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Azonexus hydrophilus sp. nov., a nifH gene-harbouring bacterium isolated from freshwater

¹ Department of Soil and Environmental Sciences, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan
² Laboratory of Microbiology, Department of Seafood Science, National Kaohsiung Marine University, No. 142, Hai-Chuan Rd, Nan-Tzu, Kaohsiung City 811, Taiwan
³ Division of Biology and Ocean Sciences, Inha University, Yonghyun Dong, Incheon 402-751, Republic of Korea

Correspondence
Wen-Ming Chen
p62365{at}ms28.hinet.net

Three Gram-negative, non-pigmented, rod-shaped, facultatively aerobic bacterial strains, designated d8-1^T, d8-2 and IMCC1716, were isolated from a freshwater spring sample and a eutrophic freshwater pond. Based on characterization using a polyphasic approach, the three strains showed highly similar phenotypic, physiological and genetic characteristics. All of the strains harboured the nitrogenase gene nifH, but nitrogen-fixing activities could not be detected in nitrogen-free culture media. The three strains shared 99.6–99.7 % 16S rRNA gene sequence similarity and showed 89–100 % DNA–DNA relatedness, suggesting that they represent a single genomic species. Phylogenetic analysis based on 16S rRNA gene sequences showed that strains d8-1^T, d8-2 and IMCC1716 formed a monophyletic branch in the periphery of the evolutionary radiation occupied by the genus Azonexus. Their closest neighbours were Azonexus caeni Slu-05^T (96.7–96.8 % similarity) and Azonexus fungiphilus BS5-8^T (96.3–96.6 %). The DNA–DNA relatedness of the novel strains to these two species of the genus Azonexus was less than 70 %. The isolates could also be differentiated from recognized members of the genus Azonexus on the basis of phenotypic and biochemical characteristics. It is evident, therefore, that the three strains represent a novel species of the genus Azonexus, for which the name Azonexus hydrophilus sp. nov. is proposed. The type strain is d8-1^T (=LMG 24005^T=BCRC 17657^T).

An electron micrograph of strain d8-1^T (Fig. S1) and a nifH gene sequence-based phylogenetic tree comprising the novel strains and related species (Fig. S2) are available with the online version of this paper.

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