High-molecular-weight polymers from dietary fiber drive aggregation of particulates in the murine small intestine

Abstract

The lumen of the small intestine (SI) is filled with particulates: microbes, therapeutic particles, and food granules. The structure of this particulate suspension could impact uptake of drugs and nutrients and the function of microorganisms; however, little is understood about how this suspension is re-structured as it transits the gut. Here, we demonstrate that particles spontaneously aggregate in SI luminal fluid ex vivo. We find that mucins and immunoglobulins are not required for aggregation. Instead, aggregation can be controlled using polymers from dietary fiber in a manner that is qualitatively consistent with polymer-induced depletion interactions, which do not require specific chemical interactions. Furthermore, we find that aggregation is tunable; by feeding mice dietary fibers of different molecular weights, we can control aggregation in SI luminal fluid. This work suggests that the molecular weight and concentration of dietary polymers play an underappreciated role in shaping the physicochemical environment of the gut.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Interplay of motility and polymer-driven depletion forces in the initial stages of bacterial aggregation

“…To ensure we selected biologically relevant physical parameters for our experiments, we used data from our previous gel permeation chromatography experiments on luminal fluid from the murine small intestine to determine the range of the polymer molecular weights and concentrations. 1 In these previous experiments, the polymers we found in the murine small intestine ranged in size from a few kDa to a few MDa. 1 Therefore, we chose to tune the depletion potential in this work with polymers within this size range.…”

“…1 In these previous experiments, the polymers we found in the murine small intestine ranged in size from a few kDa to a few MDa. 1 Therefore, we chose to tune the depletion potential in this work with polymers within this size range. As our test polymer, we chose to use PEG solutions in a motility buffer (MB, 0.1 mM EDTA, 10 mM potassium phosphate, pH 7.0).…”

“…4 For example, in the gut, polymers are secreted by the host [5][6][7][8] and dietary fibers are ingested regularly. 1 In wastewater treatment plants, sludge used to collect microbes and particulate waste also contains polymers. 9,10 Polymers are well known to aggregate bacteria, which is important because aggregation precedes biofilm formation, 11 correlates with altered gene expression, 3,12 including antibioticresistance genes, 13 and induces phenotypic changes such as quorum sensing.…”

“…Furthermore, the initial stages of aggregation are particularly relevant for biological systems where the system may never reach steady state; for example, in the gastrointestinal (GI) tract where food and ingested material are constantly in transit. 1,25 In these environments, aggregate formation is constantly disrupted because of shear, peristaltic contractions, and other forces, making early aggregate formation relevant to these biological systems.…”

“…We quantify this experimentally by using confocal fluorescence microscopy to measure the size distribution of bacterial aggregates in PEG solutions with molecular weights and concentrations relevant to the murine small intestine. 1 Furthermore, we develop an understanding of which physical parameters influence the initial formation of these aggregates. We use a physical model for motile bacteria in PEG solutions that focuses on the balance of depletion and swim forces as well as the effective diffusivity of the bacteria.…”