Vertical Succession of Attached Bacteria and Its Relationship to the Distribution of Organic Matter in Seawater

Abstract

Vertical change of the heterotrophic bacterial community attached to particulate organic matter (POM) was studied in relation to the distribution of POM in the neritic sea of Japan. The analysis of bacterial community was performed by dividing the isolates into five groups: Vibrio (V), Pseudomonas-Alcaligenes (Ps), Acinetobacter-Moraxella (Ac), Chromogenic (C) and Gram-positive (Po) groups. The community structure of attached bacteria was quite different from that of free-living in the ambient seawater. In the water column, the community of attached bacteria showed the distinct vertical succession, which was: Ps→V→(Ps+Ac)→(Ac+C)→Ps. The attached bacteria in the layers where the decomposition of POM proceeded actively had high substrate-decomposing activity, whereas in the deeper layers with limited supply of the “fresh” POM the activity was low. These results suggest that the community of attached bacteria showed the vertical succession with the proceeding of POM decomposition from the community with a high biochemical activity to a low activity, as associated with the change of genera.