Alga-lytic activity of Pseudomonas fluorescens against the red tide causing marine alga Heterosigma akashiwo (Raphidophyceae)

Abstract

Abstract A bacterial strain, HAK-13, exhibited strongest activity against Heterosigma akashiwo and was capable of controlling this bloom forming phytoplankton. Based on 16S rDNA sequences and biochemical and morphological characteristics, the strain HAK-13 was determined to be Pseudomonas fluorescens on the basis of 99.9% similarity with reference strains in the DNA databases. The growth of H . akashiwo was strongly suppressed by HAK-13 in all growth phases, with the strongest alga-lytic activity noted against harmful bloom-forming species in the exponential stage (6–22 days). Host range tests showed that HAK-13 also significantly inhibited the growth of Alexandrium tamarense and Cochlodinium polykrikoides but could not destroy Gymnodinium catenatum . P. fluorescens HAK-13 indirectly attacked H . akashiwo by alga-lytic substances that might be located at the compartment of cytoplasmic membrane of the bacterium at a level of 45.86 units/mg of specific activity. The results indicated that P . fluorescens HAK-13 caused cell lysis and death of H . akashiwo , A . tamarense , and C . polykrikoides dramatically and Prorocentrum dentatum slightly. Therefore, P . fluorescens HAK-13 has potential for use as a selective biocontrol of harmful algal blooms.