Our gut microbiota provides us with many benefits; defending us against pathogens, tuning our immune systems, and aiding in the digestion of fiber. Now scientists have discovered yet another way that the bacteria in our guts could help by offering a potential way of protecting us from chemical modifications of food ingredients introduced by food processing.
Researchers at the Washington University School of Medicine in Saint Louis Missouri have discovered a species of gut bacteria that can transform the harmful byproducts of food processing into less harmful byproducts in mice and in vitro conditions. Specifically, scientists have found that the bacteria Collinsella intestinalis can metabolize the Maillard Reaction Product (MRP) e-fructoselysine (FL) to innocuous products.
Maillard reaction products form upon heat-induced reaction of amino acids with reducing sugars and are common in processed foods. The consumption of MRPs has dramatically increased in recent years due to the processing and “ultra-processing” of foods and are associated with negative health effects such as diabetes and cardiovascular disease.
To conduct this experiment, scientists used mice that were colonized with a defined group of 54 sequenced and cultured human gut bacterial strains. After a model gut community was established, mice were given defined sugar-rich (mainly sucrose) diets containing either whey protein isolate, as a representative of processed dietary protein, or an amino acid (AA) mixture that matched the composition of the whey protein isolate as a control.
Scientists found that the absolute abundance of Collinsella intestinalis in the fecal microbiota of mice was on average 3.4-fold higher in animals consuming the whey diet compared to those consuming the AA diet. This gut-dwelling bacterium utilized FL as a carbon source in a dose-dependent fashion. The effect was selective, as dietary whey protein did not increase the absolute abundance of Collinsella aerofaciens, although both species were able to catabolize FL in vitro. The repression of FL utilization locus by glucose in the diet in C. aerofaciens but not in C. intestinalis may partly explain these findings.
Next, authors wanted to determine whether the genes involved in the import and metabolism of FL in C. intestinalis was different between the whey and AA diet groups. Using microbial ribonucleic acid sequencing, authors were able to determine that 73 genes exhibited statistically significant differences in their expression between the two diet treatments. The upregulated genes were primarily located at a single genomic locus that encode genes involved in the utilization of FL/glucoselysine.
Thus, the putative machinery for importing and phosphorylating FL are all upregulated in C. intestinalis in the whey diet compared to the AA diet. The authors suspect that this upregulation of FL-related genes drives the increase in C. intestinalis absolute abundance by enabling C. intestinalis growth on FL derived from whey. In support of this, authors report that C. intestinalis is able to import and metabolize FL in vitro, leading to excretion of lysine, formate, and acetate that are innocuous metabolic end products of glycolysis.
Overall, authors conclude that C. intestinalis fitness increases in the presence of FL because C. intestinalis is able to utilize this protein modification as a carbon source. They suggest that in the future, at risk populations may be considered as candidates for well-controlled clinical studies where they are given candidate strains capable of bioremediating harmful components of their diets generated by food processing.
Wolf, Ashley R., Darryl A. Wesener, Jiye Cheng, Alexandra N. Houston-Ludlam, Zachary W. Beller, Matthew C. Hibberd, Richard J. Giannone, et al. 2019. “Bioremediation of a Common Product of Food Processing by a Human Gut Bacterium.” Cell Host and Microbe 26 (4): 463-477.e8. https://doi.org/10.1016/j.chom.2019.09.001 .