Cyanobium is a genus of picoprokaryotic cyanophytes, which includes species worldwide. The present study investigated the morphology, ultrastructure, and molecular phylogeny of the unrecorded genus Cyanobium Rippka & Cohen-Bazire 1983 and species Cyanobium gracile Rippka & Cohen-Bazire 1983. A C. gracile culture from a freshwater sample collected from the Adongji pond was established by singlecell isolation. Morphological data were analyzed using light and transmission electron microscopy. C. gracile lives as solitary cells without gelatinous envelopes and is ovate, oval, or shortly rod-shaped. Thylakoids are laid along the cell walls, with three thylakoid membranes parallel to each other. Nucleoplasm was observed in the center of the cell. Molecular phylogeny performed with data from 16S small subunit ribosomal DNA gene (SSU rDNA) sequences showed that the three strains of C. gracile, including the type strain (PCC6307) and a newly recorded strain (Adong101619), formed a distinct clade with a high supporting value (maximum-likelihood=100, pp=1.00). Based on morphology and molecular data, we report the newly recorded C. gracile in Korea.

Abstract
INTRODUCTION
MATERIALS AND METHODS
    1. Sampling and clonal culture of Cyanobiumgracile
    2. Light microscopy
    3. Transmission electron microscopy
    4. DNA extraction, amplification, andsequencing
    5. Phylogenetic analyses
RESULTS AND DISCUSSION
    1. Taxonomic summary
    2. Morphology and ultrastructure
    3. Phylogeny
REFERENCES

• Dae Ryul Kwon(Nakdonggang National Institute of Biological Resources)
• Bok Yeon Jo(Nakdonggang National Institute of Biological Resources)
• Seok Won Jang(Nakdonggang National Institute of Biological Resources)
• Chang Soo Lee(Nakdonggang National Institute of Biological Resources)
• Seung Won Nam(Nakdonggang National Institute of Biological Resources) Corresponding author