Recent insights into physiological responses to nutrients by the cylindrospermopsin producing cyanobacterium,Cylindrospermopsis raciborskii

The harmful cyanobacterium Cylindrospermopsis raciborskii is a widespread species increasingly being recorded in freshwater systems around the world. Studies have demonstrated some key attributes of this species which may explain its global dominance. It has a high level of flexibility with respect to light and nutrients, being capable of growth under low and variable light conditions. However, it is the strategy with respect to nutrient utilization that has received more attention. Unlike many bloom forming species, the dominance of this species is not simply linked to higher nutrient loads. In fact it appears that it is more competitive when phosphorus and nitrogen availability is low and/or variable. An important component of this flexibility appears to be the result of within-population strain variability in responses to nutrients, as well as key physiological adaptations. Strain variability also appears to have an effect on the population-level cell quota of toxins, specifically cylindrospermopsins(CYNs). Field studies in Australia showed that populations had the highest proportion of toxic strains when dissolved inorganic phosphorus was added, resulting in stoichiometrically balanced nitrogen and phosphorus within the cells. These strategies are part of an arsenal of responses to environmental conditions, making it a challenging species to manage. However, our ability to improve bloom prediction will rely on a more detailed understanding of the complex physiology and ecology of this species.

The morphological and molecular detection for the presence of toxic Cylindrospermopsis(Nostocales, Cyanobacteria) in Beijing city, China

Cylindrospermopsis raciborskii and its highly similar relatives Raphidiopsis species have been recognized as globally invasive and expansive filamentous cyanobacteria causing water blooms. Reports on C. raciborsMi/Raphidiopsis species and their harmful metabolites such as hepatotoxic cylindrospermopsins （CYNs） in Chinese waters have been increasing, but mostly restricted to the southern regions of China. To further explore the existence and distribution of C. raciborskii in China, six water samples from Beijing city were morphologically and molecularly examined. Five samples of the six were shown to have Cylindrospermopsis filaments with straight and spiral morphotypes. PCR detection targeting on Cylindrospermopsis/Raphidiopsis specific 16S rRNA gene region also showed the positive amplification, and such amplifications were confirmed by sequencing and phylogenetic analysis. As well, three of the five Cylindrospermopsis containing samples were shown to have cyrJ--a gene of CYN synthesis gene duster. The results represented the presence of toxic Cylindrospermopsis at the most northern line in China so far, indicating rapid expansion of this harmful invasive cyanobacterium. It is strongly suggested that the monitoring on C. raciborskii/Raphidiopsis species and their production of cylindrospermopsin should be emphasized in Beijing and even more northem parts of China.

The effect of cylindrospermopsin on the bacterioplankton community:a microcosm experiment on water from Dishui Lake,Shanghai,China

Eutrophication and climate warming have intensified the global expansion of invasive cyanobacteria such as Cylindrospermopsis spp.and Chrysosporum spp.Cylindrospermopsin(CYN)produced by species of the latter two genera may harm phytoplankton,zooplankton,and fishes.However,effects of CYN on the bacterioplankton community have not been studied.Based on high-throughput sequencing,we explored the effect of CYN on the structure and function of the bacterioplankton community by adding pure CYN to in-situ water collected from a brackish coastal shallow lake:Dishui Lake,China.We found that most bacterioplankton taxa had a certain tolerance potential to CYN,but that high concentrations of CYN(40μg/L)caused a significant decrease in microbial abundance and functional groups.Of the dominant phyla,Actinobacteria had the strongest tolerance to CYN.Network analysis indicated that CYN caused shifts in the community structure of the bacterioplankton,reducing community stability and structural complexity.High CYN concentrations also reduced the correlation between the different bacterioplankton groups,and the abundances of some bacterial taxa associated with the denitrification function and the process of carbon transfer in the microbial food web were inhibited.Our study provide s new insight into the response of the bacterioplankton communities to harmful algal toxins produced by cyanobacteria.

First TaqMan Assay to Identify and Quantify the Cylindrospermopsin-Producing Cyanobacterium <i>Aphanizomenon ovalisporum</i>in Water

Cylindrospermopsin (CYN) is an alkaloid that causes hepatotoxicity, neurotoxicity and general cytotoxicity in vertebrates. It is currently gaining widespread attention after its reported appearance in water bodies around the world. A. ovalisporum is capable of CYN-production and can form toxic blooms when favorable environmental conditions are available. We have developed for the first time a two-step qPCR assay using Taqman probes to detect and quantify potential CYN-producing A. ovalisporum in water samples. The assay was sensitive enough to discriminate between CYN-producing and non-CYN-producing A. ovalisporum in a mixed background, and discriminate between A. ovalisporum and other nostocales as C. raciborskii and A. bergii. The detection limit of the assay falls in the log linear range of 102 and 105 gene copies per reaction and is thus within the sensitivity range of previously published assays for the detection of other toxic cyanobacteria species. Our assay allows for the first time to quickly assess water quality for the presence of potentially CYN-producing A. ovalisporum and can be easily used for the purposes of monitoring water bodies.

Alteration of Cylindrospermopsin Content of <i>Aphanizomenon ovalisporum</i>(Cyanobacteria, Nostocales) due to Step-Down from Combined Nitrogen to Dinitrogen

In this study we show that cylindrospermopsin (a cyanotoxin) content of filaments of Aphanizomenon ovalisporum ILC164 depended on growth on combined nitrogen or nitrogen fixation. Our results also demonstrated that the shift down of cyanobacterial filaments from combined nitrogen to dinitrogen fixing condition resulted in a significant decrease of cylindrospermopsin pool size which resumed a growth rate dependent manner as the heterocyst and nitrogenase formation appeared. The current study indicated that alteration of nitrogen metabolism of Aphanizomenon ovalisporum (Forti) induced changes in cyanotoxin (cylindrospermopsin) metabolism. In addition, this is the first report that isolated heterocysts, the differentiated anaerobic cells for nitrogen fixation of cyanobacteria, did not contain cylindrospermopsin.

Revealing Toxin Signatures in Cyanobacteria: Report of Genes Involved in Cylindrospermopsin Synthesis from Saxitoxin-Producing <i>Cylindrospermopsis raciborskii</i>

Cyanotoxins are distinctive molecules in Cyanobacteria whose evolutionary origin, radiation and ecological role are still controversial. The cyanobacterium Cylindrospermopsis raciborskii is alternately capable of producing two types of potent toxins, cylindrospermopsin (CYN) or saxitoxin and analogues (SAX). It has been proposed that this species spread to all continents early in its evolutionary history and biogeographical differences in toxin production are found between populations. Most reports indicate that American strains are able to produce SAX but not CYN, while Australian strains are described to produce CYN but not SAX. Here we describe the presence of three genes belonging to the cylindrospermopsin cluster (cyr), cyrA, cyrB and cyrC, in two SAX producing South American C. raciborskii strains, MVCC14 and MVCC19, which due to their differences in morphology, growth preferences, SAX production and genetic context are defined as different ecotypes. No CYN production was detected in either strain (by ELISA) after growth under nitrogen replete or nitrogen-free nutrient conditions. Phylogenetic analyses of cyrA, cyrB and cyrC partial sequences from both strains showed high similarity (>99%) with CYN genes belonging to C. raciborskii strains from Australia and Germany and to Aphanizomenon strains. This is the first report of the presence of cyr genes in strains known to produce only SAX.