Significance and roles of synonymous codon usage in the evolutionary process of Proteus

Study on the Characteristic Codon Usage Pattern in Porcine Epidemic Diarrhea Virus Genomes and Its Host Adaptation Phenotype

Porcine epidemic diarrhea virus (PEDV), which classified in the genus Alphacoronavirus, family Coronaviridae, is one of the most important pathogens that cause heavy economic losses in pig industry. Although intensive mutation and recombination analysis of PEDV strains were provided, systematic genome analysis were needed to elucidate the evolution mechanism and codon usage adaptation profiles of the pathogen. Here, a comprehensive investigation was carried out to reveal the systematic evolutionary processes of synonymous codon usage and host-adapted evolution phenotype of PEDV genome. We found a low codon usage bias (CUB) in PEDV genome and that nucleotide compositions, natural selection, mutation pressure and geographical diversity shapes the codon usage patterns of PEDV, with natural selection dominated the overall codon usage bias in PEDV than the others. By using the relative codon deoptimization index (RCDI) and similarity index (SiD) analysis, we observed that genotype II PEDV strains showed the highest level of adaptation phenotype to Sus scrofa than another divergent clade. To the best of our knowledge, this is the first comprehensive report elaborating the codon usage and host adaptation of PEDV. The findings offer an insight into our understanding of factors involved in PEDV evolution, adaptation and fitness toward their hosts.

The nucleotide usages significantly impact synonymous codon usage in Mycoplasma hyorhinis

Five annotated genomes of Mycoplasma hyorhinis were analyzed for clarifying evolutionary dynamics driving the overall codon usage pattern. Information entropy used for estimating nucleotide usage pattern at the gene level indicates that multiple evolutionary dynamics participate in forcing nucleotide usage bias at every codon position. Moreover, nucleotide usage bias directly contributes to synonymous codon usage biases with two different extremes. The overrepresented codons tended to have A/T in the third codon position, and the underrepresented codons strongly used G/C in the third position. Furthermore, correspondence analysis and neutrality plot reflect an obvious interplay between mutation pressure and natural selection mediating codon usage in M. hyorhinis genome. Due to significant bias in usages between A/T and G/C at the gene level, different selective forces have been proposed to contribute to codon usage preference in M. hyorhinis genome, including nucleotide composition constraint derived from mutation pressure, translational selection involved in natural selection, and strand-specific mutational bias represented by different nucleotide skew index. The systemic analyses of codon usage for M. hyorhinis can enable us to better understand the mechanisms of evolution in this species.

Tracing Brucella evolutionary dynamics in expanding host ranges through nucleotide, codon and amino acid usages in genomes

The host range of Brucella organisms has expanded from terrestrial and marine mammals to fish and amphibians. The high homology genomes of different Brucella organisms promote us to investigate evolutionary patterns for nucleotide, codon and amino acid usage patterns at gene levels among Brucella species. Although the similar patterns for nucleotide and synonymous codon usages exist in gene population, GC composition at the first codon position has significant correlations to that of the second and third codon positions, respectively, suggesting that nucleotide usages surrounding one codon influence synonymous codon usage patterns. Evolutionary patterns represented by synonymous codon and amino acid usages reflect host factor impacting Brucella speciation. As for genetic variations of important virulent factors involved with different biological functions, genes encoding lipoplysaccharides (LPSs) display more distinctive codon adaptation to Brucella than those of the BvrR/BvrS system and type IV secretion system. By Bayesian analysis, the polygenetic constructions for these genes of virulent factors shared by Brucella species display the purifying/positive selections and partially host factor in mediating genetic variations of these genes. The systemic analyses for nucleotide, synonymous codon and amino acid usages at gene level and genetic variations of important virulent factor genes display that host limitation influences either genetic characterizations at gene level or a particular gene involved in virulent factors of Brucella.Communicated by Ramaswamy H. Sarma.