Flavobacterium psychrophilum is currently one of the main bacterial pathogens hampering the productivity of salmonid farming worldwide, and its control mainly relies on antibiotic treatments. To better understand the population structure of this bacterium and its mode of evolution, we have examined the nucleotide polymorphisms at 11 protein-coding loci of the core genome in a set of 50 isolates. These isolates were selected to represent the broadest possible diversity, originating from 10 different host fish species and four continents. The nucleotide diversity between pairs of sequences amounted to fewer than four differences per kilobase on average, corresponding to a particularly low level of diversity, possibly indicative of a small effective-population size. The recombination rate, however, seemed remarkably high, and as a consequence, most of the isolates harbored unique combinations of alleles (33 distinct sequence types were resolved). The analysis also showed the existence of several clonal complexes with worldwide geographic distribution but marked association with particular fish species. Such an association could reflect preferential routes of transmission and/or adaptive niche specialization. The analysis provided no clues that the initial range of the bacterium was originally limited to North America. Instead, the historical record of the expansion of the pathogen may reflect the spread of a few clonal complexes. As a resource for future epidemiological surveys, a multilocus sequence typing website based on seven highly informative loci is available.
@article{nicolas_population_2008,
Author = {Nicolas, Pierre and Mondot, Stanislas and Achaz,
Guillaume and Bouchenot, Catherine and Bernardet,
Jean-François and Duchaud, Eric},
Title = {Population structure of the fish-pathogenic bacterium
{Flavobacterium} psychrophilum},
Journal = {Applied and Environmental Microbiology},
Volume = {74},
Number = {12},
Pages = {3702--3709},
abstract = {Flavobacterium psychrophilum is currently one of the
main bacterial pathogens hampering the productivity of
salmonid farming worldwide, and its control mainly
relies on antibiotic treatments. To better understand
the population structure of this bacterium and its mode
of evolution, we have examined the nucleotide
polymorphisms at 11 protein-coding loci of the core
genome in a set of 50 isolates. These isolates were
selected to represent the broadest possible diversity,
originating from 10 different host fish species and
four continents. The nucleotide diversity between pairs
of sequences amounted to fewer than four differences
per kilobase on average, corresponding to a
particularly low level of diversity, possibly
indicative of a small effective-population size. The
recombination rate, however, seemed remarkably high,
and as a consequence, most of the isolates harbored
unique combinations of alleles (33 distinct sequence
types were resolved). The analysis also showed the
existence of several clonal complexes with worldwide
geographic distribution but marked association with
particular fish species. Such an association could
reflect preferential routes of transmission and/or
adaptive niche specialization. The analysis provided no
clues that the initial range of the bacterium was
originally limited to North America. Instead, the
historical record of the expansion of the pathogen may
reflect the spread of a few clonal complexes. As a
resource for future epidemiological surveys, a
multilocus sequence typing website based on seven
highly informative loci is available.},
doi = {10.1128/AEM.00244-08},
issn = {1098-5336},
language = {eng},
month = jun,
pmcid = {PMC2446562},
pmid = {18424537},
year = 2008
}
