Abstract
BackgroundHorizontal gene transfer (HGT) plays a major role in speciation and evolution of bacteria and archaea by controlling gene distribution within an environment. However, information that links HGT to a natural community using relevant population-genetics parameters and spatial considerations is scarce. The Great Salt Lake (Utah, USA) provides an excellent model for studying HGT in the context of biogeography because it is a contiguous system with dispersal limitations due to a strong selective salinity gradient. We hypothesize that in spite of the barrier to phylogenetic dispersal, functional characteristics—in the form of HGT—expand beyond phylogenetic limitations due to selective pressure.Methodology and ResultsTo assay the functional genes and microorganisms throughout the GSL, we used a 16S rRNA oligonucleotide microarray (Phylochip) and a functional gene array (GeoChip) to measure biogeographic patterns of nine microbial communities. We found a significant difference in biogeography based on microarray analyses when comparing Sørensen similarity values for presence/absence of function and phylogeny (Student's t-test; p = 0.005).Conclusion and SignificanceBiogeographic patterns exhibit behavior associated with horizontal gene transfer in that informational genes (16S rRNA) have a lower similarity than functional genes, and functional similarity is positively correlated with lake-wide selective pressure. Specifically, high concentrations of chromium throughout GSL correspond to an average similarity of chromium resistance genes that is 22% higher than taxonomic similarity. This suggests active HGT may be measured at the population level in microbial communities and these biogeographic patterns may serve as a model to study bacteria adaptation and speciation.
Highlights
Change in community composition with distance, time, and along environmental gradients (b-diversity) provides information about the mechanisms that generate and regulate microbial biodiversity [1,2,3,4,5,6,7] and provide insight into evolutionary history [8] and ecosystem function [9]
Evolution [10] and functional diversity [11] are all influenced by horizontal gene transfer (HGT), Horizontal gene transfer (HGT) is rarely linked to relevant population-genetics parameters and temporospatial considerations [12]
HGT is an important factor in the evolution of prokaryotes in promoting adaptation to novel environments by allowing the exchange of large amounts of genetic information that increases the fitness of a specific population within an ecological niche [47,48] and plays a large role in controlling gene distribution within an environment by controlling the growth of specific populations [22]
Summary
Change in community composition with distance, time, and along environmental gradients (b-diversity) provides information about the mechanisms that generate and regulate microbial biodiversity [1,2,3,4,5,6,7] and provide insight into evolutionary history [8] and ecosystem function [9]. Spatial distribution models have been applied successfully in microbial ecology [3,4,5,9,15,24], in some cases shifting the focus of biogeography from the taxonomic level to functional characteristics that enable survival [4,9]. This shift provides a foundation for detailed molecular-level analyses within the context of a sound ecological and evolutionary framework that is required for spatially determining the rate and extent of real world physical gene transfer [25,26]. We hypothesize that in spite of the barrier to phylogenetic dispersal, functional characteristics—in the form of HGT—expand beyond phylogenetic limitations due to selective pressure
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