(566c) In vitro Fermentation to Understand Healthy and Stressed Gut Microbiome Metabolism

The abundant bacterial consortia within the gut microbiome plays a critical role in metabolism of dietary compounds that translate to beneficial influences on the host. From a military perspective, the gut microbiome serves as an ideal tool to not only enhance Soldier gut and immune health, but also improve survivability and performance. Our work employs in vitro fermentation as a means to elucidate the systematic processes of colonic bacterial metabolism of dietary inputs under both native and stressed conditions. The broad experimental capacity of in vitro fermentation enables the generation of multi-faceted data sets (i.e time- and dose-dependent, colonic domain specific, etc.) to gain a detailed understanding on bacterial community dynamics, inflammation and immunity.  This talk will focus on the use of in vitro fermentation to investigate both the prebiotic potential of cranberry A-type proanthocyanidins (PAC) within a healthy microbiome, and the utilization of fermentable fiber and protein as a function of stress-induced dysbiosis on gut metabolism. Briefly, fecal inocula derived from three individuals was used to inoculate a nutrient-rich anaerobic media supplemented with purified PAC. Colonic fermentations were performed in parallel at 37^oC under colonic domain-specific condtions using an automated bioreactor platform for precise control over a multitude of parameters. Total growth assessment through protein content analyses revealed domain-specific metabolism. After 5 hrs, PAC caused a 2.3-fold increase in total bacterial abundance under transverse colon conditions while ascending and distal colon showed 1.7 and 1.3 fold increase respectively. After 10 hrs, further PAC metabolism was not evident in ascending and distal colons; however, was still evident under transverse conditions until stationary phase was met. Bacterial population dynamics, determined through 16S rRNA sequencing, metabolic byproduct analysis via GC-FID and PAC metabolite discovery through LC/MS is underway. These analyses will enable identification of specific bacteria and the upregulation of certain SCFAs that collectively result in a beneficial health effect on the host. For stressed metabolism studies, fecal samples from volunteers exposed to an acute military-relevant stressor, a sudden change in diet for 21 consecutive days, were pooled (N=10) and inoculated in a nutrient-rich medium supplemented with resistant starch (RS II) or casein, at multiple dosages. Total growth, population and SCFA analysis for comparison to the pre-intervention microbiome state and to volunteers on a standard diet (N=10) will be discussed. Efforts to simulate the gut microbiome using continuous culture fermentation will also be presented. An understanding of gut microbiota metabolism dynamics under both stressed and unstressed conditions could direct future dietary supplementation strategies to build resiliency against military-relevant stressors and offset negative health and performance impacts of gut dysbiosis.