An agar-degrading enzyme-producing strain was isolated from seawater. The isolate was identified as Microbulbifer sp. SD-1 by 16S rRNA sequencing analysis. The optimal pH and temperature for growth were 6.0 and 30°C, respectively, and growth was possible at pH 9.0 and 60°C. The isolate required 5% NaCl for optimal growth and showed 45% growth activity without NaCl. Agar concentrations of 0-0.4% in the medium did not affect growth. Thin-layer chromatography analysis revealed that this strain could degrade agar into a monosaccharide and oligosaccharide, which may have industrial applications.

Takifugu rubripes is more expensive than other species of the genus because of its high protein content and special flavor. However, it is easily confused with imported T. chinensis and T. pseudommus because they have similar morphological characteristics. We identified single nucleotide polymorphism (SNP) markers of T. rubripes by genotyping-by-sequencing (GBS) and evaluated their ability to distinguish among T. rubripes, T. chinensis, and T. pseudommus. In all, 18 polymorphic SNPs were subjected to phylogenetic analyses of the three Takifugu species. Additionally, we subjected a second set of samples to Sanger sequencing to verify that the polymorphic SNPs could be used to evaluate the genetic variation among the three Takifugu species. A phylogenetic tree that included the analyzed sequence of set A, which is referred to as the reference sequence, and a validation sequence of set B with 18 SNPs were produced. Based on this phylogenetic tree and STRUCTURE analyses, T. rubripes, T. chinensis and T. pseudommus have low genetic variation and should be considered the same gene pool. Our findings suggest that further studies are needed to estimate the genetic association of the three Takifugu species.

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