Importance of Photosynthetic Sulfur Bacteria, Chromatium sp. as an Organic Matter Producer in Lake Kaiike

Abstract

The purpose of the present paper is to show the importance of photosynthetic sulfur bacteria, Chromatium sp., as an organic matter producer in Lake Kaiike, a small lake situated on the north coast of Kamikoshiki Island. The lake (surface area : 0.15 km2, maximum depth : 11.6 m) waters are brackish above and very saline below. The deeper part of the saline water contains a remarkable amount of hydrogen sulfide. Water at the O2-H2S boundary contains a dense population of Chromatium sp. The bacteria concentration attains a maximum of 5.3 106 cells/ml, forming the so-called “bacterial plate.” The carbon assimilation rate at the boundary reaches 30-80 % of the total one. A large number of zooplankton such as Brachionus sp. and Tintinnopsis sp. inhabit the water above the bacterial plate. Chromatium sp. appears to have an important role as a food source in supporting the high zooplankton biomass in Lake Kaiike.