Next-generation DNA sequencing technology was applied
to generate molecular data from semiarid reservoirs during
well-defined seasons. Target sequences of 16S-23S rRNA ITS
and cpcBA-IGS were used to reveal the taxonomic groups of
cyanobacteria present in the samples, and genes coding for
cyanotoxins such as microcystins (mcyE), saxitoxins (sxtA),
and cylindrospermopsins (cyrJ) were investigated. The presence
of saxitoxins in the environmental samples was evaluated
using ELISA kit. Taxonomic analyses of high-throughput
DNA sequencing data showed the dominance of the genus
Microcystis in Mundaú reservoir. Furthermore, it was the
most abundant genus in the dry season in Ingazeira reservoir.
In the rainy season, 16S-23S rRNA ITS analysis revealed that
Cylindrospermopsis raciborskii comprised 46.8% of the cyanobacterial
community in Ingazeira reservoir, while the cpcBAIGS
region revealed that C. raciborskii (31.8%) was the most
abundant taxon followed by Sphaerospermopsis aphanizomenoides
(17.3%) and Planktothrix zahidii (16.6%). Despite
the presence of other potential toxin-producing genera, the
detected sxtA gene belonged to C. raciborskii, while the mcyE
gene belonged to Microcystis in both reservoirs. The detected
mcyE gene had good correlation with MC content, while the
amplification of the sxtA gene was related to the presence of
STX. The cyrJ gene was not detected in these samples. Using
DNA analyses, our results showed that the cyanobacterial
composition of Mundaú reservoir was similar in successive
dry seasons, and it varied between seasons in Ingazeira reservoir.
In addition, our data suggest that some biases of analysis
influenced the cyanobacterial communities seen in
the NGS output of Ingazeira reservoir.