Comparative characterization analysis of synonymous codon usage bias in classical swine fever virus

Classical swine fever virus (CSFV) is responsible for the highly contagious viral disease of swine, and causes great economic loss in the swine-raising industry. Considering the significance of CSFV, a systemic analysis was performed to study its codon usage patterns. In this study, using the complete genome sequences of 76 CSFV representing three genotypes, we firstly analyzed the relative nucleotide composition, effective number of codon (ENC) and synonymous codon usage in CSFV genomes. The results showed that CSFV is GC-moderate genome and the third-ended codons are not preferentially used. Every ENC values in CSFV genomes are >50, indicating that the codon usage bias is comparatively slight. Subsequently, we performed the correspondence analysis (COA) to investigate synonymous codon usage variation among all of the CSFV genomes. We found that codon usage bias in these CSFV genomes is greatly influenced by G + C mutation, which suggests that mutational pressure may be the main factor determining the codon usage biases. Moreover, most of the codon usage bias among different CSFV ORFs is directly related to the nucleotide composition. Other factors, such as hydrophobicity and aromaticity, also influence the codon usage variation among CSFV genomes. Our study represents the most comprehensive analysis of codon usage patterns in CSFV genome and provides a basic understanding of the mechanisms for its codon usage bias.