Roel Pel

Improved fatty acid detection in micro-algae and aquatic meiofauna species using a direct thermal desorption interface combined with comprehensive gas chromatography–time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography (GC x GC) with time-of-flight mass spectrometry detection is used to profile the fatty acid composition of whole/intact aquatic microorganisms such as the common fresh water green algae Scenedesmus acutus and the filamentous cyanobacterium Limnothrix sp. strain MRI without any sample preparation steps. It is shown that the technique can be useful in the identification of lipid markers in food-web as well as environmental studies. For instance, new mono- and diunsaturated fatty acids were found in the C(16) and C(18) regions of the green algae S. acutus and the filamentous cyanobacterium Limnothrix sp. strain MRI samples. These fatty acids have not, to our knowledge, been detected in the conventional one-dimensional (1D) GC analysis of these species due to either co-elution and/or their presence in low amounts in the sample matrix. In GC x GC, all congeners of the fatty acids in these microorganisms could be detected and identified due to the increased analyte detectability and ordered structures in the two-dimensional separation space. The combination of direct thermal desorption (DTD)-GC x GC-time-of-flight mass spectrometry (ToF-MS) promises to be an excellent tool for a more accurate profiling of biological samples and can therefore be very useful in lipid biomarker research as well as food-web and ecological studies.

LINKING FLOW CYTOMETRIC CELL SORTING AND COMPOUND‐SPECIFIC 13C‐ANALYSIS TO DETERMINE POPULATION‐SPECIFIC ISOTOPIC SIGNATURES AND GROWTH RATES IN CYANOBACTERIA‐DOMINATED LAKE PLANKTON1

A novel methodology was applied to determine the δ13C signatures of natural cyanobacterial and algal populations by combined compound‐specific isotope ratio mass spectrometry and pyrolytic methylation‐gas chromatography (Py‐GC‐IRMS) of the fatty acids released from phytoplankton fractions collected using fluorescence‐activated cell sorting. Py‐GC‐IRMS provided direct analysis of the very small samples (<200 ng total C) derived from the cell sorting of individual phototrophic populations, while minimizing the chances on contamination and loss in sample handling. Despite trichome lengths exceeding the diameter of the sort droplets, filamentous cyanobacteria were amenable to population‐specific cell sorting. In concert with 13C‐CO2 labeling, the combined use of flow cytometric cell sorting and Py‐GC‐IRMS enabled both the assessment of standing stocks and of population‐specific growth rates of the predominant cyanobacterial and algal taxa in Lake Loosdrecht (The Netherlands). Filamentous prochlorophytes, formerly the dominant cyanobacterial taxon in the lake, appeared less abundant in recent years and exhibited growth rates 30%–40% lower than the rates recorded for oscillatorioid populations. Diatom and green algal populations grew at rates 4‐ to 10‐fold higher than filamentous cyanobacteria and are thus important for the lakes carbon budget. This approach offers new possibilities in studying plankton dynamics at a resolution not feasible in the past.

Observations on cyanobacterial population collapse in eutrophic lake water.

In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted . The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and >100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host–cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes.

ARCHITECTURE AND CHEMICAL-COMPOSITION OF THE MAGNETITE-BEARING LAYER IN THE RADULA TEETH OF CHITON-OLIVACEUS (POLYPLACOPHORA)

The radula apparatus in chitons (Polyplacophora) is a toothed ribbon used to excavate algae living on and in rocky substrates. Magnetite (Fe3O4) is a component of mineralized radula teeth. It is contained in a layer beneath the surface that leads in the cutting direction. The architecture and composition of this layer in fully mineralized teeth of Chiton olivaceus were studied by scanning electron microscopy. Worn, broken, sectioned, and etched teeth were examined. Etching was done with 4N HCl or by incubating teeth in cultures of bacteria that exclusively used chitin as a source of carbon and energy.

MYC expression and translocation analyses in low-grade and transformed Follicular Lymphoma

Low‐grade follicular lymphoma (FL) (grade 1/2, FL1/2) has an annual risk of transformation of ≈3%, which is associated with aberrations in CDKN2A/B, TP53, and MYC. As in diffuse large B‐cell lymphoma, high MYC expression in transformed FL (tFL) might predict a MYC breakpoint.

Chitinolytic Communities From an Anaerobic Estuarine Environment

Mineralization of organic matter in anaerobic environments is accomplished by a community of physiologically different bacteria.1 Biogenic polymers such as carbohydrates and proteins are hydrolyzed and the monomers produced are subsequently converted to a variety of products by fermentative bacteria. Their fermentation products are further oxidized by sulfate-reducing bacteria or by syntrophic consortia of acetogenic and methanogenic bacteria. Our knowledge of anaerobic polysaccharide degrading communities mainly originates from the cellulolytic system in the rumen2,3,4 Much less is known about the microbiology of anaerobic polysaccharide composition in marine environments. This is particularly true for the structure of these communities and the possible interspecies interaction involved (i.e. the primary hydrolysing bacteria and those using hydrolysis and fermentation products).