Characterization of Codon Usage Bias in the RA Ragb/SusD Gene

Abstract

The analysis on codon usage bias of Riemerella anatipestifer (RA) RagB/SusD gene (GenBank accession No. NC_017045.1) may improve our understanding of the evolution and pathogenesis of RA and provide a basis for understanding the relevant mechanism for biased usage of synonymous codons and for selecting appropriate expression systems to improve the expression of target genes. In this study, the synonymous codon usage in the RagB/SusD gene of RA and 19 reference bacteroidetes have been investigated. The results showed that codon usage bias in the RagB/SusD gene was strong bias towards the synonymous codons with A and T at the third codon position. A high level of diversity in codon usage bias existed, and the effective number of codons used in a gene plot revealed that the genetic heterogeneity in RagB/SusD gene of bacteroidetes was constrained by the G + C content. The codon adaptation index (CAI), effective number of codons (ENC), and GC3S values indicated synonymous codon usage bias in the RagB/SusD gene of bacteroidetes, and this synonymous bias was correlated with host evolution. The phylogentic analysis suggested that RagB/SusD was evolutionarily closer to Ornithobacterium rhinotracheale and that there was no significant deviation in codon usage in different bacteroidetes. There are 25 codons showing distinct usage differences between RA RagB/SusD and E. coli, 30 between RA RagB/SusD and Homo sapiens, 26 codons between RA RagB/SusD and yeast. Therefore the yeast and E. coli expression system may be suitable for the expression of RA RagB/SusD gene if some codons could be optimized.