Cylindrospermopsin production and release by the potentially invasive cyanobacterium Aphanizomenon ovalisporum under temperature and light gradients

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dPlanktonic Nostocales cyanobacteria represent a challenge for microbiological research because of the wide range of cyanotoxins that they synthesize and their invasive behavior, which is presumably enhanced by global warming. To gain insight into the phylogeography of potentially toxic Nostocales from Mediterranean Europe, 31 strains of Anabaena (Anabaena crassa, A. lemmermannii, A. mendotae, and A. planctonica), Aphanizomenon (Aphanizomenon gracile, A. ovalisporum), and Cylindrospermopsis raciborskii were isolated from 14 freshwater bodies in Spain and polyphasically analyzed for their phylogeography, cyanotoxin production, and the presence of cyanotoxin biosynthesis genes. The potent cytotoxin cylindrospermopsin (CYN) was produced by all 6 Aphanizomenon ovalisporum strains at high levels (5.7 to 9.1 g CYN mg ؊1 [dry weight]) with low variation between strains (1.5 to 3.9-fold) and a marked extracellular release (19 to 41% dissolved CYN) during exponential growth. Paralytic shellfish poisoning (PSP) neurotoxins (saxitoxin, neosaxitoxin, and decarbamoylsaxitoxin) were detected in 2 Aphanizomenon gracile strains, both containing the sxtA gene. This gene was also amplified in non-PSP toxin-producing Aphanizomenon gracile and Aphanizomenon ovalisporum. Phylogenetic analyses supported the species identification and confirmed the high similarity of Spanish Anabaena and Aphanizomenon strains with other European strains. In contrast, Cylindrospermopsis raciborskii from Spain grouped together with American strains and was clearly separate from the rest of the European strains, raising questions about the current assumptions of the phylogeography and spreading routes of C. raciborskii. The present study confirms that the nostocalean genus Aphanizomenon is a major source of CYN and PSP toxins in Europe and demonstrates the presence of the sxtA gene in CYN-producing Aphanizomenon ovalisporum.

Section: Cyanotoxin Analysis (I) Lc-ms/ms and Hplc-pdamentioning

confidence: 99%

Section: Cyanotoxin Analysis (I) Lc-ms/ms and Hplc-pdamentioning

confidence: 99%

Section: Cyanotoxin Analysis (I) Lc-ms/ms and Hplc-pdamentioning

confidence: 99%

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Phylogeography of Cylindrospermopsin and Paralytic Shellfish Toxin-Producing Nostocales Cyanobacteria from Mediterranean Europe (Spain)

Cirés

Wörmer

Ballot

et al. 2014

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“…These studies, therefore, have provided evidence that CYN pool size may be linked to one or more environmental drivers. However, whether cellular pool size is constitutive or is affected by changes in cell physiological status is unclear.Several studies have been carried out to investigate the effects of environmental factors such as light intensity, temperature, nitrogen and phosphate availability, and culture age on CYN production by C. raciborskii and other CYN-producing cyanobacteria (8,(14)(15)(16)(17)(18)(19)(20)(21). On the other hand, while the effects of elevated CO 2 on production of other cyanotoxins (such as microcystins and saxitoxins) by other cyanobacteria and dinoflagellates have been studied (22, 23), the effect of CO 2 on CYN pool size by C. raciborskii has not.…”

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confidence: 99%

Constitutive Cylindrospermopsin Pool Size in Cylindrospermopsis raciborskii under Different Light and CO ₂ Partial Pressure Conditions

Pierangelini

Sinha

Willis

et al. 2015

d Cylindrospermopsin (CYN) and 7-deoxy-cylindrospermopsin (dCYN) are potent hepatotoxic alkaloids produced by numerous species of cyanobacteria, including the freshwater Cylindrospermopsis raciborskii. C. raciborskii is an invasive cyanobacterium, and the study of how environmental parameters drive CYN production has received significant interest from water managers and health authorities. Light and CO 2 affect cell growth and physiology in photoautotrophs, and these are potential regulators of cyanotoxin biosynthesis. In this study, we investigated how light and CO 2 affect CYN and dCYN pool size as well as the expression of the key genes, cyrA and cyrK, involved in CYN biosynthesis in a toxic C. raciborskii strain. For cells growing at different light intensities (10 and 100 mol photons m ؊2 s ؊1 ), we observed that the rate of CYN pool size production ( CYN ) was coupled to the cell division rate ( c ) during batch culture. This indicated that CYN pool size under our experimental conditions is constant and cell quotas of CYN (Q CYN ) and dCYN (Q dCYN ) are fixed. Moreover, a lack of correlation between expression of cyrA and total CYN cell quotas (Q CYNs ) suggests that the CYN biosynthesis is regulated posttranscriptionally. Under elevated CO 2 (1,300 ppm), we observed minor effects on Q CYN and no effects on expression of cyrA and cyrK. We conclude that the CYN pool size is constitutive and not affected by light and CO 2 conditions. Thus, C. raciborskii bloom toxicity is determined by the absolute abundance of C. raciborskii cells within the water column and the relative abundance of toxic and nontoxic strains. C ylindrospermopsins (CYNs) are a group of related toxic polyketide-derived hepatotoxic alkaloids which are produced by several species of cyanobacteria from genera including Aphanizomenon, Oscillatoria, Anabaena, Raphidiopsis, and Cylindrospermopsis (1). The cyanobacterium Cylindrospermopsis raciborskii (Wołoszyń ska, Nostocales) Seenaya et Subba Raju has received particular attention in recent decades due to its ability to form harmful algal blooms (HAB), combined with its invasive capacity and recent latitudinal expansion (2-4).Three CYNs are known to be produced by C. raciborskii in Australia (5), namely, cylindrospermopsin (CYN), 7-epi-cylindrospermopsin (7-epi-CYN), and 7-deoxy-cylindrospermopsin (dCYN). Each is known to be produced in differing amounts by different strains found in Australia, New Zealand, South Africa, and Thailand (6, 7). All CYNs are produced intracellularly and are thought to be released into the surrounding water body during cell lysis (8). In Australian strains of C. raciborskii, 7-epi-CYN is a minor component (usually less than 5% of the total CYNs), and it is not further considered in this study. CYNs are sensitive to sunlight but rather resistant to temperature, artificial light, and pH changes (9). Because of these natural properties, CYNs can accumulate in a water body, presenting serious environmental and human health risks (10). Thus, it is imperative to understand...

“…However, the protein-DNA interaction has not been verified in other CYN-producing species. The effects of temperature, light, nitrogen, phosphate, and sulfate on CYN production are inconclusive because of uncertainties in strain dependence, the release of CYNs, heterocyst formation, and combined effects of multiple factors in different experimental conditions (43)(44)(45)(46)(47)(48)(49)(50)(51). Davis et al (51) highlighted the effects of the genetic diversity of CYN producers on the concentration and composition of CYNs in aquatic ecosystems.…”

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confidence: 99%

Sporadic Distribution and Distinctive Variations of Cylindrospermopsin Genes in Cyanobacterial Strains and Environmental Samples from Chinese Freshwater Bodies

Jiang

Xiao

et al. 2014

e Increasing reports of cylindrospermopsins (CYNs) in freshwater ecosystems have promoted the demand for identifying all of the potential CYN-producing cyanobacterial species. The present study explored the phylogenetic distribution and evolution of cyr genes in cyanobacterial strains and water samples from China. Four Cylindrospermopsis strains and two Raphidiopsis strains were confirmed to produce CYNs. Mutant cyrI and cyrK genes were observed in these strains. Cloned cyr gene sequences from eight water bodies were clustered with cyr genes from Cylindrospermopsis and Raphidiopsis (C/R group) in the phylogenetic trees with high similarities (99%). Four cyrI sequence types and three cyrJ sequence types were observed to have different sequence insertions and repeats. Phylogenetic analysis of the rpoC1 sequences of the C/R group revealed four conserved clades, namely, clade I, clade II, clade III, and clade V. High sequence similarities (>97%) in each clade and a divergent clade IV were observed. Therefore, CYN producers were sporadically distributed in congeneric and paraphyletic C/R group species in Chinese freshwater ecosystems. In the evolution of cyr genes, intragenomic translocations and intergenomic transfer between local Cylindrospermopsis and Raphidiopsis were emphasized and probably mediated by transposases. This research confirms the existence of CYN-producing Cylindrospermopsis in China and reveals the distinctive variations of cyr genes.