Summary auto-generated
This study characterizes five Actinomyces-like bacterial strains isolated from human clinical specimens, including blood and urine cultures. Using biochemical tests, cellular fatty acid analysis, whole-cell protein profiling, and 16S rRNA gene sequencing, researchers determined these isolates represent a previously unknown species. The organisms are gram-positive, facultatively anaerobic, catalase-negative rods that ferment limited sugars and produce acetate as a major metabolic end product. Phylogenetic analysis revealed approximately 94% 16S rRNA sequence similarity to Actinomyces suis, but greater than 6% sequence divergence demonstrated they constitute a distinct species. Based on these findings and prior taxonomic studies showing Actinomyces suis warrants separate classification, the authors propose establishing a new genus, Actinobaculum. They reclassify A. suis as Actinobaculum suis comb. nov. and describe the novel human-derived isolates as Actinobaculum schaalii sp. nov., with strain CCUG 27420 designated as the type strain. The new genus forms a distinct phylogenetic lineage within gram-positive bacteria with Arcanobacterium as its closest relative.
Key findings
- Five previously uncharacterized Actinomyces-like isolates from human blood and urine were identified as a new bacterial species based on biochemical, protein, and genetic analysis
- The new isolates show approximately 94% 16S rRNA similarity to Actinomyces suis but >6% sequence divergence, confirming they represent a distinct species
- A new bacterial genus Actinobaculum is proposed to accommodate Actinomyces suis and the novel human-derived species due to phylogenetic distinctiveness from the heterogeneous Actinomyces genus
- Actinobaculum schaalii sp. nov. is distinguished from A. suis by acid production from glucose and D-xylose, lack of glycogen fermentation, and absence of β-glucuronidase and urease activities
- The new genus Actinobaculum forms a distinct phylogenetic lineage with Arcanobacterium as its closest relative among gram-positive bacteria
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
Five strains of a hitherto unknown Actinomyces-like bacterium were isolated from human clinical sources, including blood cultures. Biochemical and chemotaxonomic characterization indicated that the strains were distinct from previously described Actinomyces and Arcanobacterium species. A comparative 16S rRNA gene sequence analysis demonstrated that the undescribed strains constitute a new subline within the Actinomyces-Arcanobacterium species complex. The closest known relative of the isolates was found to be Actinomyces suis, although a 16S rRNA sequence divergence value of approximately 6% clearly demonstrated that the unknown bacterium represents a distinct species. Based on the results of the present and earlier phylogenetic investigations, it is proposed that Actinomyces suis should be reclassified in a new genus, the genus Actinobaculum, as Actinobaculum suis comb. nov. In addition, a new species, Actinobaculum schaalii, is proposed for the Actinomyces-like bacterium from human sources. The type strain of Actinobaculum schaalii is CCUG 27420.