Oral microbiota disorder in GC patients revealed by 2b-RAD-M

Abstract

Background: Microbiota alterations are linked with gastric cancer (GC). However, the relationship between the oral microbiota (especially oral fungi) and GC is not known. In this study, we aimed to apply 2b-RAD sequencing for Microbiome (2b-RAD-M) to characterize the oral microbiota in patients with GC.

Methods: We performed 2b-RAD-M analysis on the saliva and tongue coating of GC patients and healthy controls. We carried out diversity, relative abundance, and composition analyses of saliva and tongue coating bacteria and fungi in the two groups. In addition, indicator analysis, the Gini index, and the mean decrease accuracy were used to identify oral fungal indicators of GC.

Results: In this study, fungal imbalance in the saliva and tongue coating was observed in the GC group. At the species level, enriched Malassezia globosa (M. globosa) and decreased Saccharomyces cerevisiae (S. cerevisiae) were observed in saliva and tongue coating samples of the GC group. Random forest analysis indicated that M. globosa in saliva and tongue coating samples could serve as biomarkers to diagnose GC. The Gini index and mean decreases in accuracy for M. globosa in saliva and tongue coating samples were the largest. In addition, M. globosa in saliva and tongue coating samples classified GC from the control with areas under the receiver operating curve (AUCs) of 0.976 and 0.846, respectively. Further ecological analysis revealed correlations between oral bacteria and fungi.

Conclusion: For the first time, our data suggested that changes in oral fungi between GC patients and controls may help deepen our understanding of the complex spectrum of the different microbiotas involved in GC development. Although the cohort size was small, this study is the first to use 2b-RAD-M to reveal that oral M. globosa can be a fungal biomarker for detecting GC.

Keywords: 2b-RAD-M; Biomarker; Gastric cancer; Oral fungi.

Fig. 1

Comparison of salivary bacteria between gastric cancer patients and healthy controls. A Shared and unique species between the two groups shown by Venn diagram. B Comparison of alpha diversity (Chao1, Shannon index, and Simpson index) between the two groups. C Comparison of beta diversity (Bray–Curtis distance, Binary Jaccard distance and Euclidean distance) between the two groups. D The relative abundance and distribution of salivary bacteria at the phylum, genus, and species levels. E The top 10 species with different abundances between the two groups

Fig. 2

Salivary fungal diversity, abundance, and distribution in the two groups. A Comparison of salivary fungal alpha diversity between the two groups based on Chao1, Shannon index, and Simpson index. B Comparison of salivary fungal beta diversity (Bray–Curtis distance, binary Jaccard distance and Euclidean distance) between the two groups. C, D The LEfSe results identified the most divergent fungal taxa in the two groups and scored the two groups of saliva samples by LDA. The brightness of each point was proportional to the size of its effect. E The relative abundance of the salivary fungal phyla, the top 15 most abundant genera, and species is represented in the bar plot

Fig. 3

Salivary M. globose has a strong indication ability for GC. A The indicator analysis showed the ability of M. globosa to be an indicator of GC. B, C Both the mean decrease accuracy and the Gini index of salivary M. globosa were the largest. D Salivary M. globosa achieved an area under the receiver operating characteristic curve (AUC) of 0.976 for the classification of the GC group from the control group

Fig. 4

Tongue coating fungi diversity, abundance, and distribution in the two groups. A Comparison of tongue coating fungal alpha diversity between the two groups based on Chao1, Shannon index, and Simpson index. B Comparison of tongue coating fungal beta diversity (Bray–Curtis distance, binary Jaccard distance and Euclidean distance) between the two groups. C, D The LEfSe method identified the most divergent fungal taxa in the two groups and scored the two groups of tongue coating samples by LDA. The brightness of each point was proportional to the size of its effect. E The relative abundance of the tongue coating fungal phyla, the top 15 most abundant genera, and species is represented in the bar plot

Fig. 5

Tongue coating M. globosa has a strong indicator ability for GC. A The indicator analysis showed the ability of tongue coating M. globosa as an indicator of GC. B, C Both the mean decrease in accuracy and the Gini index of tongue coating M. globosa were the largest. D Tongue coating M. globosa achieved an area under the receiver operating characteristic curve (AUC) of 0.846 for the classification of the GC group from the control group

Fig. 6

Perturbed intrakingdom and interkingdom ecological networks in gastric cancer (GC). The chord diagram of salivary fungi and bacteria with the greatest difference in relative abundance at the phylum level in the GC group (A) and the control group (B). The chord diagram of tongue coating fungi and bacteria with the greatest difference in relative abundance at the phylum level between the GC group (C) and the control group (D)