title: Positive correlations between genomic %AT and genome size within strains of bacterial species.
abstract: Genomic %AT has been found to correlate negatively with genome size in microbes. While microbes with large genomes are often GC rich and free living, AT-rich bacteria tend to be host associated with smaller genomes. With over 2000 fully sequenced and assembled microbial genomes available, we explored the relationship among genomic %AT, genome size, relative entropy (a measure associated with genetic drift) and fraction of genome islands (GIs) in microbial species with the genomes of more than 10 strains available. A negative correlation with genome size was found in six out of 12 phylogenetic groups and subphyla and a positive correlation in only two. At the species level, we found a trend of positive correlations between genomic %AT and genome size in eight out of 20 species, while only four showed a negative correlation. Estimated chromosomal fractions of GIs were found to correlate positively with genome size in the strains of 14 out of 18 species and genomic %AT in the strains of seven species (two correlated negatively). Although GIs explain most of the observed positive correlations between genomic %AT and size, Chlamydia trachomatis seem to be an exception; therefore, these findings needs to be further explored.
authors.affiliation: Division of Epidemiology, Norwegian Institute of Public Health, Marcus Thranes Gate 6, P.O. Box 4404, 0403, Oslo, Norway; Epi-Centre, Department of Food-Safety and Infection Biology, Norwegian School of Veterinary Science, Ullevålsveien 72, P.O. Box 8146 Dep, NO-0033, Oslo, Norway.
authors.forename: Jon
authors.initials: J
authors.lastname: Bohlin
authors.forename: Camilla
authors.initials: C
authors.lastname: Sekse
authors.forename: Eystein
authors.initials: E
authors.lastname: Skjerve
authors.forename: Ola
authors.initials: O
authors.lastname: Brynildsrud
mesh_terms: D001419:Bacteria / Q000235:genetics*; D001482:Base Composition; D059646:Genome Size; D016680:Genome, Bacterial