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The strain KG01 T was isolated from a soil sample from King George Island, Antarctica. Cells of KG01 T are rod-shaped and motile by means of multiple polar flagella. The absence of arginine dihydrolase activity could be a key feature to readily distinguish KG01 T from its closest phylogenetic relative species. The main fatty acids of the strain include summed feature 3 (C 16 : 1  ω7 c and/or C 15 : 0 iso 2-OH), C 16 : 0 and C 18 : 1  ω7 c . Phylogenetic analysis based on the 16S rRNA gene sequence and on a multilocus sequence analysis (MLSA) using housekeeping genes (16S rRNA , rpoB, rpoD, gyrB ) were carried out. These analyses allowed us to include the strain within the Pseudomonas fluorescens group, presenting the highest similarity of multilocus sequence with Pseudomonas veronii LMG 17761 T (96.67 %). The genome of KG01 T was sequenced and in silico compared with genomes of the most closely related species of the P. fluore scens group. The average nucleotide identity (ANIb) and average amino acid identity (AAI) values of the species phylogenetically closest to KG01 T were less than 95-96 %, threshold currently accepted to define strain as belonging to a bacterial species, the highest scores being those to Pseudomonas veronii LMG 17761 T (87.98 %) and Pseudomonas marginalis ICMP 3553 T (91.90 %). Therefore, the phenotypic and genotypic analyses results, allow us to propose that KG01 T represents a member of a novel species of the genus Pseudomonas , for which the name Pseudomonas fildesensis is proposed, and KG01 T (=CECT 9084 T ;=DSM 102036 T ) is established as the type strain .

Antarctica harbors a great diversity of microorganisms, including bacteria, archaea, microalgae and yeasts. The Pseudomonas genus is one of the most diverse and successful bacterial groups described to date, but only eight species isolated from Antarctica have been characterized. Here, we present three potentially novel species isolated on King George Island. The most abundant isolates from four different environments, were genotypically and phenotypically characterized. Multilocus sequence analysis and 16S rRNA gene analysis of a sequence concatenate for six genes (16S, aroE, glnS, gyrB, ileS and rpoD), determined one of the isolates to be a new Pseudomonas mandelii strain, while the other three are good candidates for new Pseudomonas species. Additionally, genotype analyses showed the three candidates to be part of a new subgroup within the Pseudomonas fluorescens complex, together with the Antarctic species Pseudomonas antarctica and Pseudomonas extremaustralis. We propose terming this new subgroup P. antarctica. Likewise, phenotypic analyses using API 20 NE and BIOLOG ® corroborated the genotyping results, confirming that all presented isolates form part of the P. fluorescens complex. Pseudomonas genus research on the Antarctic continent is in its infancy. To understand these microorganisms' role in this extreme environment, the characterization and description of new species is vital., (Copyright © 2018 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. All rights reserved.)