Marcelo Manzi Marinho

Influence of N/P ratio on competitive abilities for nitrogen and phosphorus by Microcystis aeruginosa and Aulacoseira distans

Microcystis aeruginosa and Aulacoseira distans strains were grown in batch cultures to investigate the consequences of N/P ratio on the growth of these species and on their abilities to take up nitrogen and phosphorus. N/P ratio did not influence the growth rates, which were similar under all the experimental conditions. However, exponential growth lasted longer in Microcystis than in Aulacoseira, especially under low N/P ratio conditions. Distinct patterns of nutrient uptake for Aulacoseira and Microcystis were observed. N-uptake was higher in Microcystis, but not influenced by N/P ratio. However, the amount absorbed was proportional to the concentration in the culture medium for both strains studied. Although Microcystis showed lower uptake of N per biomass unit, a greater yield of Microcystis growth relative to the diatom was observed. This could have resulted from its ability to produce biomass using less nitrogen per unit of biomass. A variation of N/P ratio in the culture medium during the growth of both species was observed. This owed to the uptake of nutrients, with Microcystis showing greater potential than Aulacoseira to influence the N/P ratio. Thus, in contrast to what has been stated in the literature, our results indicated that a low N/P ratio could be a consequence of the capacities and rates of cyanobacterial uptake of nitrogen and phosphorus.

Light and Phosphate Competition Between Cylindrospermopsis raciborskii and Microcystis aeruginosa is Strain Dependent

The hypothesis that outcomes of phosphorus and light competition between Cylindrospermopsis raciborskii and Microcystis aeruginosa are strain dependent was tested experimentally. Critical requirements of phosphorus (P*) and of light (I*) of two strains of each species were determined through monoculture experiments, which indicated a trade-off between species and also between Microcystis strains. Competition experiments between species were performed using the weakest predicted competitors (with the highest values of P* and of I*) and with the strongest predicted competitors (with the lowest values of P* and of I*). Under light limitation, competition between the weakest competitors led C. raciborskii to dominate. Between the strongest competitors, the opposite was observed, M. aeruginosa displaced C. raciborskii, but both strains co-existed in equilibrium. Under phosphate limitation, competition between the weakest competitors led C. raciborskii to exclude M. aeruginosa, and between the strongest competitors, the opposite was observed, M. aeruginosa displaced C. raciborskii, but the system did not reach an equilibrium and both strains were washed out. Hence, outcomes of the competition depended on the pair of competing strains and not only on species or on type of limitation. We concluded that existence of different trade-offs among strains and between species underlie our results showing that C. raciborskii can either dominate or be displaced by M. aeruginosa when exposed to different conditions of light or phosphate limitation.

The efficiency of combined coagulant and ballast to remove harmful cyanobacterial blooms in a tropical shallow system

We tested the hypothesis that a combination of coagulant and ballast could be efficient for removal of positively buoyant harmful cyanobacteria in shallow tropical waterbodies, and will not promote the release of cyanotoxins. This laboratory study examined the efficacy of coagulants [polyaluminium chloride (PAC) and chitosan (made of shrimp shells)] alone, and combined with ballast (lanthanum modified bentonite, red soil or gravel) to remove the natural populations of cyanobacteria collected from a shallow eutrophic urban reservoir with alternating blooms of Cylindrospermopsis and Microcystis. PAC combined with ballast was effective in settling blooms dominated by Microcystis or Cylindrospermopsis. Contrary to our expectation, chitosan combined with ballast was only effective in settling Cylindrospermopsis-dominated blooms at low pH, whereas at pH≥8 no effective flocculation and settling could be evoked. Chitosan also had a detrimental effect on Cylindrospermopsis causing the release of saxitoxins. In contrast, no detrimental effect on Microcystis was observed and all coagulant-ballast treatments were effective in not only settling the Microcystis dominated bloom, but also lowering dissolved microcystin concentrations. Our data show that the best procedure for biomass reduction also depends on the dominant species.

Assessment of possible solid-phase phosphate sorbents to mitigate eutrophication: Influence of pH and anoxia

Managing eutrophication remains a challenge to water managers. Currently, the manipulation of biogeochemical processes (i.e., geo-engineering) by using phosphorus-adsorptive techniques has been recognized as an appropriate tool to manage the problem. The first step in finding potential mitigating materials is conducting a sequence of upscaling studies that commence with controlled laboratory experiments. Here, the abilities of 10 possible solid-phase-sorbents (SPS) to adsorb P were examined. Four materials adsorbed P, and two of these materials were modified, i.e., a lanthanum-modified-bentonite (LMB) and an aluminum-modified-zeolite (AMZ), and had the highest adsorption capacities of 11.4 and 8.9mgPg-1, respectively. Two natural materials, a red soil (RS) and a bauxite (BAU), were less efficient with adsorption capacities of 2.9 and 3.4mgPg-1, respectively. Elemental composition was not related to P adsorption. Since SPS might be affected by pH and redox status, we also tested these materials at pH values of 6, 7, 8 and 9 and under anoxic condition. All tested materials experienced decreased adsorption capacities under anoxic condition, with maximum adsorptions of 5.3mgPg-1 for LMB, 5.9mgPg-1 for AMZ, 0.2mgPg-1 for RS and 0.2mgPg-1 for BAU. All materials were able to adsorb P across the range of pH values that were tested. The maximum adsorption capacities of LMB and RS were highest at pH6, AMZ was higher at a pH of 9 and BAU at a pH of 8. Thus, pH influenced P adsorption differently. Given the effects of pH and anoxia, other abiotic variables should also be considered. Considering the criteria that classify a useful SPS (i.e., effective, easy to produce, cheap and safe), only the two modified materials that were tested seem to be suitable for upscaling to enclosure studies with anoxic sediments.

5 – BIOMASSA FITOPLANCTÔNICA E PRODUÇÃO PRIMÁRIA*

RESUMO A caracterizacao da variabilidade espaco-temporal da biomassa fitoplanctonica e da produtividade primaria da Bacia de Campos foi observada durante duas campanhas oceanograficas realizadas entre marco e abril (periodo chuvoso) e agosto e setembro (periodo seco) de 2009. Durante estas campanhas foram coletadas amostras na superficie e na base da camada de mistura em cinco transectos no periodo chuvoso e quatro no periodo seco, cujas estacoes variaram entre 25 e 3.000 m de profundidade. A concentracao de clorofila a total (mono- e divinil-) apresentou um gradiente decrescente do continente para a regiao oceânica, variando de 0,20 a 1,80 μg·L−1 e 0,10 a 7,83 μg·L−1 na regiao neritica e nos periodos chuvoso e seco, respectivamente. Na regiao oceânica a concentracao variou entre 0,04 e 0,33 μg·L−1 em ambos os periodos do ano. A divinil-clorofila a foi detectada em grande parte da Bacia de Campos com concentracoes variando ate 0,15 μg·L−1 e apresentou padrao de distribuicao inverso ao da clorofila a total, com gradiente longitudinal crescente ao longo da regiao oceânica, chegando a representar 40% da clorofila a total nessas regioes. A produtividade primaria foi avaliada por meio de experimentos in situ simulados para a construcao das curvas de luz-fotossintese e consequente estimativa dos parâmetros fotossinteticos, que foram utilizados para o calculo da produtividade primaria integrada na zona eufotica. Os valores de produtividade primaria variaram de 0,07 a 1,56 gC·m−2·d−1 no periodo chuvoso, e de 0,34 a 0,57 gC·m−2·d−1 no periodo seco, nao havendo diferenca significativa entre os dois periodos. Os resultados obtidos confirmam a caracteristica oligotrofica da regiao da Bacia de Campos, com excecao das regioes proximas de Cabo Frio e Cabo Sao Tome, que estao sujeitas a influencia de feicoes oceanograficas que aportam nutrientes.

Coagulant plus ballast technique provides a rapid mitigation of cyanobacterial nuisance

Cyanobacteria blooms are a risk to environmental health and public safety due to the potent toxins certain cyanobacteria can produce. These nuisance organisms can be removed from water bodies by biomass flocculation and sedimentation. Here, we studied the efficacy of combinations of a low dose coagulant (poly-aluminium chloride—PAC—or chitosan) with different ballast compounds (red soil, bauxite, gravel, aluminium modified zeolite and lanthanum modified bentonite) to remove cyanobacterial biomass from water collected in Funil Reservoir (Brazil). We tested the effect of different cyanobacterial biomass concentrations on removal efficiency. We also examined if zeta potential was altered by treatments. Addition of low doses of PAC and chitosan (1–8 mg Al L-1) to the cyanobacterial suspensions caused flock formation, but did not settle the cyanobacteria. When those low dose coagulants were combined with ballast, effective settling in a dose-dependent way up to 99.7% removal of the flocks could be achieved without any effect on the zeta potential and thus without potential membrane damage. Removal efficacy was influenced by the cyanobacterial biomass and at higher biomass more ballast was needed to achieve good removal. The combined coagulant-ballast technique provides a promising alternative to algaecides in lakes, ponds and reservoirs.

COMPOSIÇÃO DO FITOPLÂNCTON A PARTIR DA AVALIAÇÃO DE PIGMENTOS MARCADORES (CAROTENOIDES E CLOROFILAS)

RESUMO A composicao das comunidades fitoplanctonicas na Bacia de Campos (BC) foi estudada atraves de pigmentos marcadores durante duas campanhas oceanograficas realizadas entre marco e abril (periodo chuvoso – PC) e agosto e setembro (periodo seco – PS) de 2009. Foram coletadas amostras na superficie (1 m) e na base da camada de mistura, em nove transectos (da regiao costeira a oceânica) no PC e no PS. Os pigmentos foram analisados por cromatografia liquida de alta eficiencia (HPLC, sigla em ingles). O software CHEMTAX foi utilizado para estimar, a partir dos pigmentos, a contribuicao dos diferentes grupos fitoplanctonicos para a clorofila a total (TCla). A biomassa fitoplanctonica estimada pela TCla apresentou grande variacao na area da Bacia de Campos, sendo observado um gradiente decrescente da regiao neritica para a regiao oceânica. Os valores observados nas aguas da regiao neritica podem ser considerados tipicos de regioes costeiras (maximo de 1,86 μg·L−1 no PC e 5,51 μg·L−1 no PS). As concentracoes registradas na regiao oceânica sao caracteristicas de sistemas oligotroficos como as aguas da Corrente do Brasil (0,03 a 0,3 μg·L−1 no PC e 0,06 a 0,6 μg·L−1 no PS). A abordagem quimiotaxonomica registrou a presenca de sete classes fitoplanctonicas que apresentaram padroes espaciais ao longo dos perfis batimetrico e vertical, mas nao foram identificados padroes de distribuicao latitudinais. Em geral os grupos fitoplanctonicos tiveram biomassas mais elevadas durante o periodo seco, mas as cianobacterias tiveram as maiores biomassas registradas no periodo chuvoso. Foram observados distintos padroes espaciais no perfil batimetrico. As diatomaceas apresentaram biomassas elevadas nas primeiras isobatas (25 e 50 m), enquanto organismos nanoflagelados (primnesioficeas, prasinoficeas e criptoficeas) mostraram gradiente decrescente ao longo do perfil batimetrico. O picoplâncton eucariotico (pelagoficeas) apresentou gradiente crescente em direcao a quebra da plataforma continental e posterior decrescimo na regiao oceânica. Em relacao as cianobacterias, Trichodesmium (microplâncton), registrado apenas no periodo chuvoso, e Synechococcus (picoplâncton) apresentaram ampla distribuicao em toda Bacia de Campos e maiores biomassas na superficie. Prochlorococcus, outra cianobacteria picoplanctonica registrada, apresentou um padrao semelhante ao das pelagoficeas na campanha do periodo chuvoso, contudo, no periodo seco esteve presente sobretudo na regiao oceânica, apresentando biomassas crescentes a partir da isobata de 150 m. Ao longo do perfil batimetrico pode ser identificado um gradiente da regiao neritica, onde ha maior disponibilidade de nutrientes, para as aguas oceânicas mais oligotroficas, com mudancas na abundância, estrutura de tamanho e composicao taxonomica das assembleias fitoplanctonicas, passando de biomassas mais elevadas do microplâncton para picoplâncton de biomassas reduzidas.

Critical assessment of chitosan as coagulant to remove cyanobacteria

Removal of cyanobacteria from the water column using a coagulant and a ballast compound is a promising technique to mitigate nuisance. As coagulant the organic, biodegradable polymer chitosan has been promoted. Results in this study show that elevated pH, as may be common during cyanobacterial blooms, as well as high alkalinity may hamper the coagulation of chitosan and thus impair its ability to effectively remove positively buoyant cyanobacteria from the water column. The underlying mechanism is likely a shielding of the protonated groups by anions. Inasmuch as there are many chitosan formulations, thorough testing of each chitosan prior to its application is essential. Results obtained in glass tubes were similar to those from standard jar tests demonstrating that glass tube tests can be used for testing effects of coagulants and ballasts in cyanobacteria removal whilst allowing far more replicates. There was no relation between zeta potential and precipitated cyanobacteria. Given the well-known antibacterial activity of chitosan and recent findings of anti-cyanobacterial effects, pre-application tests are needed to decipher if chitosan may cause cell leakage of cyanotoxins. Efficiency- and side-effect testing are crucial for water managers to determine if the selected approach can be used in tailor-made interventions to control cyanobacterial blooms and to mitigate eutrophication.

Cyanobacteria dominance drives zooplankton functional dispersion

Accelerated eutrophication reduces water quality and shifts plankton communities. However, its effects on the aquatic food web and ecosystem functions remain poorly understood. Within this context, functional ecology can provide valuable links relating community traits to ecosystem functioning. In this study, we assessed the effects of eutrophication and cyanobacteria blooms on zooplankton functional diversity in a tropical hypereutrophic lake. Phytoplankton and zooplankton communities and limnological characteristics of a tropical Brazilian Lake (Southeast, Brazil) were monitored monthly from April 2013 to October 2014. Lake eutrophication indicators were total phosphorus, total chlorophyll-a, and chlorophyll-a per group (blue, green, and brown). The variation of major phytoplankton taxonomic group biomass was calculated and used as a proxy for changes in phytoplankton composition. Zooplankton functional diversity was assessed through functional dispersion and the community-weighted mean trait value. Regressions were performed between the lake eutrophication indicators, the phytoplankton biomass variation, and zooplankton functional dispersion. Our results suggest that eutrophication and cyanobacterial dominance change the composition of zooplankton traits and reduce functional dispersion, leading to zooplankton niche overlap. These findings are important because they provide a meaningful view of phytoplankton-zooplankton trophic interactions and contribute to an improved understanding their functional effects on aquatic ecosystems.

The Cyanobacterium Cylindrospermopsis raciborskii (CYRF-01) Responds to Environmental Stresses with Increased Vesiculation Detected at Single-Cell Resolution

Secretion of membrane-limited vesicles, collectively termed extracellular vesicles (EVs), is an important biological process of both eukaryotic and prokaryotic cells. This process has been observed in bacteria, but remains to be better characterized at high resolution in cyanobacteria. In the present work, we address the release of EVs by Cylindrospermopsis raciborskii (CYRF-01), a filamentous bloom-forming cyanobacterium, exposed to environmental stressors. First, non-axenic cultures of C. raciborskii (CYRF-01) were exposed to ultraviolet radiation (UVA + UVB) over a 6 h period, which is known to induce structural damage to this species. Second, C. raciborskii was co-cultured in interaction with another cyanobacterium species, Microcystis aeruginosa (MIRF-01), over a 24 h period. After the incubation times, cell density and viability were analyzed, and samples were processed for transmission electron microscopy (TEM). Our ultrastructural analyses revealed that C. raciborskii constitutively releases EVs from the outer membrane during its normal growth and amplifies such ability in response to environmental stressors. Both situations induced significant formation of outer membrane vesicles (OMVs) by C. raciborskii compared to control cells. Quantitative TEM revealed an increase of 48% (UV) and 60% (interaction) in the OMV numbers compared to control groups. Considering all groups, the OMVs ranged in size from 20 to 300 nm in diameter, with most OMVs showing diameters between 20 and 140 nm. Additionally, we detected that OMV formation is accompanied by phosphatidylserine exposure, a molecular event also observed in EV-secreting eukaryotic cells. Altogether, we identified for the first time that C. raciborskii has the competence to secrete OMVs and that under different stress situations the genesis of these vesicles is increased. The amplified ability of cyanobacteria to release OMVs may be associated with adaptive responses to changes in environmental conditions and interspecies cell communication.