About this Research Topic
The guanine-cytosine (GC) content of bacterial genomes is ranges between 13.5% (Candidatus Zinderia insecticola) and 74.9% (Anaeromyxobacter dehalogenans). The distribution is rather distinct from a normal (Gaussian) distribution. Genome size and GC content are weakly correlated in bacteria and archaea. The obligate host-associated bacteria (with the exception of Candidatus Hodgkinia cicadicola) have short and low GC content genomes. In bacterial genomes, mutations from GC to adenosine-thymine (AT) are more common than mutations from AT to GC. However, some bacteria, for example Actinobacteria, have maintained a high GC content genome. In addition, genomes with similar GC contents have similar oligonucleotide frequencies (genome signatures). The variations in bacterial and archaeal genome DNA sequences are not only explained by neutral mutations. The restriction-modification system, a virus resistance system, has induced palindromic DNA sequence avoidance in the genomes. On the other hand, bacteria have clustered, regularly interspaced, short palindromic repeats (CRISPRs), which function as another virus resistance system. Some nucleoid-associated proteins bind DNA regions with low GC content rather than the remaining chromosomal DNA and inhibit expression of the genes contained in those regions. This gene repression is also one of virus resistance systems. In addition, the virus resistance systems have influenced plasmid distribution. The plasmid DNA has lower GC content than its host chromosome DNA does. Most of the differences in GC content between plasmids and their host chromosomes are of less than 10%, suggesting that host organisms cannot maintain and regulate plasmids with very different GC content from their own. Therefore, virus resistance systems have resulted in changes in bacterial and archaeal genome DNA sequences during evolution. Where did plasmids and viruses come from? I hypothesize that origin of plasmids and viruses is a part of genome DNA (See image). Mobile genetic elements may have played a role in the plasmid and virus genesis, which is related to genome reduction. Although plasmids and viruses are allies and foes of cells respectively, plasmids and viruses have co-evolved with cells. I am interested in the relation between bacterial (or archaeal) genome sequence and their functions. I welcome investigators to contribute any types of the tier 1 articles focusing on the evolution and function of bacterial (or archaeal) genome sequences to this Research Topic.
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