ミズワタクチビルケイソウCymbella janischii の近畿地方からの初記録およびその生細胞の形態観察

抄録

We report the occurrence of Cymbella janischii in Ado River flowing into the Lake Biwa in 2022; this is the first report of this diatom from Kinki Area, Japan. Cymbella janischii has been known as an endemic species in the Pacific Northwest of North America. In Japan, however, it has become known as an invasive species. It is likely that it was introduced from the native locality into Kyushu in 2006 or shortly before, and has rapidly spread throughout Japanese rivers. In Ado River, it formed massive colonies on rocks by means of mucilage stalks secreted from one end of the cells, but the colony scattered only on the river bed. The cell had a dorsiventral outline, with an intricately shaped plastid. Fluorescence microscopy on living cells stained with SYBR Green and fluorescence-labeled lectin revealed that the position of the nucleus was appressed to the ventral side, and polysaccharide covered the entire frustule as well as the mucilage stalks. We also confirmed the identity of the species with the sequence of the 18S ribosomal RNA gene.