Cyanobacteria are photosynthetic oxygenic microorganisms that belong to the Bacteria domain, and possess cosmopolitan distribution on Earth. Some species produce potent toxins (e.g., microcystins, saxitoxins, cylindrospermopsins, anatoxin-a, anatoxin-a(S), among others) elaborated by an enzymatic mechanism that is parallel to the protein synthesis. In biological terms, saxitoxins (STX) are neurotoxins that prevent the normal propagation of nerve impulses to muscles, causing paralysis and death by respiratory arrest and choking. Its production has been described for some filamentous cyanobacteria of different genera, such as Cylindrospermopsis raciborskii, a planktonic species commonly found in Brazilian water bodies used for public supply. The putative sxt gene cluster responsible for the STX biosynthesis was obtained by the "PCR walking" technique from the genome of C. raciborskii strain T3, which was isolated from Billings reservoir (SP). However, information about cyanotoxins produced by benthic cyanobacteria is scarce despite several world records of deaths and animal poisonings. Recently, in 2015, the potential for STX production in benthic cyanobacterial strains of the genus Geitlerinema (G. amphibium and G. lermmermannii) isolated from the Brazilian northeastern region was reported for the first time, taking into account the sxtA gene detection, one of those involved in its biosynthesis. Cyanobacteria cultivation is extremely hard in laboratory conditions, and there are few published studies using Brazilian strains. This proposal aims to investigate the potential for STX production in strains of Cylindrospermopsis (plancktonic) and Geitlerinema (benthic) from different Brazilian water bodies, especially located in the semiarid region. Genomic DNA will be extracted and used for PCR amplification of the sxtA gene. Amplicons will be sequenced and the sequences generated will be used to determine the evolutionary distances based on phylogenetic trees. The outcomes of this study might promote the future construction of biochips for detecting the toxicological potential of cyanobacteria in specific aquatic environments.
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