Azospirillum Aestuarii sp. nov., a Novel Nitrogen-Fixting and Aerobic Denitrifying Bacteria Isolated from an Estuary of a Freshwater River.

A novel Gram-staining negative, aerobic, rod-shaped bacterium, designated strain YIM DDC1, was isolated from an estuary sediment sample of Dongda River flowing into Dianchi lake in Yunnan, southwest China. The strain displayed growth at 10-40 °C (optimum of 28 °C), pH 5.0-9.0 (optimum of 7.0-8.0) and in presence of 0-3% (w/v) NaCl (optimum of 0-1%). Strain YIM DDC1 comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and two unidentified aminolipids as the predominant polar lipids; the ubiquinone 10 as the major respiratory quinone; and summed feature 8 (Cω6c and/or Cω7c), summed feature 3 (Cω7c and/or Cω6c) and C 2-OH as the major cellular fatty acids. Analysis of 16S rRNA showed that YIM DDC1 represents a member of the genus Azospirillum, and was closely related to A. brasilense ATCC 29145 (98.9%), A. baldaniorum Sp245 (98.2%), A. argentinense Az39 (98.2%) and A. formosense CC-Nfb-7 (98.2%). The draft genome size was 7.15 Mbp with a 68.4% G + C content. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain YIM DDC1 and the aforementioned closely related strains exhibited similarity in the range of 93.8-93.5% and 53.7-52.7%, respectively. nif gene cluster (nifHDK) and denitrification genes ((napA, nirS, nirK, norBC and nosZ) detected in the genome indicated its potential nitrogen fixation and full-fledged denitrifying function. Based on combined genotypic and phenotypic data, strain YIM DDC1 represents a novel species of the genus Azospirillum, for which the name Azospirillum aestuarii sp. nov. is proposed. The type strain is YIM DDC1 (= KCTC 42887 = CGMCC 1.17325).