Abstract: Analyzing the codon usage bias of the Exiguobacterium profundum NOS gene provides a theoretical basis for subsequent functional verification and genetic transformation studies. Research indicates that the codon usage bias of the E. profundum NOS gene is relatively weak, with a preference for G/C-ending codons. Comparative analysis of codon usage parameters among different bacterial NOS genes reveals variations in codon preferences, showing that actinobacteria NOS genes exhibit stronger codon bias than those of cyanobacteria and bacteria. Cluster analysis of CDS sequences and RSCU values of various bacterial NOS genes indicates that E. profundum NOS gene shares similar codon usage preferences with actinobacteria NOS genes. Neutral plot, PR2-plot, and ENc-plot analyses all suggest that natural selection is the primary factor influencing the codon usage bias of the NOS gene. Comparing the codon usage frequency with the genomes of seven model organisms, it is found that the E. coli prokaryotic expression system is more suitable for heterologous expression of E. profundum NOS than the yeast eukaryotic expression system. Among five common crops, rice is the most ideal host for genetic transformation of the E. profundum NOS gene. This study preliminarily reveals the codon usage pattern of the E. profundum NOS gene, providing important guidance for subsequent gene function validation and offering scientific insights into the molecular evolution of nitric oxide.

Key words: Exiguobacterium profundum, NOS gene, codon, usage bias