An ecologically and economically disruptive harmful algal bloom (HAB) affected much of the northeast Pacific margin in 2015, during a prolonged oceanic warm anomaly. Caused by diatoms of the genus ...Pseudo‐nitzschia, this HAB produced the highest particulate concentrations of the biotoxin domoic acid (DA) ever recorded in Monterey Bay, California. Bloom inception followed strong upwelling during the spring transition, which introduced nutrients and eliminated the warm anomaly locally. Subsequently, moderate and intermittent upwelling created favorable conditions for growth and accumulation of HAB biomass, which was dominated by a highly toxigenic species, P. australis. High cellular DA concentrations were associated with available nitrogen for DA synthesis coincident with silicate exhaustion. This nutrient influence resulted from two factors: (1) disproportionate depletion of silicate in upwelling source waters during the warm anomaly, the most severe depletion observed in 24 years, and (2) silicate uptake by the dense diatom bloom.
Key Points
The most toxic algal bloom ever recorded in Monterey Bay, California, occurred in spring 2015, during a hiatus in a prolonged warm anomaly
The dense bloom of Pseudo‐nitzschia australis resulted from a strong spring upwelling transition followed by intermittent upwelling
Toxicity was influenced by anomalously low ratios of silicate to nitrate that predisposed the bloom to silicate exhaustion
The dinoflagellate,
Cochlodinium polykrikoides Margalef, has been responsible for mass mortalities of both wild and farmed fish along the Korean coast on virtually an annual basis since 1982. ...Economic impacts to the fishing and aquaculture industries are extensive, with a loss of USD $95 million reported in 1995 alone. The use of taxon-specific molecular probes for harmful algal species is recognized as a promising approach for the early detection of bloom formation and as part of an effective mitigation strategy. We have developed and successfully applied large subunit ribosomal RNA (LSU rRNA)-targeted probes in both whole cell and sandwich hybridization assay (SHA) formats for the species-specific detection of
C. polykrikoides in Korean coastal waters. Sequences of the D1–D3 variable regions used to design probes were identical between five Korean and one Hong Kong
C. polykrikoides isolates, while sequences for several N. American
Cochlodinium isolates differed to varying degrees from the former. The automated SHA detected
C. polykrikoides at levels as low as ∼1–3
cells/L in the field, demonstrating its suitability for detecting the target species at pre-bloom concentrations. This method should thus prove valuable to existing monitoring programs aimed at providing aquaculture interests with an early warning of frequently devastating bloom events.
The red tide dinoflagellate
Karenia brevis blooms annually along the eastern Gulf of Mexico, USA, and is often linked to significant economic losses through massive fish kills, shellfish harvest ...closures, and the potential threat to humans of neurotoxic shellfish poisonings as well as exposure to aerosolized toxin. As part of an effort to enhance the strategies employed to manage and mitigate these events and their adverse effects, several approaches are being investigated for controlling blooms. Previous studies have established the presence of algicidal bacteria lethal to
K. brevis in these waters, and we aim to characterize bacterial–algal interactions, evaluate their role as natural regulators of
K. brevis blooms, and ultimately assess possible management applications. Herein, the algicidal activity of a newly isolated
Cytophaga/
Flavobacterium/
Bacteroidetes (CFB)-bacterium, strain S03, and a previously described CFB-bacterium, strain 41-DBG2, was evaluated against various harmful algal bloom (HAB) and non-HAB species (23 total), including multiple clones of
K. brevis, to evaluate algal target specificity. Strains S03 and 41-DBG2, which employ direct and indirect modes of algicidal lysis, respectively, killed ∼20% and ∼40% of the bacteria-containing isolates tested. Interestingly, no bacteria-free algal cultures were resistant to algicidal attack, whereas susceptibility varied occasionally among bacteria-containing isolates of a single algal taxon originating from either the same or different geographic location. The dynamics of
K. brevis culture death appeared to differ according to whether the algicidal bacterium did or did not require direct contact with algal cells, with the former most rapidly affecting
K. brevis morphology and causing cell lysis. Both bacterial strains promoted the formation of a small number of cyst-like structures in the
K. brevis cultures, possibly analogous to temporary cysts formed by other dinoflagellates exposed to certain types of stress. Results were also consistent with earlier work demonstrating that bacterial assemblages from certain cultures can confer resistance to attack by algicidal bacteria, again indicating the complexity and importance of microbial interactions, and the need to consider carefully the potential for using such bacteria in management activities.
The ability to detect harmful algal bloom (HAB) species and their toxins in real- or near real-time is a critical need for researchers studying HAB/toxin dynamics, as well as for coastal resource ...managers charged with monitoring bloom populations in order to mitigate their wide ranging impacts. The Environmental Sample Processor (ESP), a robotic electromechanical/fluidic system, was developed for the autonomous, subsurface application of molecular diagnostic tests and has successfully detected several HAB species using DNA probe arrays during field deployments. Since toxin production and thus the potential for public health and ecosystem effects varies considerably in natural phytoplankton populations, the concurrent detection of HAB species and their toxins onboard the ESP is essential. We describe herein the development of methods for extracting the algal toxin domoic acid (DA) from
Pseudo-nitzschia cells (extraction efficiency >90%) and testing of samples using a competitive ELISA onboard the ESP. The assay detection limit is in the low ng/mL range (in extract), which corresponds to low ng/L levels of DA in seawater for a 0.5
L sample volume acquired by the ESP. We also report the first
in situ detection of both a HAB organism (i.e.,
Pseudo-nitzschia) and its toxin, domoic acid, via the sequential (within 2–3
h) conduct of species- and toxin-specific assays during ESP deployments in Monterey Bay, CA, USA. Efforts are now underway to further refine the assay and conduct additional calibration exercises with the aim of obtaining more reliable, accurate estimates of bloom toxicity and thus their potential impacts.
A bacterial strain (D38BY) belonging to the family Flavobacteriaceae and antagonistic towards an algicidal bacterium (strain S03; Flavobacteriaceae) was isolated from a culture of the red tide ...dinoflagellate Karenia brevis that had previously been characterized as resistant to attack by strain S03. This antagonistic bacterium increased the survival time of otherwise susceptible, bacteria-free K. brevis cultures in a concentration-dependent manner during exposure to the algicidal bacterium. Experimental evidence indicated that direct contact was required in order for strain D38BY to inhibit the killing activity of algicidal strain S03. While further work is needed to determine its precise mode of action, the antagonistic properties of strain D38BY provide further evidence that the resistance or susceptibility of certain algal taxa to algicidal attack can be more a function of interactions within the ambient microbial community than an intrinsic property of the alga.
An unusual isomer of domoic acid (1), isodomoic acid C (2), has been found in New Zealand shellfish contaminated by amnesic shellfish poisoning (ASP) toxins and was shown to be produced by a local ...strain of the pennate diatom Pseudo-nitzschia australis. A bulk culture of this strain was used to isolate 2. The structure was determined from spectroscopic data and was shown to correspond to that of 2 from a Japanese red seaweed, the only other reported occurrence of this compound. The affinity of 2 for GluR6 glutamate receptors was 240-fold lower than for 1, indicating low neurotoxic potential.
There is a need for assay systems that can detect known and unanticipated neurotoxins associated with harmful algal blooms. The present work describes our attempt to monitor the presence of ...brevetoxin-3 (PbTx-3) and saxitoxin (STX) in a seawater matrix using the neuronal network biosensor (NNB). The NNB relies on cultured mammalian neurons grown over microelectrode arrays, where the inherent bioelectrical activity of the network manifested as extracellular action potentials can be monitored noninvasively. Spinal cord neuronal networks were prepared from embryonic mice and the mean spike rate across the network was analyzed before and during exposure to the toxins. Extracellular action potentials from the network are highly sensitive not only to purified STX and PbTx-3, but also when in combination with matrixes such as natural seawater and algal growth medium. Detection limits for STX and PbTx-3, respectively, are 0.031 and 0.33 nM in recording buffer and 0.076 and 0.48 nM in the presence of 25-fold-diluted seawater. Our results demonstrated that neuronal networks could be used for analysis of Alexandrium fundyense (STX-producer) and Karenia brevis (PbTx-producer) algal samples lysed directly in the seawater-based growth medium and appropriately diluted with HEPES-buffered recording medium. The cultured network responded by changes in mean spike rate to the presence of STX- or PbTx-producing algae but not to the samples of two non-STX and non-PbTx isolates of the same algal genera. This work provides evidence that the NNB has the capacity to rapidly detect toxins associated with cells of toxic algal species or as dissolved forms present in seawater and has the potential for monitoring toxin levels during harmful algal blooms.
Phylogenetic relationships among chain-forming
Cochlodinium species, including the harmful red tide forming dinoflagellate
Cochlodinium polykrikoides, were investigated using specimens collected from ...coastal waters of Canada, Hong Kong, Japan, Korea, Malaysia, México, Philippines, Puerto Rico, and USA. The phylogenetic tree inferred from partial (D1–D6 regions) large subunit ribosomal RNA gene (LSU rDNA) sequences clearly differentiated between
C. polykrikoides and a recently described species,
Cochlodinium
fulvescens. Two samples collected from the Pacific coasts of North America (British Columbia, Canada and California, USA) having typical morphological characters of
C. fulvescens such as the sulcus located in the intermediate region of the cingulum, were closely related to
C. fulvescens from western Japan in the phylogenetic tree.
Cochlodinium polykrikoides formed a monophyletic group positioned as a sister group of the
C. fulvescens clade with three well-supported sub-clades. These three clades were composed of (1) East Asian, including specimens collected from Hong Kong, western Japan, and southern Korea, (2) Philippines, from Manila Bay, Philippines and Omura Bay, Japan, and (3) American/Malaysian, from the Atlantic coasts of USA, the Pacific coast of México, Puerto Rico, and Borneo Island, Malaysia. Each of these clades is considered to be a so-called “ribotype” representing the population inhabiting each region, which is distinguished based on ribosomal RNA gene sequences in the species despite similarities in their morphological characters.
Several natural isomers of the seizurogenic neurotoxin domoic acid (DA) have been found to occur at up to mg/kg levels in shellfish. The aim of the current study was to assess the neurotoxic potency ...of isodomoic acids A and C (Iso-A and Iso-C), recently isolated from commercial shellfish. Hippocampal slices were obtained from young adult rats and maintained in a tissue recording chamber. Synaptically evoked population spikes were recorded in region CA1 before and after exposure to DA or its isomers. Both Iso-A and Iso-C produced transient neuronal hyperexcitability followed by a dose-dependent suppression of population spikes, but were, respectively, 4- and 20-fold less potent than DA (spike area: EC
50 DA=237
nM; Iso-A=939
nM; Iso-C=4.6
μM). In the hippocampus, DA preconditioning induces tolerance to subsequent DA toxicity. However, in the present study neither Iso-A nor Iso-C were effective as preconditioning agents. Competitive binding studies using homomeric GluR6 kainate (kainic acid, KA) receptors showed the affinity of Iso-A to be 40-fold lower than DA (
K
i
DA=3.35
nM; Iso-A=130
nM). Together with earlier work showing Iso-C affinity at GluR6 receptors to be 240-fold lower than DA, our results suggest that neuroexcitatory effects of Iso-A in CA1 may involve both
α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and KA receptors, while Iso-C likely involves the activation of AMPA receptors alone.
The brevetoxin producing dinoflagellate,
Karenia brevis, is the target of several monitoring and research programs in the Gulf of Mexico, where it forms extensive and frequently long-lived annual ...blooms that can cause human intoxication and fish kills, as well as severe economic losses to coastal communities. Rapid, reliable methods for the detection and enumeration of
K. brevis cells, as well as their discrimination from morphologically similar species, are valuable tools for managers and scientists alike. Our aim was to produce a species-specific molecular probe that would serve as a tool to facilitate the efficient and reliable detection of
K. brevis in the Gulf of Mexico. We sequenced a fragment of the large-subunit ribosomal RNA gene (LSU rDNA) from five
K. brevis cultures isolated from the Texas Gulf coast, the Florida Gulf coast, and the Atlantic coast of Florida, and detected no differences among these isolates. A consensus sequence was thus compiled and compared to a previously published sequence from
Karenia mikimotoi, the closest known phylogenetic relative to
K. brevis, for the purpose of identifying unique
K. brevis signature sequences. Fluorescently-labeled (FITC) oligonucleotide probes targeting these regions of the
K. brevis LSU rRNA were designed to include at least two base pair differences, as compared to
K. mikimotoi. Among seven probes designed, one uniquely identified all
K. brevis isolates to the exclusion of all other species tested (Kbprobe-7), including a Gulf of Mexico
K. mikimotoi isolate (Sarasota, FL) and several additional
Gymnodinium species, as well as other dinoflagellate, diatom, and raphidophyte taxa. Importantly,
K. brevis cells in samples taken during a 2001 bloom, fixed with a mixture of modified saline ethanol and 10% formalin, and stored at 4
°C for 7 months were successfully labeled with Kbprobe-7. In addition, preliminary analysis of labeled cells by flow cytometry revealed that
K. brevis could be distinguished from
K. mikimotoi in solution, suggesting other potential applications of this probe.
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