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

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ecofisiologia de morfotipos reto e espiralado de Cylindrospermopsis raciborskii (Cyanobacteria) em condições controladas

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

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 mu mol.m(-2).s(-1)) were combined at temperatures of 21 and 31 degrees 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.

Morphological changes during akinete germination in Cylindrospermopsis raciborskii (Nostocales, Cyanobacteria)

The occurrence of the cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju is a global water quality issue. The misidentification of C. raciborskii in the past is a major concern for water quality users, considering the reported cases of human and livestock poisonings associated with the cyanobacterium. Many of the available taxonomic descriptions for this species provide little or no detail of the morphology of early developmental phases that may assist with identification. Therefore, typifying the morphological changes throughout the entire life cycle for such a species requires urgent attention. In this study, five distinct morphological phases identified using a new culturing technique are reported for the process of akinete germination in C. raciborskii. Before the terminal emergence of three to four cell germlings through a ruptured akinete envelope (phase 3), mature akinetes (phase 1) elongated and the endospore separated from the akinete envelope (phase 2). After the association with the envelope was lost, four-cell germlings (phase 4a) matured into young trichomes of more than four cells (phase 4b). Throughout the process of germination, internal granular structures decreased in size and were irregular in shape in germlings and young trichomes. The culturing technique, which used a Sedgwick-Rafter cell, was successful in its application but was limiting in that the development of young trichomes after phase 4b could not be monitored.

Factors affecting akinete differentiation in Cylindrospermopsis raciborskii (Nostocals, Cyanobacteria)

1. Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium which can produce akinetes (reproductive spores) that on germinating can contribute to future populations. To further understand factors controlling the formation of these specialised cells, the effects of diurnal temperature fluctuations (magnitude and frequency), in combination with different light intensities and phosphorus concentrations were investigated under laboratory conditions. 2. Akinete differentiation was affected by the frequency of temperature fluctuations. Maximum akinete concentrations were observed in cultures that experienced multiple diurnal temperature fluctuations. 3. Akinete concentrations increased with increasing magnitude of temperature fluctuation. A maximum akinete concentration was achieved under multiple diurnal temperature fluctuations with a magnitude of 10degreesC (25degreesC to 15degreesC). 4. A fourfold increase in light intensity (25-100 mumol m(-2) s(-1)) resulted in an approximate 14-fold increase in akinete concentration. 5. High filterable reactive phosphorus (FRP) concentrations (> 70 mug L-1) in the medium, combined with a multiple diurnal temperature fluctuation of 10degreesC, supported the development of the highest akinete concentration.

Comparative studies on photosynthesis and phosphate metabolism of Cylindrospermopsis raciborskii with Microcystis aeruginosa and Aphanizomenon flos-aquae

The physiological differences for three bloom-forming cyanobacteria (Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Aphanizomenon flos-aquae) were investigated. In comparison with M. aeruginosa and A. flos-aquae, C. raciborskii exhibited a significantly higher concentration of carotenoids, higher values in maximum photosynthesis rate (P-m), apparent photosynthetic efficieny (a), and maximum electron transport rate (ETRmax) during the growth period. In addition, higher extracellular alkaline phosphatase activities and lower light compensation point (I-c) were also detected in C raciborskii (p < 0.05, ANOVA). Therefore, it is suggested that the higher photosynthetic activities, more effective uptake and utilization to phosphate, and low light requirements might play important roles in the occurrence and invasive behavior of C. raciborskii. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Cylindrospermopsis raciborskii exudate-Cu complexes: impact on copper dynamics and bioavailability in an aquatic food chain

The increasing contamination of aquatic environments motivates studies on the interactions among natural dissolved organic matter, metals, and the biota. This investigation focused on the organic exudates of the toxic cyanobacteria Cylindrospermopsis raciborskii as a Cu carrier through a three-level aquatic trophic chain (bacteria, protozoa, and copepod). The effects of bacteria activity and growth on the metal-organic complexes were evaluated through changes in free Cu2+ ions, total dissolved, and total particulate Cu. To be sure that the added copper would be complexed to the exudates, its complexing properties were previously determined. The cyanobacteria exudate-Cu complexes were furnished to bacteria that were further used as a food source to the protozoan Paramercium caudatum. This was then furnished as food to the copepod Mesocyclops sp. The results showed that, in general, the cyanobacterial exudates decreased Cu bioavailability and toxicity to the first trophic level (bacteria), but because the heterotrophic bacteria accumulated Cu, they were responsible for the transference for the otherwise low availability metal form. Both the bacteria and protozoan organisms accumulated Cu, but no metal accumulation was detected in the copepods.

Seasonal dynamics of cyanobacteria in a eutrophic reservoir (Arcoverde) in a semi-arid region of Brazil

Environmental conditions favor the predominance of dense populations of cyanobacteria in reservoirs in northeastern Brazil. The aim of this study was to understand cyanobacterial population dynamics in the rainy and dry seasons at two depths in the Arcoverde reservoir. Microalgae and cyanobacteria samples were collected during 24 hours with intervals of 4 hours (nycthemeral) at sub-surface and 10 m using a van Dorn bottle and a determined biomass. Physical and chemical variables were obtained and the data were analyzed using the principal component analysis (PCA). No nycthemeral variations in the taxonomic composition or distribution of the populations of cyanobacteria were found between the different times of day in either the rainy or dry season. In both seasons, the greatest biomass of the phytoplankton community was made up of cyanobacteria at two depths and all times of the day. Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju was dominant at all times of the day on both the surface and at the bottom. In the rainy season, the differences in cyanobacterial biomass between the surface and bottom were less significant than in the dry season. The differences in cyanobacterial biomass between surface and bottom were less pronounced than those found in the dry season. We concluded that a) physical variables better explain the alterations of species in the phytoplankton community in an environment dominated by cyanobacteria throughout the year; b) seasonal climatic factors associated to periods of stratification and de-stratification are important for alterations in the community and variations in biomass and, c) the turbidity caused by rainfall favored the emergence and establishment of other cyanobacteria, especially Planktothrix agardhii (Gomont) Anagnostidis & Komarek.

Toxicity risks linked to cyanobacteria blooms in southern Portugal reservoirs

Tese de doutoramento, Ciências e Tecnologias do Ambiente, Escola Superior de Saúde, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

Cyanobacteria and Cyanotoxin in the Billings Reservoir (São Paulo, SP, Brazil)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)