Abstract
Gluten is a cereal protein that is incompletely digested by human proteolytic enzymes that create immunogenic peptides that accumulate in the gastrointestinal tract (GIT). Although both environmental and human bacteria have been shown to expedite gluten hydrolysis, gluten intolerance is a growing concern. Here we hypothesize that together with food, we acquire environmental bacteria that could impact our GIT with gluten-degrading bacteria. Using in vitro gastrointestinal simulation conditions, we evaluated the capacity of endophytic bacteria that inhabit root vegetables, potato (Solanum tuberosum), carrot (Daucus sativus), beet (Beta vulgaris), and topinambur (Jerusalem artichoke) (Helianthus tuberosus), to resist these conditions and degrade gluten. By 16S rDNA sequencing, we discovered that bacteria from the families Enterobacteriaceae, Bacillaceae, and Clostridiaceae most effectively multiply in conditions similar to the human GIT (microoxic conditions, 37 °C) while utilizing vegetable material and gluten as nutrients. Additionally, we used stomach simulation (1 h, pH 3) and intestinal simulation (1 h, bile salts 0.4%) treatments. The bacteria that survived this treatment retained the ability to degrade gluten epitopes but at lower levels. Four bacterial strains belonging to species Bacillus pumilus, Clostridium subterminale, and Clostridium sporogenes isolated from vegetable roots produced proteases with postproline cleaving activity that successfully neutralized the toxic immunogenic epitopes.Key points• Bacteria from root vegetables can degrade gluten.• Some of these bacteria can resist conditions mimicking gastrointestinal tract.
Highlights
Gluten containing grains, especially wheat, are the main carbohydrate and plant protein sources in Western diets
In order to study how much the bacteria from root vegetables impact gluten degradation in human digestive tract, we set up an experiment taking into account the fact that peels of vegetables contain a considerably higher amount and diversity of bacteria than the inner pulp and that gluten hydrolysis starts in the human mouth and the majority is hydrolysed in the duodenum
Bacteria of vegetable origin from the genera Bacillus and Clostridium produce variable extracellular proteases that can efficiently hydrolase gliadin, and some of these proteases can destruct proline-rich peptides that are hardly digested by human proteolytic enzymes
Summary
Especially wheat, are the main carbohydrate and plant protein sources in Western diets. Due to the structure of proline, human gastric and pancreatic enzymes do not efficiently cleave the peptide bonds of proline-rich proteins and generate pathogenic peptides, which contribute to three types of human disorders: autoimmune celiac disease (CD), allergy to wheat, and non-celiac gluten sensitivity (NCGS) (van De Wal et al 1998; van de Wal et al 1999; ArentzHansen et al 2002). The prevalence of these three disorders has increased over the last two decades, which suggests an important environmental and/or lifestyle contribution to this susceptibility (Meijer et al 2018)
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