Fecal Protease Activity Is Associated with Compositional Alterations in the Intestinal Microbiota

Ian M Carroll,Jennica P Siddle,Tamar Ringel-Kulka,Michael C Wu,Lionel Bueno,Yehuda Ringel,Laurent Ferrier,Benoit Foligne

doi:10.1371/journal.pone.0078017

Ian M Carroll, Jennica P Siddle + Show 6 more

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https://doi.org/10.1371/journal.pone.0078017

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Abstract

ObjectiveIntestinal proteases carry out a variety of functions in the gastrointestinal (GI) tract. Studies have reported that elevated enteric proteases in patients with GI disease can alter intestinal physiology, however the origin (human vs. microbial) of elevated proteases in patients with GI disease is unclear.AimThe aim of this study was to investigate the association between protease activity and the microbiota in human fecal samples.DesignIn order to capture a wide range of fecal protease (FP) activity stool samples were collected from 30 IBS patients and 24 healthy controls. The intestinal microbiota was characterized using 454 high throughput pyro-sequencing of the 16S rRNA gene. The composition and diversity of microbial communities were determined and compared using the Quantitative Insights Into Microbial Ecology (QIIME) pipeline. FP activity levels were determined using an ELISA-based method. FP activity was ranked and top and bottom quartiles (n=13 per quartile) were identified as having high and low FP activity, respectively.ResultsThe overall diversity of the intestinal microbiota displayed significant clustering separation (p = 0.001) between samples with high vs. low FP activity. The Lactobacillales, Lachnospiraceae, and Streptococcaceae groups were positively associated with FP activity across the entire study population, whilst the Ruminococcaceae family and an unclassified Coriobacteriales family were negatively associated with FP activity.ConclusionsThese data demonstrate significant associations between specific intestinal bacterial groups and fecal protease activity and provide a basis for further causative studies investigating the role of enteric microbes and GI diseases.

Highlights

Proteases, or proteolytic enzymes, catalyze the breakdown of proteins by hydrolysis of peptide bonds
Association of fecal protease (FP) activity with baseline demographic data revealed no confounding individual predictors (p=0.67). It has been known for some time that the intestinal microbiota is a significant source of protease activity in the GI tract, to date there has only been one report that correlated specific enteric bacterial taxa with FP activity in the human gut [26]
By analyzing the protease activity of representative enteric bacterial strains and human fecal samples it has previously been suggested that the activity of specific classes of proteases present in human feces are likely to originate from Bacteroides, Streptococcus, and Clostridium species [5]

Summary

Introduction

Proteolytic enzymes, catalyze the breakdown of proteins by hydrolysis of peptide bonds. The function of proteases was considered to be the breakdown of protein relevant to food digestion and intracellular protein turnover; it was discovered that precise cleavage of proteins by proteases leads to a very subtle means of regulation [2]. Proteolytic activity is tightly regulated to prevent any destructive activity of proteases. The enteric microbiota is a substantial source of serine, cysteine, and matrix metalloproteinases (MMPs) in the intestine [4,5,6]. This is exemplified by the reduction of colonic bacteria densities and protease activity by oral administration of antibiotics to mice [7]. Bacterial proteolytic activity in the intestine is reported to be ubiquitous and independent of inflammation [8]

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