DNA-rRNA Hybridization Studies among Brochothrix spp. and Some Other Gram-Positive Bacteria

This study used DNA-rRNA hybridization to confirm that Brochothrix campestris, a recently described species, belongs to the genus Brochothrix. The researchers extracted and labeled rRNA from B. campestris and measured its hybridization to DNA from various gram-positive bacteria to determine genetic relationships. Results showed that B. campestris is genuinely related to B. thermosphacta at the genus level (ΔTm value of 1°C). B. campestris is most closely related to Listeria species (Listeria innocua and L. monocytogenes), with ΔTm values of 4.5-5.0°C, indicating these genera share many characteristics including catalase and cytochromes. The bacterium also showed relatedness to Enterococcus faecalis and Bacillus cereus/subtilis. However, B. campestris showed no specific relationship to Arthrobacter globiformis, the genus to which B. thermosphacta was originally assigned. The findings support reclassification of B. campestris within Brochothrix rather than Microbacterium.

Key findings

• B. campestris definitively belongs in the genus Brochothrix based on DNA-rRNA hybridization analysis
• B. campestris is most closely related to Listeria species and also related to Enterococcus and Bacillus genera
• B. campestris shares biochemical characteristics with Listeria including catalase production and methyl-branched fatty acids
• The two Brochothrix species show low DNA-DNA homology (13-17%) but genuine genus-level relationship by rRNA analysis
• B. campestris is distantly related to lactic acid bacteria and shows no relationship to Arthrobacter globiformis