Analysis of evolutionary patterns of genes in Campylobacter jejuni and C. coli
1 Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway
2 , Molecular Microbiology and Genomics Consultants, Zotzenheim, Germany
3 Ruminant Nutrition and Microbiology, AgResearch Limited, Grasslands Research Centre, Palmerston North, New Zealand
4 Department of Microbiology, North Carolina State University, Raleigh, North Carolina, USA
5 Department of Food, Bioprocessing & Nutrition Sciences, North Caroline State University, North Carolina, Raleigh, USA
6 Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, Dept. of Biology, P.O. Box 1066 Blindern 0316 Oslo, Norway and Centre for Molecular Biology and Neuroscience, Institute of Medical Microbiology, Oslo University Hospital, Oslo, Norway
7 Department of Food Science, Faculty of Life Sciences, Copenhagen University, Copenhagen, Denmark
8 Centre for Biological Sequence Analysis, Technical University of Denmark, Lyngby, Denmark
9 Bacterial Epidemiology and Antimicrobial Resistance Research Unit, Richard B. Russell Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, Athens, Georgia, USA
10 , Riddet Institute, hosted by Massey University, Palmerston North, Private Bag 11222, New Zealand
Microbial Informatics and Experimentation 2012, 2:8 doi:10.1186/2042-5783-2-8Published: 28 August 2012
The thermophilic Campylobacter jejuni and Campylobacter coli are considered weakly clonal populations where incongruences between genetic markers are assumed to be due to random horizontal transfer of genomic DNA. In order to investigate the population genetics structure we extracted a set of 1180 core gene families (CGF) from 27 sequenced genomes of C. jejuni and C. coli. We adopted a principal component analysis (PCA) on the normalized evolutionary distances in order to reveal any patterns in the evolutionary signals contained within the various CGFs.
The analysis indicates that the conserved genes in Campylobacter show at least two, possibly five, distinct patterns of evolutionary signals, seen as clusters in the score-space of our PCA. The dominant underlying factor separating the core genes is the ability to distinguish C. jejuni from C. coli. The genes in the clusters outside the main gene group have a strong tendency of being chromosomal neighbors, which is natural if they share a common evolutionary history. Also, the most distinct cluster outside the main group is enriched with genes under positive selection and displays larger than average recombination rates.
The Campylobacter genomes investigated here show that subsets of conserved genes differ from each other in a more systematic way than expected by random horizontal transfer, and is consistent with differences in selection pressure acting on different genes. These findings are indications of a population of bacteria characterized by genomes with a mixture of evolutionary patterns.