Formation of Single Cell Detritus Densely Covered with Bacteria during Experimental Degradation of Laminaria japonica Thalli

Abstract

The degrading process of Laminaria japonica thalli by a marine bacterium, Alteromonas sp. strain AR06, was examined by 4,6'-diamidino-2-phenylindole (DAPI) stain and epifluorescence microscopy. The surfaces of the thalli particles were densely covered with the bacterial cells within 24 hours of contact and for over 15 days thereafter. A portion of the algal cells was completely fragmented to single cells by the bacterium in a few days. Each single cell detritus (SCD) particle initially contained cytoplasmic material or structure, ca. 6 μm in diameter, as a core, but lost it as a result of bacterial decomposition. These observations were confirmed by the time course change of the particle size distribution, which showed the accumulation of one cell-size particles of around 4-10 μmi in diameter. The bacterium could grow on the surface of alginate beads, suggesting possible contribution of this material to the bacterial attachment observed on the thalli. The bacterium was identified as Alteromonas espejiana, an alginate decomposer, according to Bergey's manual of systematic bacteriology. The formation of the single cell detritus may help link the primary production by macroalgae and the secondary production of suspension feeders in algal vegetating areas.