Viable gut passage of cyanobacteria through the filter-feeding fish Atlantic menhaden, Brevoortia tyrannus

We examined the contents of the alimentary tract of juvenile Atlantic menhaden, an obligate filter-feeding fish, with epifluoresence microscopy. All plankton taxa and detrital material observed in plankton samples from the sampling area could also be found in the esophagus of the fish. The corresponding plankton taxa were absent from the pre-feces sampled in the hindgut with the exception of cyanobacteria, which were found intact and fluorescing as they do in nature. The survival of cyanobacteria during gut passage and their presence in menhaden feces may enhance both nutrient availability and the delivery of these cells to the benthos. Additionally, diatoms frustules were found in the pre-feces, which may affect the sequestration of biogenic silica. These results may have bearing on the formation of cyanobacteria blooms, nutrient flow in estuaries and the delivery of material to the sediment

Spatial and temporal bacterioplankton dynamics during destratification of the James River estuary, Virginia, USA

Bacterioplankton abundance and production were examined over the course of a destratification event in the lower James River, Virginia, USA, Goals of the study were to determine if destratification would influence temporal patterns of bacterioplankton parameters and relationships between bacterioplankton and other biological and abiological parameters. Mean bacterial abundance grouped over stations did not change over the course of the study, and were characterized by much smaller coefficients of variation than all other planktonic constituents. However, bacterial production measured by H-3-thymidine (H-3-Tdr) incorporation decreased significantly from a stratified (324 mu g Cl-1 d(-1)) to a destratified (187 mu g Cl-1 d(-1)) hydrography. The importance of bacterial-autotrophic coupling was also suggested from oxygen metabolism experiments, which indicated substrate limitation of bacteria, and the existence of a rapidly utilized photosynthetically produced substrate. Correlative relationships between bacterial parameters with chlorophyll a were significant during stratified hydrography, but diminished or became non-significant during destratified hydrography. Estimates of microzooplankton grazing rates upon bacteria decreased significantly during the onset of destratification. During the stratified hydrography, bacterial parameters displayed highly significant negative correlations to ammonium, however these relationships disappeared during the destratified hydrography. Results of this study indicate that destratification changes the trophic interactions of bacteria within the microbial loop, however these changes are not necessarily reflected by temporal patterns of bacterial abundance

Classification and identification of Pfiesteria and Pfiesteria-like species

Dinoflagellates can be classified both botanically and zoologically; however, they are typically put in the botanical division Pyrrhophyta. As a group they appear most related to the protistan ciliates and apicomplexans at the ultrastructure level. Within the Pyrrhophyta are both unarmored and armored forms of the dominant, motile flagellated stage. Unarmored dinoflagellates do not have thecal or wall plates arranged in specific series, whereas armored species have plates that vary in thickness but are specific in number and arrangement. In armored dinoflagellates, the plate pattern and tabulation is a diagnostic character at the family, subfamily, and even genus levels. In most cases, the molecular characterization of dinoflagellates confirms the taxonomy on the basis of external morphology; this has been demonstrated for several groups. Together, both genetic and morphological criteria are becoming increasingly important for the characterization, separation, and identification of dinoflagellates species. Pfiesteria and Pfiesteria-like species are thinly armored forms with motile dinospore stages characterized by their distinct plate formulae. Pfiesteria piscicida is the best-known member of the genus; however, there is at least one other species. Other genetically and morphologically related genera, now grouped under the common names of Lucy, Shepherd\u27s crook, and cryptoperidiniopsoid, are being studied and described in separate works. All these other heterotrophic dinoflagellate groups, many of which are thought to be benign, co-occur in estuarine waters where Pfiesteria has been found

Spectral differences and temporal stability of phycoerythrin fluorescence in estuarine and coastal waters due to the domination of labile cryptophytes and stabile cyanobacteria

Laser fluorosensing and epifluorescence microscopy were used jointly to identify the origin of different spectral peaks of phycoerythrin in estuarine and coastal samples. The fluorescence of the samples was also examined as a function of the time elapsed after a water circulation system was turned on. Coastal samples were dominated by cyanobacteria and exhibited a constant phycoerythrin fluorescence with time. The phycoerythrin fluorescence of the Chesapeake Bay estuarine samples first increased strongly, reached a maximum, and then decreased to below the original level; these samples were dominated by cryptophytes which epifluorescence techniques revealed were being destroyed by the circulation system. A simple mathematical model was developed to describe the effects of cell disruption, the uncoupling of energy transfer between pigments, and the subsequent breakdown of the solubilized phycoerythrin

Are Pfiesteria species toxicogenic? Evidence against production of ichthyotoxins by Pfiesteria shumwayae

The estuarine genus Pfiesteria has received considerable attention since it was first identified and proposed to be the causative agent of fish kills along the mid-Atlantic coast in 1992. The presumption has been that the mechanism of fish death is by release of one or more toxins by the dinoflagellate. In this report, we challenge the notion that Pfiesteria species produce ichthyotoxins. Specifically, we show that (i) simple centrifugation, with and without ultrasonication, is sufficient to detoxify water of actively fish-killing cultures of Pfiesteria shumwayae, (ii) organic extracts of lyophilized cultures are not toxic to fish, (fit) degenerate primers that amplify PKS genes from several polyketide-producing dinoflagellates failed to yield a product with A shumwayae DNA or cDNA, and (iv) degenerate primers for NRPS genes failed to amplify any NRPS genes but (unexpectedly) yielded a band (among several) that corresponded to known or putative PKSs and fatty acid synthases. We conclude that P. shumwayae is able to kill fish by means other than releasing a toxin into bulk water. Alternative explanations of the effects attributed to Pfiesteria are suggested

On the conservation of the slow conformational dynamics within the amino acid kinase family: NAGK the paradigm

N-Acetyl-L-Glutamate Kinase (NAGK) is the structural paradigm for examining the catalytic mechanisms and dynamics of amino acid kinase family members. Given that the slow conformational dynamics of the NAGK (at the microseconds time scale or slower) may be rate-limiting, it is of importance to assess the mechanisms of the most cooperative modes of motion intrinsically accessible to this enzyme. Here, we present the results from normal mode analysis using an elastic network model representation, which shows that the conformational mechanisms for substrate binding by NAGK strongly correlate with the intrinsic dynamics of the enzyme in the unbound form. We further analyzed the potential mechanisms of allosteric signalling within NAGK using a Markov model for network communication. Comparative analysis of the dynamics of family members strongly suggests that the low-frequency modes of motion and the associated intramolecular couplings that establish signal transduction are highly conserved among family members, in support of the paradigm sequence→structure→dynamics→function © 2010 Marcos et al

Results from evaluations of models and cost-effectiveness tools to support introduction decisions for new vaccines need critical appraisal

The World Health Organization (WHO) recommends that the cost-effectiveness (CE) of introducing new vaccines be considered before such a programme is implemented. However, in low- and middle-income countries (LMICs), it is often challenging to perform and interpret the results of model-based economic appraisals of vaccines that benefit from locally relevant data. As a result, WHO embarked on a series of consultations to assess economic analytical tools to support vaccine introduction decisions for pneumococcal, rotavirus and human papillomavirus vaccines. The objectives of these assessments are to provide decision makers with a menu of existing CE tools for vaccines and their characteristics rather than to endorse the use of a single tool. The outcome will provide policy makers in LMICs with information about the feasibility of applying these models to inform their own decision making. We argue that if models and CE analyses are used to inform decisions, they ought to be critically appraised beforehand, including a transparent evaluation of their structure, assumptions and data sources (in isolation or in comparison to similar tools), so that decision makers can use them while being fully aware of their robustness and limitations