. This study revealed the decreased of toxin [D-Leu1] microcystin-LR concentration of 5µg.mL-1 after six days, and also describes a comparative analysis of the biodegradation by the sediment and with a bacterium isolated from the collected sediment samples. It was suggested that the reduction in toxin concentration is mainly due the biodegradation by the bacterial community of Lagoa dos Patos Estuary present in the sediment. This confirms the potential of this technique as a complementary tool for biotechnological processes to remove toxins in water. It was also carried out a comparative analysis of the biodegradation of the toxin with sediment and biodegradation with an isolated bacteria from this sediment.

Highlights

The occurrence of toxic cyanobacterial blooms has been reported for more than 20 years in the Lagoa dos Patos Estuary [21,36,38]
This study aims to identify the use of sediment from the Lagoa dos Patos Estuary as a substrate with potential for the biodegradation of toxin [D-Leu1] microcystin-LR and as a source of bacteria carrying enzymes capable of biodegrading this compound, as well as to compare the process of biodegradation with the sediment and from a bacterial strain isolated from this sediment
Sediment samples from Lagoa dos Patos Estuary were collected and their potential to induce the reduction of the concentration of [D-Leu1] microcystin-LR toxin was evaluated

Summary

Introduction

The occurrence of toxic cyanobacterial blooms has been reported for more than 20 years in the Lagoa dos Patos Estuary [21,36,38]. The predominant species of cyanobacteria in the estuary, Microcystis aeruginosa, is known for producing hepatotoxin [D-Leu1] microcystinLR ([D-Leu1] MC-LR) [22,23], which represents 90% of all toxins produced intracellularly. The hepatotoxicity of this variant has already been reported through animals and enzymatic bioassays data. More than 70 structural variants have been described in the literature. These toxins promote tumors and are involved in acute and chronic health problems in humans and animals

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