Soil collected in the Great Smoky Mountains National Park yielded a novel Listeria species, L. swaminathanii, effectively expanding the sensu stricto clade to ten species

Soil samples collected in the Great Smoky Mountains National Park yielded a Listeria isolate that could not be classified to the species level. Whole-genome sequence-based average nucleotide identity BLAST and in silico DNA-DNA Hybridization analyses confirmed this isolate to be a novel Listeria sensu stricto species with the highest similarity to L. marthii (ANI=93.9%, isDDH=55.9%). Additional whole-genome-based analysis using the Genome Taxonomy Database Toolkit, an automated program for classifying bacterial genomes, further supported delineation as a novel Listeria sensu stricto species, as this tool failed to assign a species identification but identified L. marthii as the closest match. Phenotypic and genotypic characterization results indicate that this species is nonpathogenic. Specifically, the novel Listeria species described here is phenotypically (i) non-hemolytic and (ii) negative for phosphatidylinositol-specific phospholipase C activity; the draft genome lacks all virulence genes found in the Listeria pathogenicity island 1 (LIPI-1), as well as the internalin genes inlA and inlB. While the type strain for the new species is phenotypically catalase-negative (an unusual characteristic for Listeria sensu stricto species), its genome contained an apparently intact catalase gene (kat); hence assessment of this phenotype with future isolates will be important. Rapid species identification systems (Listeria API, VITEK 2, VITEK MS) misidentified this novel species as either L. monocytogenes, L. innocua, or L. marthii. We propose the name L. swaminathanii, and the type strain is FSL L7-0020T (=ATCC TSD-239T).