Toxicity Overrides Morphology on Cylindrospermopsis raciborskii Grazing Resistance to the Calanoid Copepod Eudiaptomus gracilis.

Toxicity and morphology may function as defense mechanisms of bloom-forming cyanobacteria against zooplankton grazing. Yet, the relative importance of each of these factors and their plasticity remains poorly known. We tested the effects of chemical and morphological traits of the bloom-forming cyanobacterium Cylindrospermopsis raciborskii on the feeding response of the selective feeder Eudiaptomus gracilis (Calanoida, Copepoda), using a saxitoxin-producing strain (STX+) and a non-saxitoxin (STX-)-producing strain as food. From these two chemotypes, we established cultures of three different morphotypes that differed in filament length (short, medium, and long) by incubating the strains at 17, 25, and 32 °C. We hypothesized that the inhibitory effects of saxitoxins determine the avoidance of C. raciborskii, and that morphology would only become relevant in the absence of saxitoxins. Temperature affected two traits: higher temperature resulted in significantly shorter filaments in both strains and led to much higher toxin contents in the STX+ strain (1.7 µg eq STX L(-1) at 17 °C, 7.9 µg eq STX L(-1) at 25 °C, and 25.1 µg eq STX L(-1) at 32 °C). Copepods strongly reduced the ingestion of the STX+ strain in comparison with STX- cultures, regardless of filament length. Conversely, consumption of shorter filaments was significantly higher in the STX- strain. The great plasticity of morphological and chemical traits of C. raciborskii and their resultant contrasting effects on the feeding behavior of zooplankton might explain the success of this cyanobacterium in a variety of aquatic environments.

Elevated CO2 causes changes in the photosynthetic apparatus of a toxic cyanobacterium, Cylindrospermopsis raciborskii.

We studied the physiological acclimation of growth, photosynthesis and CO2-concentrating mechanism (CCM) in Cylindrospermopsis raciborskii exposed to low (present day; L-CO2) and high (1300ppm; H-CO2) pCO2. Results showed that under H-CO2 the cell specific division rate (µc) was higher and the CO2- and light-saturated photosynthetic rates (Vmax and Pmax) doubled. The cells' photosynthetic affinity for CO2 (K0.5CO2) was halved compared to L-CO2 cultures. However, no significant differences were found in dark respiration rates (Rd), pigment composition and light harvesting efficiency (α). In H-CO2 cells, non-photochemical quenching (NPQ), associated with state transitions of the electron transport chain (ETC), was negligible. Simultaneously, a reorganisation of PSII features including antenna connectivity (JconPSIIα), heterogeneity (PSIIα/ß) and effective absorption cross sectional area (σPSIIα/ß) was observed. In relation to different activities of the CCM, our findings suggest that for cells grown under H-CO2: (1) there is down-regulation of CCM activity; (2) the ability of cells to use the harvested light energy is altered; (3) the occurrence of state transitions is likely to be associated with changes of electron flow (cyclic vs linear) through the ETC; (4) changes in PSII characteristics are important in regulating state transitions.

Nutrient-related changes in the toxicity of field blooms of the cyanobacterium, Cylindrospermopsis raciborskii.

Nutrients have the capacity to change cyanobacterial toxin loads via growth-related toxin production, or shifts in the dominance of toxic and nontoxic strains. This study examined the effect of nitrogen (N) and phosphorus on cell division and strain-related changes in production of the toxins, cylindrospermopsins (CYNs) by the cyanobacterium, Cylindrospermopsis raciborskii. Two short-term experiments were conducted with mixed phytoplankton populations dominated by C. raciborskii in a subtropical reservoir where treatments had nitrate (NO3 ), urea (U) and inorganic phosphorus (P) added alone or in combination. Cell division rates of C. raciborskii were only statistically higher than the control on day 5 when U and P were co-supplied. In contrast, cell quotas of CYNs (QCYNS ) increased significantly in treatments where P was supplied, irrespective of whether N was supplied, and this increase was not necessarily related to cell division rates. Increased QCYNS did correlate with an increase in the proportion of the cyrA toxin gene to 16S genes in the C. raciborskii-dominated cyanobacterial population. Therefore, changes in strain dominance are the most likely factor driving differences in toxin production between treatments. Our study has demonstrated differential effects of nutrients on cell division and strain dominance reflecting a C. raciborskii population with a range of strategies in response to environmental conditions.

Effects of light intensity and temperature on Cylindrospermopsis raciborskii (Cyanobacteria) with straight and coiled trichomes: growth rate and morphology.

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju (Ordem Nostocales) is one of the most troublesome bloom-forming species in Brazil. Understanding the population dynamics of the different morphotypes of C. raciborskii (straight and coiled) could assist in the prediction of favourable conditions for the proliferation of this potentially toxin-producing species. The aim of the present study was to assess the effects of two different light intensities and temperatures on the growth rate and morphology of the trichomes of the straight and coiled morphotypes. For such, two non-toxin producing strains of C. raciborskii were used - one with a coiled trichome (ITEP31) and another with a straight trichome (ITEP28). The strains were cultured in BG-11 medium in a climatic chamber under controlled conditions. Two light intensities (30 and 90 µmol.m-2.s-1 ) were combined at temperatures of 21 and 31 °C and the growth rate and morphological changes were analysed. The morphotypes responded differently to the different temperatures and light intensities. Both strains exhibited faster growth velocities when submitted to higher light intensity and temperature. The lower temperature and higher luminosity hampered the development of both strains. Variations in cellular morphology and an absence of akinetes in both strains were related to the lower temperature (21 °C). The coiled morphotype demonstrated considerable phenotype plasticity, changing the morphology of trichome throughout its growth curve. Although molecular analysis does not sustain the separation of the morphotypes as distinct species, their different eco-physiological responses should be considered further knowledge of extreme importance for the population control of these potentially toxic organisms.

Effects of light intensity and temperature on Cylindrospermopsis raciborskii (Cyanobacteria) with straight and coiled trichomes: growth rate and morphology / Efeitos da intensidade luminosa e temperatura em Cylindrospermopsis raciborskii (Cyanobacteria) com tricomas retos e espiralados: taxa de crescimento e morfologia

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju (Ordem Nostocales) is one of the most troublesome bloom-forming species in Brazil. Understanding the population dynamics of the different morphotypes of C. raciborskii (straight and coiled) could assist in the prediction of favourable conditions for the proliferation of this potentially toxin-producing species. The aim of the present study was to assess the effects of two different light intensities and temperatures on the growth rate and morphology of the trichomes of the straight and coiled morphotypes. For such, two non-toxin producing strains of C. raciborskii were used - one with a coiled trichome (ITEP31) and another with a straight trichome (ITEP28). The strains were cultured in BG-11 medium in a climatic chamber under controlled conditions. Two light intensities (30 and 90 µmol.m-2.s-1 ) were combined at temperatures of 21 and 31 °C and the growth rate and morphological changes were analysed. The morphotypes responded differently to the different temperatures and light intensities. Both strains exhibited faster growth velocities when submitted to higher light intensity and temperature. The lower temperature and higher luminosity hampered the development of both strains. Variations in cellular morphology and an absence of akinetes in both strains were related to the lower temperature (21 °C). The coiled morphotype demonstrated considerable phenotype plasticity, changing the morphology of trichome throughout its growth curve. Although molecular analysis does not sustain the separation of the morphotypes as distinct species, their different eco-physiological responses should be considered further knowledge of extreme importance for the population control of these potentially toxic organisms.

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju (Ordem Nostocales) é uma das espécies formadoras de florações mais prejudiciais no Brasil. Entender a dinâmica populacional dos diferentes morfotipos de C. raciborskii (reto e espiralado) pode auxiliar a previsão de condições favoráveis à proliferação e ao estabelecimento dessa espécie potencialmente produtora de saxitoxinas e cilindrospermopsina. O objetivo deste estudo foi avaliar os efeitos de duas diferentes intensidades luminosas e temperaturas na velocidade de crescimento e na morfologia dos tricomas de morfotipos reto e espiralado. Para tanto, foram utilizadas duas linhagens de C. raciborskii, não produtoras de toxinas, sendo uma com tricoma espiralado (ITEP31) e outra com tricoma reto (ITEP28), cultivadas em câmaras climáticas sob condições controladas em meio BG-11. Duas intensidades luminosas, 30 e 90 µmol.m-2.s-1 , foram combinadas com temperaturas de 21 e 31 °C e avaliadas as velocidades de crescimento e modificações morfológicas. Os morfotipos responderam de maneiras diferentes às temperaturas e intensidades luminosas. As linhagens investigadas, independentemente do morfotipo, apresentaram maiores velocidades de crescimento em intensidade luminosa e temperatura altas. A condição de temperatura baixa e intensidade luminosa alta prejudicaram o desenvolvimento de ambas as linhagens. Variações na morfometria celular, bem como a ausência de acinetos para ambas as linhagens, estiveram relacionadas às condições de temperatura baixa (21 °C). O morfotipo espiralado apresentou grande plasticidade fenotípica, alterando a morfologia do tricoma ao longo de sua curva de crescimento. Apesar de a análise com ferramentas moleculares não sustentar a separação dos morfotipos em espécies distintas, devem-se considerar as diferentes respostas ecofisiológicas entre os mesmos como conhecimento de extrema importância no controle populacional desses organismos potencialmente tóxicos.

The smallest known genomes of multicellular and toxic cyanobacteria: comparison, minimal gene sets for linked traits and the evolutionary implications.

Cyanobacterial morphology is diverse, ranging from unicellular spheres or rods to multicellular structures such as colonies and filaments. Multicellular species represent an evolutionary strategy to differentiate and compartmentalize certain metabolic functions for reproduction and nitrogen (N(2)) fixation into specialized cell types (e.g. akinetes, heterocysts and diazocytes). Only a few filamentous, differentiated cyanobacterial species, with genome sizes over 5 Mb, have been sequenced. We sequenced the genomes of two strains of closely related filamentous cyanobacterial species to yield further insights into the molecular basis of the traits of N(2) fixation, filament formation and cell differentiation. Cylindrospermopsis raciborskii CS-505 is a cylindrospermopsin-producing strain from Australia, whereas Raphidiopsis brookii D9 from Brazil synthesizes neurotoxins associated with paralytic shellfish poisoning (PSP). Despite their different morphology, toxin composition and disjunct geographical distribution, these strains form a monophyletic group. With genome sizes of approximately 3.9 (CS-505) and 3.2 (D9) Mb, these are the smallest genomes described for free-living filamentous cyanobacteria. We observed remarkable gene order conservation (synteny) between these genomes despite the difference in repetitive element content, which accounts for most of the genome size difference between them. We show here that the strains share a specific set of 2539 genes with >90% average nucleotide identity. The fact that the CS-505 and D9 genomes are small and streamlined compared to those of other filamentous cyanobacterial species and the lack of the ability for heterocyst formation in strain D9 allowed us to define a core set of genes responsible for each trait in filamentous species. We presume that in strain D9 the ability to form proper heterocysts was secondarily lost together with N(2) fixation capacity. Further comparisons to all available cyanobacterial genomes covering almost the entire evolutionary branch revealed a common minimal gene set for each of these cyanobacterial traits.

Effects of oxidative and physical treatments on inactivation of Cylindrospermopsis raciborskii and removal of cylindrospermopsin.

The presence of toxic cyanobacterial blooms (or blue-green algae) in water bodies used either as drinking water or for recreational purposes may present serious health risks for the human population. In this study, the removal of the chemical toxin, cylindrospermopsin, via free chlorine, chlorine dioxide, monochloramine, permanganate, ozone, and UV irradiation was studied. Ozone and free chlorine were found to be highly effective for cylindrospermopsion removal while the other disinfectants were ineffective. Ozone and free chlorine were also determined to be highly effective for the inactivation of the cyanobacteria, Cylindrospermopsis raciborskii, at typical water treatment exposures, chlorine dioxide, monochloramine, and permanganate were only marginally effective at inactivation of Cylindrospermopsis raciborskii.

First report of cyanobacterium Cylindrospermopsis raciborskii from Algerian freshwaters.

This study investigated the first report of the cyanobacterium Cylindrospermopsis raciborskii in Algerian freshwaters. The morphological characteristics of the two morphotypes observed in Lake Oubeira (Algeria) conformed to those of natural populations of C. raciborskii species described in the literature. The two morphotypes produced only straight trichomes. During the study (February 2000-September 2001), this species occurred as a codominant with Microcystis spp., and a peak was observed during the autumn (November 2000) with a remarkable density estimated to be 43 x 10(5) trichomes/L. However, difficulty in isolating and culturing these two morphotypes limited the evaluation of their toxic potential.

Morphology, genetic diversity, temperature tolerance and toxicity of Cylindrospermopsis raciborskii (Nostocales, Cyanobacteria) strains from Thailand and Japan.

Cylindrospermopsis raciborskii is a planktonic, nostocalean cyanobacterium, which produces an alkaloid heptatoxin, cylindrospermopsin. We performed morphological observations, 16S rDNA sequence analysis, PCR fingerprint analysis of short tandemly repeated repetitive (STRR) sequences, temperature tolerances and toxin analysis to characterize 24 strains of this toxic cyanobacterium isolated from Thailand and Japan. All strains shared common morphological traits characteristic of C. raciborskii and showed high 16S rDNA sequence similarity, forming a defined cluster together with the reference strains from Australia. In particular, some of the Thai strains shared 99.9% to 100% similarity with the Australian strains. Various combinations of STRR primers revealed different and unique DNA band patterns among strains of C. raciborskii. The phylogenetic tree revealed two main clusters of C. raciborskii strains, the Thai/Japan-Shinobazugaike cluster (cluster I) and the Japan-Gonoike cluster (cluster II). Cluster I was further divided into two subclusters, A (only Thai strains) and B (one Thai strain and the Japan-Shinobazugaike strains). Thus, the results from 16S rDNA and STRR analyses showed no clear geographical distinction between Japanese and Thai strains and between Thai and Australian strains. Thai strains were separated into adaptive and non-adaptive groups to low temperature (15 and 17.5 degrees C) and Japanese strains were composed of only low-temperature-adaptive ones. The toxin cylindrospermopsin was detected in some strains of cluster I-A and in one strain of cluster II. We conclude that C. raciborskii is a species that has recently begun to invade, and a species with different physiological strains or ecotypes in temperature tolerance; the toxin is synthesized without any relation to phylogenetic or genetic clusters and to geography.