2005 Volume 20 Issue 1 Pages 69-80
The layer of mucus on the surface of bluegills (Lepomis macrochirus) captured in Lake Biwa was characterized as 1) large enough to host microbes (ca. 76 μm thick), 2) a physically different environment from the surrounding lake water in viscosity and buffering capacity, and 3) chemically rich in organic substances, which may be utilized as nutrients. Based on DAPI staining and on the number of colonies formed respectively, it was found that ca. 103 times and 3 to 7 times the number of microbial cells were present in the mucus layer, as compared with the lake water. The bacterial flora of the mucus was greatly different from that of the lake water, according to a phylogenetic analysis. About 60% of the isolates from the mucus were Gram-positive. These Gram-positive isolates could be divided into two major groups. Each group consisted of strains sampled in one season, i.e., the strains sampled in July were closely related to the genus Staphylococcus, while the strains sampled in November were close to the genus Mycobacterium. In contrast, most isolates from the lake water were Gram-negative (72%); with all the strains closely related to β- and γ-Proteobacteria sampled in July. With the exception of one strain, the Gram-positive isolates from the lake water (6 strains) were all sampled in November. Almost all of the isolates from the mucus could metabolize glucose, whereas only half of the isolates from the lake water could do the same.
