FUNGI COMMUNITY WITHIN COLORECTAL NEOPLASIA AND ITS CONTRIBUTION TO COLORECTAL CARCINOGENESIS

Background and Aims: The relationship between intratumoral fungi and the progression of colorectal cancer (CRC) is largely unclear. We aim to determine the structure of the fungal community within a neoplasia (adenoma or CRC) and its association with genetic mutation in adenoma and CRC.
Methods: A total of 261 tissue biopsies from two different region cohorts of CRC patients (n = 21) and adenoma patients (n = 21) (2-5 tissue biopsies from adenoma or CRC and 1-2 biopsies from adjacent normal tissues per individual) were collected. Microbial profiling was performed using 18S ribosomal RNA gene sequencing with subsequent investigation of microbiota diversities and heterogeneity. Correlations between microbiota dysbiosis and host genetic alterations (KRAS mutations and microsatellite instability) were also analysed in all tumour biopsy samples. In addition, intra-kingdom network was established to elucidate the relationship of bacterial and fungi.
Results: In two cohorts, alpha and beta diversity analyses showed significant differences between CRC and adenoma. We analysed the fungi composition in each cohort to generate an overview of individual microbiota profile at phylum level. The abundance of Basidiomycota was increased in CRC compared with adenoma, while Ascomycota was decreased in CRC. We then discovered that fungal communities within neoplasia were heterogeneous, with significant intra-neoplasia variation in abundance (e.g, Malassezia and Aspergillus). Moreover, we found that the intra-neoplasia variation in abundance of individual microbes changed along the adenoma–carcinoma sequence. At the fungal genus level, 11 fungus (e.g, Malassezia, Aspergillus,Candida, and Anopheles) were enriched in CRCs and 1 fungi (Collapsidium) was depleted in CRC compared to adenoma, which was verified in the second cohort. There was a significant difference in intra-neoplasia microbiota (e.g, Hanseniaspora, Saccharomyces and Debaryomyces) between biopsies with and without KRAS mutation (P<0.05) or microsatellite instability (P<0.05), indicating the association of intratumoral microbial heterogeneity with host genetic alteration. Multi-domain networks showed that the link between fungi and bacteria was progressively stronger according to adenoma–carcinoma sequence. Cooccurrence interactions between fungi and bacteria, mostly contributed by fungal Ascomycota and bacterial Proteobacteria in CRC, while Malasseziaceae and Aspergillaceae acted as crucial hubs.
Conclusions: This study provides an intra-neoplasia fungal profile of CRC carcinogenesis and explored the intra-neoplasia fungal dysbiosis with the host genetic alteration. We also revealed the fungi and bacteria interplay in contributing to CRC progression.