昆虫共生菌沃尔巴克氏体(Wolbachia)的wsp基因密码子使用模式分析

沃尔巴克氏体(Wolbachia)主要感染昆虫等节肢动物,是一类革兰阴性共生细菌。为探讨昆虫纲共生菌Wolbachia的系统发育,研究Wolbachia基因组中进化速度较快的外膜蛋白基因wsp的密码子使用模式及影响因素,统计分析该基因的GC含量(GCall、GC1、GC2、GC3、GC3s)、有效密码子数(ENc)、相对同义密码子使用度(RSCU)等指标。结果显示:昆虫纲共生菌Wolbachia的wsp基因密码子偏好性均不强,昆虫纲不同目间共生菌Wolbachia的wsp基因碱基组成及ENc值差异较小;多数基因数据点沿标准曲线或在其附近分布,突变对碱基组成的影响较弱;18种由多个密码子编码的氨基酸中有11种氨基酸的偏好性密码子在昆虫纲7个目及对照蛛形纲1个目间均相同,有2种氨基酸的偏好性密码子在7个目间相同,这些密码子均以A/U结尾;供分析的140个wsp基因中仅编码6个半胱氨酸(Cys);对应分析中第1、第2向量轴贡献率均不高,分别为13.53%和12.49%,均与碱基组成(GC1、GC2、GC3)显著相关。综合各项分析认为,Wolbachia的wsp基因密码子偏好性不具有宿主分类特异性,密码子使用模式主要受碱基组成影响,而碱基组成主要受选择影响。

Analysis of Codon Usage Pattern of wsp Gene in Insect Symbiont Wolbachia

Wolbachia is an symbiotic Gram-negative bacterium that mainly infects insect and other arthropods.Wolbachia surface protein gene(wsp) has a faster evolutional speed in Wolbachia genome.To explore phylogeny of the insect-symbiotic bacterium Wolbachia,codon usage pattern of Wolbachia wsp gene and its influencing factors,GC contents(GCall,GC1,GC2,GC3,and GC3s),effective number of codons(ENc),and relative synonymous codon usage(RSCU) of this gene were calculated and analyzed.The results indicated that a generally weak codon bias was found in Wolbachia wsp genes.Little differences were found in base composition and ENc value among insect species from different orders of Insecta harboring Wolbachia.ENc values of most genes were distributed along or near the standard curve,suggesting that mutation has weak influence on base composition.Among the 18 amino acids encoded by multiple codons,11 preferred codons were shared by 7 orders of Insecta and the control order of Arachnoidea,and 2 preferred codons were shared by 7 orders,all of which ended with an A or U.Only 6 cysteine(Cys) amino acids were encoded in the 140 examined wsp genes.Contributions of the first axis and the second axis were not enough in the correspondence analysis,accounting for 13.53% and 12.49% respectively,being significantly correlated with the base composition(GC1,GC2 and GC3).The above analyses suggest that the codon bias of Wolbachia wsp gene has no host specificity.The codon usage pattern was mainly determined by base composition,which was in turn mainly determined by selection.