Characterization of marine bacteria and the activity of their enzyme systems involved in degradation of the algal storage glucan laminarin.

The algal storage glucan laminarin is one of the most abundant carbon sources for marine prokaryotes. Its degradation was investigated in bacteria isolated during and after a spring phytoplankton bloom in the coastal North Sea. On average, 13% of prokaryotes detected by epifluorescence counts were able to grow in Most Probable Number dilution series on laminarin as sole carbon source. Several bacterial strains were isolated from different dilutions, and phylogenetic characterization revealed that they belonged to different phylogenetic groups. The activity of the laminarin-degrading enzyme systems was further characterized in three strains of Vibrio sp. that were able to grow on laminarin as sole carbon source. At least two types of activity were detected upon degradation of laminarin: release of glucose, and release of glucans larger than glucose. The expression of laminarinase activity was dependent on the presence of the substrate, and was repressed by the presence of glucose. In addition, low levels of activity were expressed under starvation conditions. Laminarinase enzymes showed minimal activity on substrates with similar glucosidic bonds to those of laminarin, but different sizes and secondary and/or tertiary structures. The characteristics found in these enzyme systems may help to elucidate factors hampering rapid carbohydrate degradation by prokaryotes.

Chemical characterisation of three haemolytic compounds from the microalgal species Fibrocapsa japonica (Raphidophyceae).

The molecular structures of the three main haemolytic compounds (Fj1, Fj2 and Fj3) isolated from the ichthyotoxic microalgal species Fibrocapsa japonica have been investigated by NMR, LC-ESI-MS, ESI-MS-MS, IR, GC-MS and GC-HRMS methods. They are polyunsaturated fatty acids which we identified as: 6,9,12,15-octadecatetraenoic acid (OTA, C18:4omega3), 5,8,11,14,17-eicosapentaenoic acid (EPA, C20:5omega3) and 5,8,11,14-eicosatetraenoic acid (arachidonic acid AA, C20:4omega6). The identity of the latter two was confirmed on the basis of commercial standards (C20:5omega3 and C20:4omega6). Both displayed the same spectroscopic and chromatographic characteristics as Fj2 and Fj3 and had a similar strong haemolytic effect. We propose that when F. japonica cells accumulate in fish gills during blooms these compounds could be the cause of icthyotoxicity.