Proposal of Acinetobacter thermotolerans sp. nov. to accommodate bovine feces-dwelling bacteria growing at 47 °C.

This study aimed to determine the taxonomic status of a new group of bovine strains of the genus Acinetobacter characterized by the rare ability to grow at temperatures above 44 °C. Initially, 24 strains were isolated from cattle feces collected at 11 farms in Czechia in 2022, representing a tentative new species based on preliminary whole-cell MALDI-TOF MS identification and rpoB gene sequencing. Twelve strains encompassing the within-group diversity were studied in detail, including whole genome de novo sequencing. Core genome-based phylogenetic analysis revealed that the 12 strains form a distinct clade within the genus. The genomic average nucleotide identity based on BLAST (ANIb) values within the clade were ≥ 98.2%, whereas the ANIb values between the clade and the known Acinetobacter species were < 83%. Each of the 12 genomes consisted of a circular chromosome (3.05-3.28 Mb) and 1-6 extrachromosomal elements (1.43-122.5 kb). All strains were non-glucose oxidizing, non-hemolytic, non-proteolytic, and prototrophic, and used acetate, ethanol, and DL-lactate as sole carbon and energy sources. Unrestricted growth at 47 °C was their unique diagnostic characteristic in a genus-wide comparative analysis and their growth kinetics at 37-46 °C differed from that of Acinetobacter baumannii. The studied strains were susceptible to 18 antibiotics except for sporadic resistance to streptomycin, tetracycline, and sulfonamides associated with the presence of strA/strB, tet(Y), and sul2 genes, respectively. We conclude that the studied strains represent a new species, for which we propose the name Acinetobacter thermotolerans sp. nov. The type strain is ANC 7454T (= CCM 9356T = CCUG 77195T = CNCTC 8200T).