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

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_16:1ω7c 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).