Salmonella Strains Isolated from Galápagos Iguanas Show Spatial Structuring of Serovar and Genomic Diversity

It is thought that dispersal limitation primarily structures host-associated bacterial populations because host distributions inherently limit transmission opportunities. However, enteric bacteria may disperse great distances during food-borne outbreaks. It is unclear if such rapid long-distance dispersal events happen regularly in natural systems or if these events represent an anthropogenic exception. We characterized Salmonella enterica isolates from the feces of free-living Galápagos land and marine iguanas from five sites on four islands using serotyping and genomic fingerprinting. Each site hosted unique and nearly exclusive serovar assemblages. Genomic fingerprint analysis offered a more complex model of S. enterica biogeography, with evidence of both unique strain pools and of spatial population structuring along a geographic gradient. These findings suggest that even relatively generalist enteric bacteria may be strongly dispersal limited in a natural system with strong barriers, such as oceanic divides. Yet, these differing results seen on two typing methods also suggests that genomic variation is less dispersal limited, allowing for different ecological processes to shape biogeographical patterns of the core and flexible portions of this bacterial species' genome

Sampling locations where fecal specimens were collected.

<p>Samples were collected from marine iguanas (<i>Amblyrhynchus cristatus</i>) on Isla San Cristóbal sites Punta Carola, La Lobería, Isla Santa Fe, Isla Plaza Sur and Isla Fernandina and from two species of land iguanas on three islands (<i>Conolophus pallidus</i> on Isla Santa Fe and <i>Conolophus subcristatus</i> on Isla Plaza Sur and Isla Fernandina). Black stars indicate the three major port towns of the Galápagos Islands, Puerto Baquerizo Moreno on Isla San Cristóbal, Puerta Ayora on Isla Santa Cruz, and Puerto Villamil on Isla Isabela.</p

Sampling site distributions of <i>Salmonella enterica</i> serovars isolated from Galápagos land and marine iguanas in 2005 and 2009.

*<p>Serogroups as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037302#pone.0037302-Grimont1" target="_blank">[52]</a>.</p>**<p>C = Punta Carola, Isla San Cristóbal, L = La Loberia, Isla San Cristóbal, P = Isla Plaza Sur, S = Isla Santa Fe, F = Isla Fernandina.</p>$<p>untyped isolate established as presumptive <i>Salmonella</i> spp. by metabolic assay but submission to the National Veterinary Services Laboratory was found to be contaminated and was not typed further.</p>&<p><i>S. enterica</i> isolates from 2005 were part of a previous study and are described further in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037302#pone.0037302-Wheeler1" target="_blank">[29]</a>.</p