Seasonal Change of Bacterial Community Structure in a Biofilm Formed on the Surface of the Aquatic Macrophyte Phragmites australis

The seasonal change of bacterial community structure in biofilms on the surface of reed (Phragmites australis) was investigated for about three years (from 2005 June to 2008 March) in Lake Biwa by comparing it with that in surrounding lake water. The community structure in biofilms was different from that in the lake water throughout the seasons and years. The community structure in lake water was similar in the same seasons of different years, corresponding to similar environmental factors (i.e., temperature, dissolved oxygen, and light intensity) and nutrient ion concentrations at the same season. However, the community structure in the biofilms was not similar in the same season of different years. This seems to be due to the formation of new biofilms on sprouted reeds in every early summer and the high nutrient concentrations and bacterial density in subsequently formed biofilms. Although the community structure in the biofilms changed along with the seasonal change, the bacteria belonging to Bacillus and Paenibacillus were detected in any season. This study revealed the possibility that the bacterial community structure in the initial stage of the biofilm formation govern the subsequent seasonal change of the community structure in biofilms.