Algicidal bacteria isolated from the surface of seaweeds from the coast of Osaka Bay in the Seto Inland Sea, Japan

Abstract

Algicidal bacteria offer a promising tool for the prevention of red tides, because they are able to play a key role in terminating blooms in coastal areas. This study details the detection of vast numbers of algicidal bacteria attached to the surface of seaweeds such as Ulv a sp. and Gelidium sp. (of the order of 10⁶ cells g⁻¹ wet weight in some cases). Algicidal bacteria were isolated from Ulva sp. and Gelidium sp. from the coast of Osaka Bay from April to September 1999, and their algicidal properties were assessed using the prey microalgae Karenia mikimotoi, Heterosigma akashiwo, Fibrocapsa japonica and Chattonella antiqua. K. mikimotoi was the red tide species most susceptible to the algicidal bacteria isolated from seaweeds. Sequence analyses of the 16S rDNA gene revealed that these algicidal bacteria belonged to the genera Alteromonas, Pseudo-alteromonas, Vibrio, Cytophaga, Cellulophaga and Octadecabacter, and the family Rhodobacteraceae. Algicidal properties of five of 10 strains of bacteria isolated from seaweeds, belonging to the genera Alteromonas, Pseudoalteromonas and Cytophaga, have been previously reported in coastal red tide areas. It is therefore possible that seaweed beds play a significant role as providers of algicidal bacteria in preventing red tides to coastal waters.