Purpose To investigate whether there are differences in diversity, taxonomic composition, and predicted functional pathways of the gut microbiome between Island Hispanic Puerto Ricans (HPR) and mainland non-Hispanic whites (NHW) measured before and at the end of chemo-radiation (CRT) for Rectal Cancer. Methods Fifty-six stool samples of newly diagnosed rectal cancer patients (25 HPR and 31 NHW) were amplicon-sequenced during chemo-radiotherapy. 16S rRNA gene data was analyzed using QIIME2, phyloseq, and LEfSe. Results We observed similar within-sample alpha diversity for HPR and NHW participants during CRT. However, at the end of CRT, several taxa were present at significantly different abundances across both groups. Taxa enriched in the gut of HPR compared to NHW included Muribaculaceae, Prevotella 2 and 7, Gemella, Bacillales Family XI, Catenibacterium, Sutterella, Pasteurellales, and Pasteurellaceae genera, whereas over-represented taxa in NHW participants were Turicibacter and Eubacteriaceae. Significant differences in predicted HPR microbiota functions included pathways for synthesis of L-methionine and degradation of phenylethylamine and phenylacetate. Conclusion In this pilot study, taxonomic analyses and functional predictions of the gut microbiomes suggest greater inflammatory potential in gut microbial functions among HPR rectal cancer patients undergoing CRT compared to that of NHW participants.
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