Taxonomy of environmental strains related to Acinetobacter brisouii, with the proposal of Acinetobacter brisouisimilis sp. nov. and Acinetobacter brisouioides sp. nov., and an emended description of Acinetobacter brisouii.

This study clarifies the taxonomic status of environmental Acinetobacter strains related to Acinetobacter brisouii, originally described based on a single strain in 2010. We analysed 15 strains, comprising A. brisouii (n=3) originating from Southeast Asia and 2 provisional taxa, Taxon 25A (n=6) and Taxon 25B (n=6), isolated from wetland habitats in Czechia. Their genome sizes ranged from 2.9 to 3.3 Mb, with G+C contents of 41.2-41.8 mol%. Core-genome phylogeny placed these strains into a distinct, deep-branching clade within the genus, structured into three strongly supported subclades corresponding to A. brisouii, Taxon 25A and Taxon 25B. Genomic average nucleotide identity and digital DNA-DNA relatedness values were 95.9-99.7% and 66.1-98.3%, respectively, within the subclades/taxa, 91.6-93.9% and 44.9-54.6% between the subclades/taxa and <77% and <24% when the clade members were compared with other Acinetobacter species. The clade was further distinguished by metabolic and physiological traits and by whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry profiles. All strains showed minimum inhibitory concentrations of colistin of 4-16 mg l⁻¹, consistent with intrinsic resistance to polymyxins. Despite overall phenotypic similarity, the three taxa differed in several characteristics, including maximum growth temperature. We propose Acinetobacter brisouisimilis sp. nov. (type strain ANC 3789ᵀ=CCM 9537ᵀ=CCUG 78401ᵀ) and Acinetobacter brisouioides sp. nov. (type strain ANC 5584ᵀ=CCM 9536ᵀ=CCUG 78402ᵀ) for Taxon 25A and Taxon 25B, respectively, and provide an emended description of A. brisouii.