The public health, tourism, fisheries, and ecosystem impacts from harmful algal blooms (HABs) have all increased over the past few decades. This has led to heightened scientific and regulatory attention, and the development of many new technologies and approaches for research and management. This, in turn, is leading to significant paradigm shifts with regard to, e.g., our interpretation of the phytoplankton species concept (strain variation), the dogma of their apparent cosmopolitanism, the role of bacteria and zooplankton grazing in HABs, and our approaches to investigating the ecological and genetic basis for the production of toxins and allelochemicals. Increasingly, eutrophication and climate change are viewed and managed as multifactorial environmental stressors that will further challenge managers of coastal resources and those responsible for protecting human health. Here we review HAB science with an eye toward new concepts and approaches, emphasizing, where possible, the unexpected yet promising new directions that research has taken in this diverse field.

https://www.whoi.edu/fileserver.do?id=201484&pt=2&p=28251

Progress in understanding harmful algal blooms: paradigm shifts and new technologies for research, monitoring, and management.

Cyanobacterial secondary metabolites have attracted increasing scientific interest due to bioactivity of many compounds in various test systems. Among the known structures, oligopeptides are often found with many congeners sharing conserved substructures, while being highly variable in others. A major part of known oligopeptides are of non-ribosomal origin and can be grouped into classes with conserved structural properties. Thus, the overall structural diversity of cyanobacterial oligopeptides only seemingly suggests an equally high diversity of biosynthetic pathways and respective genes. For each class of peptides, some of which have been found in all major branches of the cyanobacterial evolutionary tree, homologous synthetases and genes can be inferred. This implies that non-ribosomal peptide synthetase genes are a very ancient part of the cyanobacterial genome and presumably have evolved by recombination and duplication events to reach the present structural diversity of cyanobacterial oligopeptides. In addition, peptide synthetases would appear to be an essential part of the cyanobacterial evolution and physiology. The present review presents an overview of the biosynthesis of cyanobacterial peptides and corresponding gene clusters, the structural diversity of structural types and structural variations within peptide classes, and implications for the evolution and plasticity of biosynthetic genes and the potential function of cyanobacterial peptides.

Cyanobacterial peptides – Nature's own combinatorial biosynthesis

Modern life is intimately linked to the availability of fossil fuels, which continue to meet the world's growing energy needs even though their use drives climate change, exhausts finite reserves and contributes to global political strife. Biofuels made from renewable resources could be a more sustainable alternative, particularly if sourced from organisms, such as algae, that can be farmed without using valuable arable land. Strain development and process engineering are needed to make algal biofuels practical and economically viable.

Exploiting diversity and synthetic biology for the production of algal biofuels

https://epic.awi.de/33380/2/Alexrev_Anderson_Harmful_Algae_2012.pdf

The globally distributed genus Alexandrium: multifaceted roles in marine ecosystems and impacts on human health.

https://www.int-res.com/articles/meps/207/m207p225.pdf

Marine chemical ecology

It is considered self-evident that chemical interactions are a component of competition in terrestrial systems, but they are largely unknown in aquatic systems. In this review, we propose that chemical interactions, specifically allelopathy, are an important part of phytoplankton competition. Allelopathy, as defined here, applies only to the inhibitory effects of secondary metabolites produced by one species on the growth or physiological function of another phytoplankton species. A number of approaches are used to study allelopathy, but there is no standard methodology available. One of the methods used is cross-culturing, in which the cell-free filtrate of a donor alga is added to the medium of the target species. Another is to study the effect of cell extracts of unknown constituents, isolated exudates or purified allelochemicals on the growth of other algal species. There is a clear lack of controlled field experiments because few allelochemicals have been identified. Molecular methods will be important in future to study the expression and regulation of allelochemicals. Most of the identified allelochemicals have been described for cyanobacteria but some known toxins of marine dinoflagellates and freshwater cyanobacteria also have an allelochemical effect. The mode of action of allelochemicals spans a wide range. The most common effect is to cause cell lysis, blistering, or growth inhibition. The factors that affect allelochemical production have not been studied much, although nutrient limitation, pH, and temperature appear to have an effect. The evolutionary aspects of allelopathy remain largely unknown, but we hypothesize that the producers of allelochemicals should gain a competitive advantage over other phytoplankton. Finally, we discuss the possibility of using allelochemicals to combat harmful algal blooms (HABs). Allelopathic agents are used for biological control in agriculture, e.g. green manures to control soil diseases in Australia, but they have not yet been applied in the context of HABs. We suggest that phytoplankton allelochemicals have the potential for management of HABs in localized areas. (Less)

Allelopathy in phytoplankton - biochemical, ecological and evolutionary aspects

The allelopathic effect of Prymnesium parvum (Prymnesiophyta), which produces tox- ins with haemolytic, ichthyotoxic and cytotoxic properties, was investigated on a natural plankton community. Under controlled conditions, 3 laboratory bioassays were performed by adding cell-free filtrate from a P. parvum culture into different size fractions (<150, <100 and 20 to 150 µm) of a nat- ural Baltic Sea plankton community. The effect of P. parvum cell-free filtrate was determined by mea- suring chlorophyll a, cell numbers (phytoplankton, ciliates, bacteria), carbon ( 14 C) uptake by phyto- plankton and the incorporation of 3 H-leucine by bacteria. P. parvum cell-free filtrate affected the whole phytoplankton community, resulting in a decrease in both chlorophyll a and carbon uptake. Furthermore, the plankton groups present in the community exhibited different sensitivity to the cell- free filtrate. While growth of cyanobacteria and dinoflagellates was inhibited, that of diatoms and ciliates was not only completely suppressed, but no cells were present at the end of the experiment in the bottles with P. parvum filtrate. In all experiments, therefore, cyanobacteria and dinoflagellates were the most resistant groups, which led to their dominance in the treatments with filtrate compared to controls. Bacterial production was also negatively affected by P. parvum filtrate. The results show that compounds released by P. parvum induce changes in the plankton community structure, killing other members of the marine food-web, especially other phytoplankton (allelopathy), and suggest that secreted compounds of P. parvum are inhibitory to potential grazers (ciliates). It is proposed that allelopathy is an important process in the ecology of P. parvum.

/pdf/allelopathic-effect-of-prymnesium-parvum-on-a-natural-4y3r62rq25.pdf

Allelopathic effect of Prymnesium parvum on a natural plankton community

Allelopathic effects of the Baltic cyanobacteria Nodularia spumigena, Aphanizomenon flos-aquae and Anabaena lemmermannii on algal monocultures

We studied allelopathy in the dinoflagellate genus Alexandrium by testing the effect of A. tamarense on a natural plankton community from Hopavagen Bay, Trondheimsfjord, Norway, and the effect of toxic and non-toxic strains of A. tamarense and a toxic strain of A. minutum on algal monocultures. Also, a possible relation between the allelopathic effect and the production of paralytic shellfish poison (PSP) toxin was investigated. A. tamarense affected the whole phytoplankton community by decreasing the growth rate and changing the community structure (relative abun- dance of each species, dominant species). A negative effect of A. tamarense was also observed on cil- iates, but not on bacteria numbers. In the bioassay with algal monocultures, the diatom Thalassiosira weissflogii and the cryptophyte Rhodomonas sp. were exposed to the filtrate of Alexandrium spp. All tested Alexandrium strains negatively affected T. weissflogii and Rhodomonas sp. cultures, indepen- dent of whether PSP toxins were produced. The compounds released by Alexandrium caused lysis of natural and cultured algal cells, suggesting that the allelopathic effect may be connected with previ- ously described ichthyotoxic and haemolytic properties of Alexandrium. Furthermore, the observa- tion that several components of the plankton community were affected by compounds released by A. tamarense emphasizes the importance of allelopathy for the ecology of this species.

/pdf/allelopathy-in-alexandrium-spp-effect-on-a-natural-plankton-2kjzp6nagu.pdf

Allelopathy in Alexandrium spp.: effect on a natural plankton community and on algal monocultures

We investigated the effects of cell-free filtrates of the cyanobacteria Nodularia spumigena, Aphanizomenon sp. and Anabaena sp. on a brackish-water plankton community (< 150 mu m). In a laboratory experiment, we monitored the concentration of chlorophyll a and cell numbers of bacteria, phytoplankton and ciliates in the experimental units treated with cyanobacterial filtrates and the control medium. Cyanobacterial filtrates altered the cell numbers of many phytoplankton groups; they stimulated both colonial (Snowella spp.) and filamentous cyanobdcteria (Pseudanabaena spp., Anabaena spp., Aphanizomenon sp., N, spumigena), a chlorophyte (Oocystis sp.), a dinoflagellate (Amphidinium sp.) and nanoflagellates, but inhibited cryptophytes. The filtrates also increased the numbers of bacteria at the beginning of the experiment, whereas they had no effect on ciliate abundances. Our results suggest that cyanobacteria may enhance the effects of eutrophication by stimulating various phytoplankton groups. The specific compounds causing this stimulation remain to be studied. On the other hand, cyanobacteria also seem able to reduce the biomass of certain phytoplankton species, via an allelopathic mechanism. (Less)

/pdf/effects-of-cyanobacterial-allelochemicals-on-a-natural-3wvthhm5oc.pdf

Giovana O. Fistarol

Papers

Allelopathy in phytoplankton - biochemical, ecological and evolutionary aspects

Allelopathic effect of Prymnesium parvum on a natural plankton community

Allelopathic effects of the Baltic cyanobacteria Nodularia spumigena, Aphanizomenon flos-aquae and Anabaena lemmermannii on algal monocultures

Allelopathy in Alexandrium spp.: effect on a natural plankton community and on algal monocultures

Effects of cyanobacterial allelochemicals on a natural plankton community