Zoogloea caeni sp. nov., a floc-forming bacterium isolated from activated sludge

1 Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea 2 Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju 660-701, Republic of Korea 3 Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-701, Republic of Korea 4 Department of Animal Science and Technology, Sunchon National University, Sunchon 540-742, Republic of Korea Correspondence Che Ok Jeon cojeon{at}cau.ac.kr Two floc-forming, nitrogen-fixing bacteria, strains EMB43 T and EMB61, obtained from activated sludge of a domestic wastewater treatment plant in Korea, were characterized. The two strains were very closely related, sharing 99.7 % 16S rRNA gene sequence similarity and showing a level of DNA–DNA relatedness of 93 %, which suggests that they represent members of a single species. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two novel isolates formed a distinct phyletic lineage within the genus Zoogloea and were related most closely to Zoogloea resiniphila DhA-35 T and Zoogloea oryzae A-7 T , with sequence similarities of 97.2 %. Levels of DNA–DNA relatedness between strain EMB43 T and Z. resiniphila DhA-35 T and Z. oryzae A-7 T were 12.8 and 7.4 %, respectively. Cells of strains EMB43 T and EMB61 were facultatively aerobic, rod-shaped, Gram-negative and motile by means of a polar flagellum. The strains grew at temperatures of 15–40 °C (optimum: 25–30 °C) and at pH 6.0–9.0 (optimum: pH 6.5–7.5). The predominant fatty acids were C 16 : 0 , C 10 : 0 3-OH and summed feature 3 (C 16 : 1 7 c and/or iso-C 15 : 0 2-OH), and the predominant polar lipid was phosphatidylethanolamine. The genomic DNA G+C content was 64.9–65.0 mol% and the major isoprenoid quinone was ubiquinone-8 (Q-8). On the basis of phenotypic, chemotaxonomic and molecular data, the isolates are considered to represent a novel species of the genus Zoogloea , for which the name Zoogloea caeni sp. nov. is proposed. The type strain is EMB43 T (=KCTC 22084 T =DSM 19389 T ). The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of strains EMB43 T and EMB61 are DQ413148 and DQ413150 , respectively. A transmission electron micrograph showing the general morphology of negatively stained cells of strain EMB43 T , and a table detailing the cellular fatty acid compositions of strains EMB43 T and EMB61 and related species are available with the online version of this paper.