title: Biodegradation of [D-Leu(1)] microcystin-LR by a bacterium isolated from sediment of Patos Lagoon estuary, Brazil.
abstract: BACKGROUND
  Toxic cyanobacterial blooms are recurrent in Patos Lagoon, in southern Brazil. Among cyanotoxins, [D-Leu(1)] microcystin-LR is the predominant variant whose natural cycle involves water and sediment compartments. This study aimed to identify and isolate from sediment a bacterial strain capable of growing on [D-Leu(1)] microcystin-LR. Sediment and water samples were collected at two distinct aquatic spots: close to the Oceanographic Museum (P1), in Rio Grande City, and on São Lourenço Beach (P2), in São Lourenço do Sul City, southern Brazil.
  
  
  METHODS
  [D-Leu(1)] microcystin-LR was isolated and purified from batch cultures of Microcystis aeruginosa strain RST9501. Samples of water and sediment from Rio Grande and São Lourenço do Sul were collected. Bacteria from the samples were allowed to grow in flasks containing solely [D-Leu(1)] microcystin-LR. This strain named DMSX was isolated on agar MSM with 8 g L(-1) glucose and further purified on a cyanotoxin basis growth. Microcystin concentration was obtained by using the ELISA immunoassay for microcystins whereas bacterial count was performed by epifluorescence microscopy. The genus Pseudomonas was identified by DNA techniques.
  
  
  RESULTS
  Although several bacterial strains were isolated from the samples, only one, DMXS, was capable of growing on [D-Leu(1)] microcystin-LR. The phylogenetic analysis of the 16S rRNA gene from DMXS strain classified the organism as Pseudomonas aeruginosa. DMXS strain incubated with [D-Leu(1)] microcystin-LR lowered the amount of toxin from 1 μg.L(-1) to < 0.05 μg.L(-1). Besides, an increase in the bacterial count-from 71 × 10(5) bacteria.mL(-1) to 117 × 10(5) bacteria.mL(-1)-was observed along the incubation.
  
  
  CONCLUSIONS
  The use of bacteria isolated from sediment for technological applications to remove toxic compounds is viable. Studies have shown that sediment plays an important role as a source of bacteria capable of degrading cyanobacterial toxins. This is the first Brazilian report on a bacterium-of the genus Pseudomonas-that can degrade [D-Leu(1)] microcystin-LR, the most frequent microcystin variant in Brazilian freshwaters.
authors.affiliation: Laboratório de Cianobactérias e Ficotoxinas, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália, km 8, Campus Carreiros, Caixa postal 474, Rio Grande, RS CEP 96203-000 Brazil.
authors.forename: Gilmar Af
authors.initials: GA
authors.lastname: Lemes
authors.affiliation: Laboratory of Genomics and Molecular Biology, School of Biosciences, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Porto Alegre, Rio Grande do Sul State Brazil.
authors.forename: Luiza W
authors.initials: LW
authors.lastname: Kist
authors.affiliation: Laboratory of Genomics and Molecular Biology, School of Biosciences, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Porto Alegre, Rio Grande do Sul State Brazil ; National Institute of Science and Technology for Translational Medicine, Porto Alegre, Rio Grande do Sul State Brazil.
authors.forename: Mauricio R
authors.initials: MR
authors.lastname: Bogo
authors.affiliation: Laboratório de Cianobactérias e Ficotoxinas, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália, km 8, Campus Carreiros, Caixa postal 474, Rio Grande, RS CEP 96203-000 Brazil.
authors.forename: João S
authors.initials: JS
authors.lastname: Yunes
keywords: Biodegradation; Brazil; Estuary; Microcystin; Patos Lagoon; Sediment