Aerobiosis Increases the Genomic Guanine Plus Cytosine Content (GC%) in Prokaryotes

Abstract

The huge variation in the genomic guanine plus cytosine content (GC%) among prokaryotes has been explained by two mutually exclusive hypotheses, namely, selectionist and neutralist. The former proposals have in common the assumption that this feature is a form of adaptation to some ecological or physiological condition. On the other hand, the neutralist interpretation states that the variations are due only to different mutational biases. Since all of the traits that have been proposed by the selectionists either appeared to be limited to certain genera or were invalidated by the availability of more data, they cannot be considered as a selective force influencing the genomic GC% across all prokaryotes. In this report we show that aerobic prokaryotes display a significant increment in genomic GC% in relation to anaerobic ones. This is the first time that a link between a metabolic character and GC% has been found, independently of phylogenetic relationships and with a statistically significant amount of data.

Codon usage between genomes is constrained by genome-wide mutational processes

“…37; although see ref. 38), correlates closely with u 1 g ; thus, u 1 g is likely also specified by directional mutation pressure. In this article, we show that u 2 g is also determined by mutational pressures acting throughout the genome.…”

Correlations between genomic GC levels and optimal growth temperatures in prokaryotes

“…The neutralist explanation was weakened by three observations: (i) that higher GC levels were found in bacteria exposed to UV light, this increase reducing the presence of TpT dinucleotides that could form dimers causing DNA replication problems [8]; (ii) that in some cases high GC levels of prokaryotes were associated with high growth temperatures [9][10][11] and with aerobiosis [12]; and (iii) that the compositional shifts associated with mutator mutations [5] were within the error limits of the ultracentrifugation approach used to detect them and only concerned ''hot spots'' [13]. Finally, when a pair of completely sequenced closely related bacteria (Corynebacterium efficiens and C. glutamicum) were compared, the positive relationship between T opt and GC level was striking [14].…”

A selective force favoring increased G+C content in bacterial genes

“…This view was bolstered by sequence information showing that the base compositional differences among bacteria were most pronounced at synonymous and noncoding positions, sites that are thought to be under the least selective constraints (5). Furthermore, repeated attempts to link genomic base composition with an environmental factor or other selective processes have met with limited success (6)(7)(8)(9)(10).…”