Dense mats of thioploca, gliding filamentous sulfur-oxidizing bacteria in lake Biwa, central Japan

Dense mats of Thioploca spp., gliding filamentous sulfur-oxidizing bacteria were first found in Japan in the sediments of the profundal areas of Lake Biwa, the largest lake in Japan. Thioploca spp. were widely distributed in the northern basin of Lake Biwa and were morphologically similar to Thioploca ingrica. The biomass of Thioploca was estimated and compared between the upper (0–2 cm) and the lower (deeper than 2 cm) layer sediments of three profundal stations. It was one to two orders of magnitude larger in the upper layer for all stations. Upper layer biomass was also compared among five stations of different depths from 3 to 90 m deep, and the most dense trichomes, 5.4 m per cm2 exhibited as total trichome length, were observed at the profundal station of 90 m deep, larger by three orders of magnitude than in the shallow stations. Several facts indicate that Thioploca has recently increased on the profundal bottoms of the lake.