Molecular Verification of Bloom-forming Aphanizomenon flos-aquae and Their Secondary Metabolites in the Nakdong River

Abstract

Aphanizomenon spp. have formed harmful cyanobacterial blooms in the Nakdong River during spring, autumn, and now in winter, and the expansion of blooming period and area, associated with the global warming is predicted. The genus Aphanizomenon has been described to produce harmful secondary metabolites such as off-flavors and cyanotoxins. Therefore, the production of harmful secondary metabolites from the Aphanizomenon blooms in the Nakdong River needs to be monitored to minimize the risk to both water quality and public health. Here, we sampled the cyanobacterial blooms in the Nakdong River and isolated ten Aphanizomenon strains, morphologically classified as Aphanizomenon flos-aquae Ralfs ex Bornet et Flahault 1888. Phylogenetic analysis using 16S rRNA and internal transcribed spacer (ITS) region nucleotide sequences confirmed this classification. We further verified the harmful secondary metabolites-producing potential of A. flos-aquae isolates and water samples containing cyanobacterial blooms using PCR with specific primer sets for genes involved in biosynthesis of off-flavor metabolites (geosmin) and toxins (microcystins, saxitoxins and cylindrospermopsins). It was confirmed that these metabolite biosynthesis genes were not identified in all isolates and water samples containing only Aphanizomenon spp. Thus, it is likely that there is a low potential for the production of off-flavor metabolites and cyanotoxins in Aphanizomenon blooms in the Nakdong River.

Detection of Cyanotoxin-Producing Genes in a Eutrophic Reservoir (Billings Reservoir, São Paulo, Brazil)

“…To date, few studies have evaluated the presence of several genes of clusters responsible for biosynthesis of microcystin, cylindrospermopsin and saxitoxin in environmental samples [11,[27][28][29][30][31][32][33][34][35], when compared to the majority of studies in which only one gene is used. Of these, five [28,30,[33][34][35] reported results similar to those obtained in this work, i.e., differential amplification between genes responsible for biosynthesis of a cyanotoxin.…”

“…Cyanotoxins are large groups of secondary metabolites which are toxic to most eukaryotic organisms and can be classified according to their mechanism of action: neurotoxic (anatoxin-a and analogues, saxitoxin and analogues), hepatotoxic (microcystins and nodularins), dermatotoxic (lipopolysaccharides) and cytotoxic (cylindrospermopsins) [6][7][8]. Some species and genera, such as Microcystis aeruginosa, Raphidiopsis raciborskii (Woloszynska) Aguilera, Berrendero Gómez, Kastovsky, Echenique and Salerno (basionym Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju) [9], Planktothrix and Dolichospermum have been numerously reported to produce toxins [7,[10][11][12].…”

“…Nevertheless, there is no consensus on which gene would be most appropriate to infer the presence of toxins [18,20,21,25,26]. Despite the full description of gene clusters responsible for the production of toxins, studies evaluating more than one gene are still not many when compared to studies evaluating one gene alone [11,[27][28][29][30][31][32][33][34][35].…”

Characterization of Distinct CyanoHABs-Related Modules in Microbial Recurrent Association Network

“…Aphanizomenon is usually reported in the summer, before and after Microcystis blooms, in the Nakdong River. However, serious blooms of Aphanizomenon have been observed in winter in the Nakdong River since 2015 (Park et al, 2018). We found that the December nCCCs were mainly influenced by the relative abundance of Aphanizomenon and by discharge (Figure 3).…”

Comparative growth characteristics and interspecific competitive interaction of two cyanobacteria, Phormidium autumnale and Nostoc sp.

“…The most predominant bloom‐forming cyanobacterial species in rivers were Microcystis , Anabaena , Oscillatoria , and Phormidium (Hong et al., 2018; Hur et al., 2013; Lee et al., 2018). Several studies examined how different environmental conditions affect the cyanobacterial composition and the production of harmful secondary metabolites in rivers (Kim et al., 2017; Lee et al., 2018; Park et al., 2018; Srivastava et al., 2015). Shifts in the population dynamics and toxin production were often reported due to nutrient and physical factors (Srivastava et al., 2015).…”