Environmental Origin of the GenusBordetella.
Members of the genusBordetellainclude human and animal pathogens that cause a variety of respiratory infections, including whooping cough in humans. Despite the long known ability to switch between a within-animal and an extra-host lifestyle under laboratory growth conditions, no extra-host niches of pathogenicBordetellaspecies have been defined. To better understand the distribution ofBordetellaspecies in the environment, we probed the NCBI nucleotide database with the 16S ribosomal RNA (16S rRNA) gene sequences from pathogenicBordetellaspecies. Bacteria of the genusBordetellawere frequently found in soil, water, sediment, and plants. Phylogenetic analyses of their 16S rRNA gene sequences showed thatBordetellarecovered from environmental samples are evolutionarily ancestral to animal-associated species. Sequences from environmental samples had a significantly higher genetic diversity, were located closer to the root of the phylogenetic tree and were present in all 10 identified sequence clades, while only four sequence clades possessed animal-associated species. The pathogenic bordetellae appear to have evolved from ancestors in soil and/or water. We show that, despite being animal-adapted pathogens,Bordetella bronchiseptica, andBordetella hinziihave preserved the ability to grow and proliferate in soil. Our data implicate soil as a probable environmental origin ofBordetellaspecies, including the animal-pathogenic lineages. Soil may further constitute an environmental niche, allowing for persistence and dissemination of the bacterial pathogens. Spread of pathogenic bordetellae from an environmental reservoir such as soil may potentially explain their wide distribution as well as frequent disease outbreaks that start without an obvious infectious source.
Department of Infectious Diseases, University of GeorgiaAthens, GA, USA; Center for Vaccines and Immunology, University of GeorgiaAthens, GA, USA.
Illiassou
I
Hamidou Soumana
Center for Vaccines and Immunology, University of GeorgiaAthens, GA, USA; Department of Veterinary and Biomedical Sciences, Pennsylvania State UniversityUniversity Park, PA, USA.
Bodo
B
Linz
Department of Infectious Diseases, University of GeorgiaAthens, GA, USA; Center for Vaccines and Immunology, University of GeorgiaAthens, GA, USA; Department of Veterinary and Biomedical Sciences, Pennsylvania State UniversityUniversity Park, PA, USA.
Eric T
ET
Harvill
Bordetella; ecological niches; environmental origin; environmental strains; extra-host adaptation