Abstract
Blastocystis is the most prevalent protist of the human intestine, colonizing approximately 20% of the North American population and up to 100% in some nonindustrialized settings. Blastocystis is associated with gastrointestinal and systemic disease but can also be an asymptomatic colonizer in large populations. While recent findings in humans have shown bacterial microbiota changes associated with this protist, it is unknown whether these occur due to the presence of Blastocystis or as a result of inflammation. To explore this, we evaluated the fecal bacterial and eukaryotic microbiota in 156 asymptomatic adult subjects from a rural population in Xoxocotla, Mexico. Colonization with Blastocystis was strongly associated with an increase in bacterial alpha diversity and broad changes in beta diversity and with more discrete changes to the microbial eukaryome. More than 230 operational taxonomic units (OTUs), including those of dominant species Prevotella copri and Ruminococcus bromii, were differentially abundant in Blastocystis-colonized individuals. Large functional changes accompanied these observations, with differential abundances of 202 (out of 266) predicted metabolic pathways (PICRUSt), as well as lower fecal concentrations of acetate, butyrate, and propionate in colonized individuals. Fecal calprotectin was markedly decreased in association with Blastocystis colonization, suggesting that this ecological shift induces subclinical immune consequences to the asymptomatic host. This work is the first to show a direct association between the presence of Blastocystis and shifts in the gut bacterial and eukaryotic microbiome in the absence of gastrointestinal disease or inflammation. These results prompt further investigation of the role Blastocystis and other eukaryotes play within the human microbiome. IMPORTANCE Given the results of our study and other reports of the effects of the most common human gut protist on the diversity and composition of the bacterial microbiome, Blastocystis and, possibly, other gut protists should be studied as ecosystem engineers that drive community diversity and composition.
Highlights
Blastocystis is the most prevalent protist of the human intestine, colonizing approximately 20% of the North American population and up to 100% in some nonindustrialized settings
We did not identify any individuals infected by Crysptosporidium parvum or Giardia intestinalis but did observe coinfection with Entamoeba histolytica/E. dispar in five individuals, who were excluded from the bioinformatics analysis in order to assess the effect of Blastocystis only
The intestinal microbiota is highly variable among individual humans, and its diversity is affected by factors like diet, sociogeographic setting, antibiotic use, disease, age, and to a lesser degree, genetics [24, 27, 48]
Summary
Blastocystis is the most prevalent protist of the human intestine, colonizing approximately 20% of the North American population and up to 100% in some nonindustrialized settings. Recent reports in humans suggest that Blastocystis is associated with compositional and diversity differences of the bacterial gut microbiota [2, 7, 34] Given that this protist is known to cause disease in certain individuals and that the reported results are confounded by disease status, it remains unknown whether the changes in bacterial microbiomes are due to the presence of Blastocystis or to ongoing inflammation. Through this investigation, we detected marked taxonomic and functional bacterial differences associated with asymptomatic colonization of Blastocystis that support its role as a common eukaryotic gut commensal that drastically influences the bacterial microbiota through currently unknown mechanisms
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