Azospirillum caeni sp. nov., a mesotrione-resistant and nitrogen-fixing bacterium isolated from an activated sludge.

Authors

Minglai Wan, Chenghui Li, Le Chen, Xiaodong Hou, Jian He, Baolong Zhang

Published in

International journal of systematic and evolutionary microbiology. Volume 76. Issue 7.

Abstract

A Gram-stain-negative, facultative anaerobic, short rod-shaped, non-spore-forming, mesotrione-resistant bacterium, designated strain A39^T, was isolated from activated sludge treating pesticide-manufacturing wastewater. Strain A39^T grew at 15-42 ℃, pH 6-10 and 0-1.0% NaCl (w/v), tolerated up to 2 mM mesotrione and could fix nitrogen. Strain A39^T showed the highest 16S rRNA gene sequence similarity to Azospirillum halopraeferens Au 4^T (98.1%) and less than 97% sequence similarity with other species of the genus Azospirillum. Phylogenetic analysis based on 16S rRNA gene and genome sequences placed strain A39^T within genus Azospirillum, forming a subclade with A. halopraeferens Au 4^T. The values of digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) between strain A39^T and A. halopraeferens Au 4^T were 25.5% and 82.7%, respectively, which were significantly below the recommended thresholds for species delineation (dDDH <70% and ANI <95-96%). The major fatty acids were summed feature 8 (C_18 : 1  ω7c/C1_8 : 1  ω6c), C_16 : 0 and C_18 : 0. Strain A39^T comprised phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, glycolipid and two aminolipids as the predominant polar lipids; and ubiquinone 10 as the major respiratory quinone. The genome size was 8.1 Mb with a DNA G+C content of 72.1%. Based on the phylogenetic, phenotypic and chemotaxonomic characteristics, strain A39^T represented a novel species of the genus Azospirillum, for which the name Azospirillum caeni sp. nov. is proposed. The type strain is A39^T (=MCCC 1K09771^T=KCTC 18385^T). Additionally, a gene encoding 4-hydroxyphenylpyruvate dioxygenase (HPPD), named AzhppD, was identified in strain A39^T. AzHPPD showed less than 61% similarity to previously reported HPPDs and was able to tolerate 30 µM of mesotrione, which is an inhibitor of HPPD.

PMID:
42446519
Bibliographic data and abstract were imported from PubMed on 14 Jul 2026.

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