Specificity Re-evaluation of Oligonucleotide Probes for the Detection of Marine Picoplankton by Tyramide Signal Amplification-Fluorescent Hybridization.

Oligonucleotide probes are increasingly being used to characterize natural microbial assemblages by Tyramide Signal Amplification-Fluorescent Hybridization (TSA-FISH, or CAtalysed Reporter Deposition CARD-FISH). In view of the fast-growing rRNA databases, we re-evaluated the specificity of eleven bacterial and eukaryotic probes and competitor frequently used for the quantification of marine picoplankton. We performed tests on cell cultures to decrease the risk for non-specific hybridization, before they are used on environmental samples.

Fluorescence in situ hybridization of Microcystis strains producing microcystin using specific mRNA probes.

Unlabelled: Cyanobacteria are ubiquitous micro-organisms that can produce toxic compounds, the cyanotoxins. The monitoring of such producers in the environment is of prime importance for human health. An attractive technology for such monitoring is fluorescence in situ hybridization (FISH), which allows the detection and enumeration of environmental micro-organisms.

Importance of N2-Fixation on the Productivity at the North-Western Azores Current/Front System, and the Abundance of Diazotrophic Unicellular Cyanobacteria.

To understand the impact of the northwestern Azores Current Front (NW-AzC/AzF) system on HCO3--and N2-fixation activities and unicellular diazotrophic cyanobacteria (UCYN) distribution, we combined geochemical and biological approaches from the oligotrophic surface to upper mesopelagic waters. N2-fixation was observed to sustain 45-85% of the HCO3--fixation in the picoplanktonic fraction performing 47% of the total C-fixation at the deep chlorophyll maximum north and south of the AzF. N2-fixation rates as high as 10.

Quantitative assessment of picoeukaryotes in the natural environment by using taxon-specific oligonucleotide probes in association with tyramide signal amplification-fluorescence in situ hybridization and flow cytometry.

Picoeukaryotes (cells of <3 micro m in diameter) contribute significantly to marine plankton biomass and productivity, and recently molecular studies have brought to light their wide diversity. Among the methods that have been used so far to quantify aquatic microorganisms, fluorescence in situ hybridization of oligonucleotide probes combined with flow cytometry offers the advantages of both high resolution for taxonomic identification and automated cell counting. However, cell losses, cell clumps, and low signal-to-background ratio have often been mentioned as major problems for routine application of this combination of techniques.