Genetic Variation of the SusC/SusD Homologs from a Polysaccharide Utilization Locus Underlies Divergent Fructan Specificities and Functional Adaptation in Bacteroides thetaiotaomicron Strains

Dietary polysaccharides play a dominant role in shaping the composition and functionality of our gut microbiota. Dietary interventions using these microbiota-accessible carbohydrates (MACs) serve as a promising tool for manipulating the gut microbial community. However, our current gap in knowledge regarding microbial metabolic pathways that are involved in the degradation of these MACs has made the design of rational interventions difficult. The issue is further complicated by the diversity of pathways observed for the utilization of similar MACs, even in closely related microbial strains. Our current work focuses on divergent fructan utilization pathways in two closely related B. thetaiotaomicron strains and provides an integrated approach to characterize the molecular basis for strain-level functional differences.Genomic differences between gut-resident bacterial strains likely underlie significant interindividual variation in microbiome function. Traditional methods of determining community composition, such as 16S rRNA gene amplicon sequencing, fail to capture this functional diversity. Metagenomic approaches are a significant step forward in identifying strain-level sequence variants; however, given the current paucity of biochemical information, they too are limited to mainly low-resolution and incomplete functional predictions. Using genomic, biochemical, and molecular approaches, we identified differences in the fructan utilization profiles of two closely related Bacteroides thetaiotaomicron strains. B. thetaiotaomicron 8736 (Bt-8736) contains a fructan polysaccharide utilization locus (PUL) with a divergent susC/susD homolog gene pair that enables it to utilize inulin, differentiating this strain from other characterized Bt strains. Transfer of the distinct pair of susC/susD genes from Bt-8736 into the noninulin using type strain B. thetaiotaomicron VPI-5482 resulted in inulin use by the recipient strain, Bt(8736-2). The presence of the divergent susC/susD gene pair alone enabled the hybrid Bt(8736-2) strain to outcompete the wild-type strain in vivo in mice fed an inulin diet. Further, we discovered that the susC/susD homolog gene pair facilitated import of inulin into the periplasm without surface predigestion by an endo-acting enzyme, possibly due to the short average chain length of inulin compared to many other polysaccharides. Our data builds upon recent reports of dietary polysaccharide utilization mechanisms found in members of the Bacteroides genus and demonstrates how the acquisition of two genes can alter the functionality and success of a strain within the gut

Glucose sensor-augmented continuous subcutaneous insulin infusion in patients with diabetic gastroparesis: An open-label pilot prospective study

<div><p>Erratic blood glucose levels can be a cause and consequence of delayed gastric emptying in patients with diabetes. It is unknown if better glycemic control increases risks of hypoglycemia or improves hemoglobin A1c levels and gastrointestinal symptoms in diabetic gastroparesis. This study investigated the safety and potential efficacy of continuous subcutaneous insulin infusion (CSII) and continuous glucose monitoring (CGM) in poorly controlled diabetes with gastroparesis. Forty-five type 1 or 2 patients with diabetes and gastroparesis and hemoglobin A1c >8% from the NIDDK Gastroparesis Consortium enrolled in a 24 week open-label pilot prospective study of CSII plus CGM. The primary safety outcome was combined numbers of mild, moderate, and severe hypoglycemic events at screening and 24 weeks treatment. Secondary outcomes included glycemic excursions on CGM, hemoglobin A1c, gastroparesis symptoms, quality-of-life, and liquid meal tolerance. Combined mild, moderate, and severe hypoglycemic events occurred similarly during the screening/run-in (1.9/week) versus treatment (2.2/week) phases with a relative risk of 1.18 (95% CI 0.85–1.64, P = 0.33). CGM time in hypoglycemia (<70 mg/dL) decreased from 3.9% to 1.8% (P<0.0001), time in euglycemia (70–180 mg/dL) increased from 44.0% to 52.0% (P = 0.02), time in severe hyperglycemia (>300 mg/dL) decreased from 14.2% to 7.0% (P = 0.005), and hemoglobin A1c decreased from 9.4±1.4% to 8.3±1.3% (P = 0.001) on CSII plus CGM. Symptom scores decreased from 29.3±7.1 to 21.9±10.2 with lower nausea/vomiting, fullness/early satiety, and bloating/distention scores (P≤0.001). Quality-of-life scores improved from 2.4±1.1 to 3.1±1.1 (P<0.0001) and volumes of liquid nutrient meals tolerated increased from 420±258 to 487±312 mL (P = 0.05) at 24 weeks. In conclusion, CSII plus CGM appeared to be safe with minimal risks of hypoglycemic events and associated improvements in glycemic control, gastroparesis symptoms, quality-of-life, and meal tolerance in patients with poorly controlled diabetes and gastroparesis. This study supports the safety, feasibility, and potential benefits of improving glycemic control in diabetic gastroparesis.</p></div

Study design for GLUMIT-DG.

<p>The study design is shown. After an initial screening phase (up to 3 visits over up to 8 weeks), a run-in phase (up to 4 visits over up to 8 weeks) was conducted. The formal treatment phase consisted of 6 study visits over 24 weeks when CSII and CGM were used together to optimize glycemic control.</p

Characteristics of glycemic excursions.

<p>Characteristics of glycemic excursions.</p

Primary safety outcome during screening/run-in vs. treatment phases—Weekly combined mild, moderate, and severe hypoglycemic episodes.

<p>Primary safety outcome during screening/run-in vs. treatment phases—Weekly combined mild, moderate, and severe hypoglycemic episodes.</p