Bacterial strain G20-18T was previously isolated from the rhizosphere of an Arctic grass on Ellesmere Island, Canada and was characterized and described as Pseudomonas fluorescens. However, new polyphasic analyses coupled with phenotypic, phylogenetic and genomic analyses reported here demonstrate that the affiliation to the species P. fluorescens was incorrect. The strain is Gram-stain-negative, rod-shaped, aerobic and displays growth at 5-25 °C (optimum, 20-25 °C), at pH 5-9 (optimum, pH 6-7) and with 0-4 % NaCl (optimum, 2 % NaCl). The major fatty acids are C16 : 0 (35.6 %), C17 : 0 cyclo ω7c (26.3 %) and summed feature C18 : 1/C18 : 1 ω7c (13.6 %). The respiratory quinones were determined to be Q9 (93.5 %) and Q8 (6.5 %) and the major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. Strain G20-18T was shown to synthesize cytokinin and auxin plant hormones and to produce 1-aminocyclopropane-1-carboxylate deaminase. The DNA G+C content was determined to be 59.1 mol%. Phylogenetic analysis based on the 16S rRNA gene and multilocus sequence analysis (concatenated 16S rRNA, gyrB, rpoB and rpoD sequences) showed that G20-18T was affiliated with the Pseudomonas mandelii subgroup within the genus Pseudomonas. Comparisons of the G20-18T genome sequence and related Pseudomonas type strain sequences showed an average nucleotide identity value of ≤93.6 % and a digital DNA-DNA hybridization value of less than 54.4 % relatedness. The phenotypic, phylogenetic and genomic data support the hypothesis that strain G20-18T represents a novel species of the genus Pseudomonas. As strain G20-18T produces or modifies hormones, the name Pseudomonas hormoni sp. nov. is proposed. The type strain is G20-18T (=LMG 33086T=NCIMB 15469T).
Keywords: ACC deaminase; IAA; Pseudomonas mandelii subgroup; auxin; cytokinin; phylogenomics; plant hormones.