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.
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.
J Venom Anim Toxins Incl Trop Dis. 2015 Feb 24;21:4. doi: 10.1186/s40409-015-0001-3. eCollection 2015.
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.
[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.
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.
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.
有毒蓝藻水华在巴西南部的帕托斯湖反复出现。在蓝藻毒素中，[D-Leu(1)] 微囊藻-LR 是主要的变体，其自然循环涉及水和沉积物两个部分。本研究旨在从沉积物中分离出一种能够以 [D-Leu(1)] 微囊藻-LR 为唯一碳源生长的细菌菌株。在巴西南里奥格兰德州里奥格兰德市的海洋博物馆附近（P1）和南里奥格兰德州圣洛伦索市的圣洛伦索海滩（P2）两个不同的水域采集了水和沉积物样本。[D-Leu(1)] 微囊藻-LR 从铜绿微囊藻株 RST9501 的分批培养物中分离和纯化。采集了里奥格兰德和南里奥格兰德州的水和沉积物样本。将样本中的细菌在仅含有 [D-Leu(1)] 微囊藻-LR 的烧瓶中培养。这种菌株被命名为 DMSX，它是在含有 8 g L(-1) 葡萄糖的 MSM 琼脂上，根据微囊藻毒素的生长情况进行进一步纯化。通过使用 ELISA 免疫分析法测定微囊藻毒素来获得微囊藻浓度，而通过荧光显微镜测定细菌计数。通过 DNA 技术鉴定了假单胞菌属。
尽管从样品中分离出了几种细菌菌株，但只有一种，即 DMSX，能够以 [D-Leu(1)] 微囊藻-LR 为唯一碳源生长。从 DMSX 菌株的 16S rRNA 基因的系统发育分析将该生物归类为铜绿假单胞菌。用 [D-Leu(1)] 微囊藻-LR 孵育的 DMSX 菌株将毒素的量从 1 μg.L(-1)降低到<0.05 μg.L(-1)。此外，在孵育过程中，细菌计数从 71×10(5)个细菌.mL(-1)增加到 117×10(5)个细菌.mL(-1)。
从沉积物中分离出的细菌用于去除有毒化合物的技术应用是可行的。研究表明，沉积物作为能够降解蓝藻毒素的细菌的来源发挥着重要作用。这是巴西首例报道的能够降解 [D-Leu(1)] 微囊藻-LR 的细菌，[D-Leu(1)] 微囊藻-LR 是巴西淡水湖中最常见的微囊藻毒素变体。
