Relative entropy differences in bacterial chromosomes, plasmids, phages and genomic islands.
BACKGROUND
We sought to assess whether the concept of relative entropy (information capacity), could aid our understanding of the process of horizontal gene transfer in microbes. We analyzed the differences in information capacity between prokaryotic chromosomes, genomic islands (GI), phages, and plasmids. Relative entropy was estimated using the Kullback-Leibler measure.


RESULTS
Relative entropy was highest in bacterial chromosomes and had the sequence chromosomes > GI > phage > plasmid. There was an association between relative entropy and AT content in chromosomes, phages, plasmids and GIs with the strongest association being in phages. Relative entropy was also found to be lower in the obligate intracellular Mycobacterium leprae than in the related M. tuberculosis when measured on a shared set of highly conserved genes.


CONCLUSIONS
We argue that relative entropy differences reflect how plasmids, phages and GIs interact with microbial host chromosomes and that all these biological entities are, or have been, subjected to different selective pressures. The rate at which amelioration of horizontally acquired DNA occurs within the chromosome is likely to account for the small differences between chromosomes and stably incorporated GIs compared to the transient or independent replicons such as phages and plasmids.
Norwegian School of Veterinary Science, EpiCentre, Department of Food Safety and Infection biology, Ullevålsveien 72, Oslo, Norway. jon.bohlin@nvh.no
Jon
J
Bohlin
Mark W J
MW
van Passel
Lars
L
Snipen
Anja B
AB
Kristoffersen
David
D
Ussery
Simon P
SP
Hardy
D001435:Bacteriophages / Q000235:genetics*; D002876:Chromosomes, Bacterial / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry; D019277:Entropy; D022761:Gene Transfer, Horizontal; D044404:Genomic Islands; D009166:Mycobacterium leprae / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000235:genetics; D010957:Plasmids / Q000235:genetics*
D004269:DNA, Bacterial