Background Esophageal cancer is a common gastrointestinal tumor with a high incidence in China. Some studies suggest that intestinal flora is significantly related to the occurrence and development of tumors and other diseases. Traditional 16S rDNA sequencing technology only provides taxonomic resolution at genus level.

Objective Based on PacBio single molecule real time (SMRT) sequencing technology to identify characteristic microbial biomarkers associated with esophageal cancer at the species level.

Methods A total of 120 newly diagnosed cases of esophageal cancer were recruited and 60 healthy patients with matched sex and age were recruited as the control group. Fresh stool samples were collected from all subjects. Full-length 16S rDNA sequencing was performed on samples from 4 patients with esophageal cancer and 1:1 matched healthy controls using the third-generation sequencing PacBio SMRT technology, and the structural differences of intestinal flora were analyzed based on the sequencing results. Function prediction was performed by PICRUSt software. Large population samples were validated by screening different gut microbes by linear discriminant analysis and linear discriminant analysis effect size to identify esophageal cancer-associated gut microbes.

Results Based on sequencing samples, the results of α diversity analysis showed that the Ace, Chao1, Simpson Diversity, and Shannon Wiener indices of the esophageal cancer group were higher than those of the healthy control group (P<0.05), and the results of β diversity showed that the scattered clusters of the esophageal cancer group and the healthy control group were separated, which meant that there were differences in the structure of intestinal flora between the two groups. It was found at the phylum level that the abundances of Proteobacteria, Bacteroidetes, and Firmicutes in the intestinal flora of the esophageal cancer group were increased. At the genus level, the relative abundances of Spirospira, Pasteurella, Roxella, and Bacteroides in the esophageal cancer group were increased. At the species level, there were 11 microbial species with increased relative abundances in the esophageal cancer group, including Enterobacter sp. E.20, Bacteroides ovatus V975, and Faecalibacterium prausnitzii, and the microbial species with decreased relative abundances in the esophageal cancer group were Ralstonia pickettii, Enterobacter unclassified, and Streptococcus salivarius JIM8777. The PICRUSt functional annotation found differences in alanine, aspartate and glutamate metabolism (map00250), peptidoglycan (map00550), one carbon pool by folate (map00670), thiamine metabolism (map00730), and biosynthesis of amino acids (map01230) between the two groups. The results of the population validation study showed that the abundances of Enterobacter sp E.20 and Bacteroides massilience in the esophageal cancer group were increased, the abundance of Streptococcus salivarius JIM8777 was decreased, and the differences between the two groups were statistically significant (P<0.05). By establishing receiver operating characteristic analysis for representative species level biomarkers, the area under curve (AUC) of combining Enterobacter sp E.20, Streptococcus salivarius JIM8777, and Bacteroides massilience was 0.779, higher than single diagnosis (AUC=0.610, 0.608, and 0.659, respectively).

Conclusion There are significant differences in gut microbiota between the esophageal cancer group and the healthy control group. The combination of Enterobacter sp E.20, Streptococcus salivarius JIM8777, and Bacteroides Massilience has potential application value for the diagnosis of esophageal cancer.