Sphingomonas and Phenylobacterium As Major Microbiota in Thymic Epithelial Tumors

Abstract Background Microbiota has been reported to be closely associated with carcinogenesis and cancer progression. However, its involvement in the pathology of thymoma remains unknown. In this study, we aimed to identify thymoma-specific microbiota using resected thymoma samples. Methods Nineteen thymoma tissue samples were analyzed through polymerase-chain-reaction amplification and 16S rRNA gene sequencing. The subjects were grouped according to histology, driver mutation status in the GTF2I gene, PD-L1 status, and smoking habits. To identify the taxa composition of each sample, operational taxonomic units (OTUs) were classified on the effective tags with 97% identity. The Shannon index of the 97% identity OTUs was calculated to evaluate alpha diversity. The linear discriminant analysis effect size (LEfSe) method was used to compare the relative abundances of all bacterial taxa. Results We identified 107 OTUs in the tumor tissues, which were classified into 26 genera. Sphingomonas and Phenylobacterium were identified as abundant genera in almost all samples. No significant difference was determined in the alpha diversity within these groups; however, type A thymoma exhibited higher bacterial diversity than type B thymoma. Through LEfSe analysis, we identified the following differentially abundant taxa: Bacilli, Firmicutes, and Lactobacillales in type A thymoma; Proteobacteria in type B thymoma; Gammaproteobacteria in tumors harboring the GTF2I mutation; and Alphaproteobacteria in tumors without the GTF2I mutation. Conclusions Sphingomonas and Phenylobacterium were identified as dominant genera in thymic epithelial tumors. These genera appear to comprise thymoma-specific microbiota involved in tumor progression; thus, they could serve as targets for the prevention of thymoma.