Atsushi Mitsutani

Isolation and identification of the antialgal compound, harmane (1-methyl-β-carboline), produced by the algicidal bacterium, Pseudomonas sp. K44-1

Twelve strains of algicidal bacteria were isolated from the surfacewater of the pond Shinobazu and the moat Ote-bori (Tokyo, Japan). Nine of thesestrains were considered to be in the Pseudomonas group byanalyses of 16S rDNA sequences. The methanol extract ofPseudomonas sp. K44-1 showed marked antialgal activity bythe paper disk method. Harmane (1-methyl-β-carboline) was isolated fromtheethyl acetate extract of the whole culture broth ofPseudomonas sp. K44-1 by using silica gel columnchromatography and high performance liquid chromatography (HPLC). Harmaneshowedantagonistic activities against several cyanobacterial strains at aconcentration of 30 μg disk−1.

Analysis of algicidal proteins of a diatom-lytic marine bacterium Pseudoalteromonas sp. strain A25 by two-dimensional electrophoresis

Abstract A marine bacterium Pseudoalteromonas sp. strain A25 exhibits strong algicidal activity against diatoms. It could completely lyse the centric diatom Skeletonema costatum (Bacillariophyceae) NIES-324 within 2 days when inoculated at a density of 104 cells ml−1. Analysis of the cellular proteins of strain A25 and its algicidal activity-lacking mutant, A25W1, by two-dimensional (2-D) electrophoresis indicated that a large number of proteins were induced in the stationary phase cells of strain A25. These proteins were not detected in late-logarithmic phase cells of strain A25, nor in either the late-logarithmic or stationary phase cells of the mutant A25W1. Algicidal activity against S. costatum was also detected in cell-free extracts, but only in those from stationary phase cells of strain A25. These results suggest strongly that some of the proteins induced in the stationary phase contribute to the lysis of S. costatum by Pseudoalteromonas sp. strain A25.

Isolation of an algicidal marine bacterium with activity against the harmful dinoflagellate Heterocapsa circularisquama (Dinophyceae)

Abstract Red tides of a harmful dinoflagellate, Heterocapsa circularisquama, have caused mass mortality of bivalves such as oysters in western Japan since 1988. For the purpose of microbial control of the occurrence of these red tides, H. circularisquama-killing bacteria were screened. Although the frequency of H. circularisquama-killing microorganisms was low during the sampling period, a marine bacterium strain EHK-I, which had a strong algicidal activity against H. circularisquama, was isolated from the seawater of Etajima Bay, in the Seto Inland Sea of Japan. Strain EHK-1 killed H. circularisquama within 24 hours when the H. circularisquama culture in exponential phase was inoculated with this bacterium at a density of 1 × 105 cells ml−1. Strain EHK-1 lysed both the vegetative cells and temporary cysts of H. circularisquama. Strain EHK-1 is a novel algicidal bacterium according to 16S rRNA-based phylogenetic analysis.