Rapid quantification of the toxic alga Prymnesium parvum in natural samples by use of a specific monoclonal antibody and solid-phase cytometry

Synthesis of glyceryl glycosides related to A-type prymnesin toxins

A suite of glycosylated glycerol derivatives representing various fragments of the glycosylated ichthyotoxins called prymnesins were chemically synthesised. Glycerol was used to represent a small fragment of the prymnesin backbone, and was glycosylated at the 2° position with the sugars currently reported to be present on prymnesin toxins. Neighbouring group participation was utilised to synthesise 1,2-trans-glycosides. SnCl2-promoted glycosylation with furanosyl fluorides gave 1,2-cis-furanosides with moderate stereocontrol, whilst TMSOTf promoted glycosylation with a furanosyl imidate gave a 1,2-cis-furanoside with good stereocontrol. The chemical synthesis of two larger glyceryl diglycoside fragments of prymnesin-1, glycosylated with α-ʟ-arabinopyranose and α-ᴅ-ribofuranose, is also described. As the stereochemistry of the prymnesin backbones at this region is undefined, both the 2R- and 2S- glycerol isomers were synthesised. The separated diastereoisomers were distinguished by comparing NOESY NMR with computational models.

Molecular Techniques for the Detection of Organisms in Aquatic Environments, with Emphasis on Harmful Algal Bloom Species

Molecular techniques to detect organisms in aquatic ecosystems are being gradually considered as an attractive alternative to standard laboratory methods. They offer faster and more accurate means of detecting and monitoring species, with respect to their traditional homologues based on culture and microscopic counting. Molecular techniques are particularly attractive when multiple species need to be detected and/or are in very low abundance. This paper reviews molecular techniques based on whole cells, such as microscope-based enumeration and Fluorescence In-Situ Hybridization (FISH) and molecular cell-free formats, such as sandwich hybridization assay (SHA), biosensors, microarrays, quantitative polymerase chain reaction (qPCR) and real time PCR (RT-PCR). Those that combine one or several laboratory functions into a single integrated system (lab-on-a-chip) and techniques that generate a much higher throughput data, such as next-generation systems (NGS), were also reviewed. We also included some other approaches that enhance the performance of molecular techniques. For instance, nano-bioengineered probes and platforms, pre-concentration and magnetic separation systems, and solid-phase hybridization offer highly pre-concentration capabilities. Isothermal amplification and hybridization chain reaction (HCR) improve hybridization and amplification techniques. Finally, we presented a study case of field remote sensing of harmful algal blooms (HABs), the only example of real time monitoring, and close the discussion with future directions and concluding remarks.

Quantitative assessment of toxic and nontoxic Microcystis colonies in natural environments using fluorescence in situ hybridization and flow cytometry

Toxic cyanobacterial blooms constitute a threat to human safety because Microcystis sp. releases microcystins during growth, and particularly during cell death. Therefore, analysis of toxic and nontoxic Microcystis in natural communities is required in order to assess and predict bloom dynamics and toxin production by these organisms. In this study, an analysis combining fluorescence in situ hybridization (FISH) with flow cytometry (FCM) was used to discriminate between toxic and nontoxic Microcystis and also to quantify the percentage of toxic Microcystis present in blooms. The results demonstrate that the combination of FISH and flow cytometry is a useful approach for studying the ecology of Microcystis toxin production and for providing an early warning for toxic Microcystis blooms.

Prymnesins: toxic metabolites of the golden alga, Prymnesium parvum Carter (Haptophyta)

Increasingly over the past century, seasonal fish kills associated with toxic blooms of Prymnesium parvum have devastated aquaculture and native fish, shellfish, and mollusk populations worldwide. Protracted blooms of P. parvum can result in major disturbances to the local ecology and extensive monetary losses. Toxicity of this alga is attributed to a collection of compounds known as prymnesins, which exhibit potent cytotoxic, hemolytic, neurotoxic and ichthyotoxic effects. These secondary metabolites are especially damaging to gill-breathing organisms and they are believed to interact directly with plasma membranes, compromising integrity by permitting ion leakage. Several factors appear to function in the activation and potency of prymnesins including salinity, pH, ion availability, and growth phase. Prymnesins may function as defense compounds to prevent herbivory and some investigations suggest that they have allelopathic roles. Since the last extensive review was published, two prymnesins have been chemically characterized and ongoing investigations are aimed at the purification and analysis of numerous other toxic metabolites from this alga. More information is needed to unravel the mechanisms of prymnesin synthesis and the significance of these metabolites. Such work should greatly improve our limited understanding of the physiology and biochemistry of P. parvum and how to mitigate its blooms.

Immunofluorescence flow cytometry technique for enumeration of the brown-tide alga, Aureococcus anophagefferens

A new immunologically based flow cytometry (IFCM) technique was developed to enumerate Aureococcus anophagefferens, a small pelagophyte alga that is the cause of "brown tides" in bays and estuaries of the mid-Atlantic states along the U.S. coast. The method utilizes a monoclonal antibody conjugated to fluorescein isothiocyanate (FITC-MAb) to label the surface of A. anophagefferens cells which are then detected and enumerated by using a flow cytometer. Optimal conditions for FITC-MAb staining, including solution composition, incubation times, and FITC-MAb concentrations, were determined. The FITC-MAb method was tested for cross-reactivity with nontarget, similarly sized, photoautotrophic protists, and the method was compared to an enzyme-linked immunosorbent assay (ELISA) using the same MAb. Comparisons of the IFCM technique to traditional microscopy enumeration of cultures and spiked environmental samples showed consistent agreement over several orders of magnitude (r(2) > 0.99). Comparisons of the IFCM and ELISA techniques for enumerating cells from a predation experiment showed a substantial overestimation (up to 10 times higher) of the ELISA in the presence of consumers of A. anophagefferens, presumably due to egested cell fragments that retained antigenicity, using the ELISA method, but were not characterized as whole algal cells by the IFCM method. Application of the IFCM method to environmental "brown-tide" samples taken from the coastal bays of Maryland demonstrated its efficacy in resolving A. anophagefferens abundance levels throughout the course of a bloom and over a large range of abundance values. IFCM counts of the brown-tide alga from natural samples were consistently lower than those obtained using the ELISA method and were equivalent to those of the polyclonal immunofluorescence microscopy technique, since both methods discriminate intact cells. Overall, the IFCM approach was an accurate and relatively simple technique for the rapid enumeration of A. anophagefferens in natural samples over a wide range of abundance values (10(3) to 10(6) cells ml(-1)).

Picoeukaryotic sequences in the Sargasso sea metagenome

Many sequences from picoeukaryotes were found in DNA sequence data assembled from Sargasso seawater.

Background

With genome sequencing becoming more and more affordable, environmental shotgun sequencing of the microorganisms present in an environment generates a challenging amount of sequence data for the scientific community. These sequence data enable the diversity of the microbial world and the metabolic pathways within an environment to be investigated, a previously unthinkable achievement when using traditional approaches. DNA sequence data assembled from extracts of 0.8 μm filtered Sargasso seawater unveiled an unprecedented glimpse of marine prokaryotic diversity and gene content. Serendipitously, many sequences representing picoeukaryotes (cell size <2 μm) were also present within this dataset. We investigated the picoeukaryotic diversity of this database by searching sequences containing homologs of eight nuclear anchor genes that are well conserved throughout the eukaryotic lineage, as well as one chloroplastic and one mitochondrial gene.

Results

We found up to 41 distinct eukaryotic scaffolds, with a broad phylogenetic spread on the eukaryotic tree of life. The average eukaryotic scaffold size is 2,909 bp, with one gap every 1,253 bp. Strikingly, the AT frequency of the eukaryotic sequences (51.4%) is significantly lower than the average AT frequency of the metagenome (61.4%). This represents 4% to 18% of the estimated prokaryotic diversity, depending on the average prokaryotic versus eukaryotic genome size ratio.

Conclusion

Despite similar cell size, eukaryotic sequences of the Sargasso Sea metagenome have higher GC content, suggesting that different environmental pressures affect the evolution of their base composition.

Detection and quantification of Prymnesium parvum (Haptophyceae) by real-time PCR

AIMS

The ichthyotoxic species Prymnesium parvum (Haptophyceae) is difficult to quantify in a microscopy-based monitoring programme, because the cells are very small, fragile and their morphology can be distorted by the use of fixatives. In the attempt to overcome these problems, a real-time PCR-based method for the rapid and sensitive identification and quantification of P. parvum was developed.

METHODS AND RESULTS

A quantitative real-time PCR assay was optimized with primers designed on the internal transcribed spacer 2 rDNA region of P. parvum. This PCR assay was specific, showing no amplification of DNA extracted from closely related species, and sensitive. Moreover, this method was able to detect and reliably quantify P. parvum cells in preserved environmental samples artificially spiked with known amounts of cultured cells.

CONCLUSIONS

Considering the specificity, sensitivity and applicability to preserved environmental samples, this method may be a useful tool for the monitoring of this toxic species.

SIGNIFICANCE AND IMPACT OF THE STUDY

The real-time PCR method described in this study may represent a progress towards the rapid detection and quantification of P. parvum cells in water-monitoring programmes, allowing the early application of strategies to control bloom events, such as the use of clay minerals.

Carbon-isotopic analysis of microbial cells sorted by flow cytometry

One of the outstanding current problems in both geobiology and environmental microbiology is the quantitative analysis of in situ microbial metabolic activities. Techniques capable of such analysis would have wide application, from quantifying natural rates of biogeochemical cycling to identifying the metabolic activity of uncultured organisms. We describe here a method that represents one step towards that goal, namely the high-precision measurement of ¹³ C in specific populations of microbial cells that are purified by fluorescence-activated cell sorting (FACS). Sorted cells are concentrated on a Teflon membrane filter, and their ¹³ C content is measured by coupling an isotope ratio mass spectrometer (IRMS) with a home-built spooling wire microcombustion (SWiM) apparatus. The combined instrumentation provides measurements of δ¹³ C in whole cells with precision better than 0.2‰ for samples containing as little as 25 ng of carbon. When losses associated with sample handling are taken into account, isotopic analyses require sorting roughly 10⁴ eukaryotic or 10⁷ bacterial cells per sample. Coupled with ¹³ C-labelled substrate additions, this approach has the potential to directly quantify uptake of metabolites in specific populations of sorted cells. The high precision afforded by SWiM-IRMS also permits useful studies of natural abundance variations in ¹³ C. The approach is equally applicable to specific populations of cells sorted from multicellular organisms.

Fountain Flow cytometry, a new technique for the rapid detection and enumeration of microorganisms in aqueous samples

BACKGROUND

Pathogenic microorganisms are known to cause widespread waterborne disease worldwide. There is an urgent need to develop a technique for the real-time detection of pathogens in environmental samples at low concentrations, <10 microorganisms/ml, in large sample volumes, > or =100 ml.

METHODS

A novel method, Fountain Flowtrade mark cytometry, for the rapid and sensitive detection of individual microorganisms in aqueous samples is presented. Each sample is first incubated with a fluorescent label and then passed as a stream in front of a laser, which excites the label. The fluorescence is detected with a CCD imager as the sample flows toward the imager along its optical axis. The feasibility of Fountain Flow cytometry (FFC) is demonstrated by the detection of Escherichia coli labeled with ChemChrome CV6 and SYBR Gold in buffer and natural river water.

RESULTS

Detections of labeled E. coli were made in aqueous suspensions with an efficiency of 96% +/- 14% down to a concentration approximately 200 bacteria/ml.

CONCLUSIONS

The feasibility of FFC is demonstrated by the detection of E. coli in buffer and natural river water. FFC should apply to the detection of a wide range of pathogenic microorganisms including amoebae.