Functional biogeography as evidence of gene transfer in hypersaline microbial communities.
BACKGROUND
Horizontal 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.


RESULTS
To 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).


CONCLUSIONS
Biogeographic 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.
Center for Integrated BioSystems, Utah State University, Logan, Utah, United States of America. jacob.parnell@usu.edu
J Jacob
JJ
Parnell
Giovanni
G
Rompato
Leigh C
LC
Latta
Michael E
ME
Pfrender
Joy D
JD
Van Nostrand
Zhili
Z
He
Jizhong
J
Zhou
Gary
G
Andersen
Patti
P
Champine
Balasubramanian
B
Ganesan
Bart C
BC
Weimer
D001419:Bacteria / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012965:Sodium Chloride / Q000378:metabolism*; D014589:Utah; D014871:Water Microbiology
D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012965:Sodium Chloride