Isolation and Identification of a Ca, Mg and Na-philic Bacterium Inhibiting the Growth of Red-Tide Plankton
Jaehak SOHN, Soyoung LEE, Junghyun LEE, and Sang-Jin KIM
Marine Microbiology Lab., Korea Ocean Research & Development Institute, Ansan P.O. Box. 29, Seoul 425-600, Korea
A bacterial strain showing an inhibitory activity against red-tide planktonic organisms was isolated from sea water in Masan Bay, southern coast of Korea, during red-tide bloom. This bacterial strain designated as OT-1 was motile, gram-negative rod and formed yellow colony on ZoBell 2216E agar medium. This strain showed oxidase-positive and flexirubin-negative reaction. According to the data of fatty acid analysis using MIDI system, strain OT-1 was found to be the nearest phylogenetic neighbor of Cytophaga johnsonae. Analysis of the 16S rRNA sequence by SIMILARITY-RANK program (version 2.5) of the Ribosomal Data Base (RDP) showed that the nearest phylogenetic neighbor of the strain OT-1 is C. latercula str. Lewin SIO-1 with S-ab value of 65.2%. According to these results, strain OT-1 was tentatively identified as Cytophaga sp.
This strain produced a substance which inhibited the growth of Cochlodinium polykrikoides, Heterosigma akashiwo, Skeletonema costatum and Thalassiosira sp. The inhibitory substance was heat stable and molecular weight of the substance was larger than 10 KDa. Strain OT- 1 was able to grow in distilled water supplemented with natural sea salt or in aged sea water. However, the strain was not able to grow in distilled water supplemented with chemically purified salt. Ca2+, Mg2+ and Na+ ions were found to be essential for the growth of the strain. Optimal NaC1 concentration was between 2 and 3% (w/v), and Km values for Ca2+ and Mg2+ ions estimated from the Lineweaver-Burk equation were about 0.1 mM. A bacterial strain which simultaneously requires Ca2+, Mg2+ and Na+ ions for the growth is firstly reported in this work and more physiological and biochemical characteristics are under study.
