An In Vitro Model of the Horse Gut Microbiome Enables Identification of Lactate-Utilizing Bacteria That Differentially Respond to Starch Induction

Abstract

Laminitis is a chronic, crippling disease triggered by the sudden influx of dietary starch. Starch reaches the hindgut resulting in enrichment of lactic acid bacteria, lactate accumulation, and acidification of the gut contents. Bacterial products enter the bloodstream and precipitate systemic inflammation. Hindgut lactate levels are normally low because specific bacterial groups convert lactate to short chain fatty acids. Why this mechanism fails when lactate levels rapidly rise, and why some hindgut communities can recover is unknown. Fecal samples from three adult horses eating identical diets provided bacterial communities for this in vitro study. Triplicate microcosms of fecal slurries were enriched with lactate and/or starch. Metabolic products (short chain fatty acids, headspace gases, and hydrogen sulfide) were measured and microbial community compositions determined using Illumina 16S rRNA sequencing over 12-hour intervals. We report that patterns of change in short chain fatty acid levels and pH in our in vitro system are similar to those seen in in vivo laminitis induction models. Community differences between microcosms with disparate abilities to clear excess lactate suggest profiles conferring resistance of starch-induction conditions. Where lactate levels recover following starch induction conditions, propionate and acetate levels rise correspondingly and taxa related to Megasphaera elsdenii reach levels exceeding 70% relative abundance. In lactate and control cultures, taxa related to Veillonella montpellierensis are enriched as lactate levels fall. Understanding these community differences and factors promoting the growth of specific lactate utilizing taxa may be useful to prevent acidosis under starch-induction conditions.

Faecal parameters as biomarkers of the equine hindgut microbial ecosystem under dietary change

“…Those authors found a particularly high increase of the relative abundance of Veillonella sp. which is a lactateutilizing bacteria genus (Biddle et al, 2013). In the current study faecal LPS concentration was positively correlated with the lactate-utilizing bacteria count in the proximal hindgut.…”

Polysaccharide Utilization Loci: Fueling Microbial Communities

“…Likewise, the mechanisms by which regulatory systems within Bacteroidetes PULs respond to carbohydrates and how signals are transduced into gene expression are not fully understood. In particular, a complete structural and functional portrait of these complex membrane-spanning systems, as well as a detailed understanding of the genetic signatures targeted by these proteins (135), will help fill a significant gap in our understanding of how PULs are regulated and may help usher in an era of designer communities and personalized intestinal medicine (136)(137)(138). Recently, a series of cisencoded small RNAs were discovered in association with a subset of PULs in Bacteroides fragilis (139).…”

Adhesion of Lactobacillus reuteri strain Lr1 to equine epithelial cells and competitive exclusion of Clostridium difficile from the gastro-intestinal tract of horses

“…High blood lactate levels may lead to acidosis, a phenomenon associated with irritated or damaged mucosa (Al Jassim et al 2005). Acidosis often leads to laminitis, which is symptomatic of toxins secreted from the GIT into the blood stream (Biddle et al 2013) or colic (Pagan 1998), but this is usually associated with blood glucose concentrations in excess of 200 mg dl −1 (Thrall et al 2004). …”