Characterization of the invasion process of an exogenous single strain into colonic micrbiota in vitro

Humans ingest many microorganisms, which may invade and interact with the resident microbiota. However, extensive knowledge about those microbe-microbe interactions without host factor is lacking. Here, we investigated such invasion process, using a derivative of the model probiotic Lactiplantibacillus plantarum WCFS1, into different in vitro gut microbiota continuously cultivated in the intestinal PolyFermS fermentation model. L. plantarum successfully colonized and organized itself spatially in the planktonic and sessile fraction of chicken, human infant and adult microbiota. Carrying capacity was independent of L. plantarum introduction dose and second supplementation. The two adult microbiota dominated by Prevotella and Ruminoccocus exhibited a higher carrying capacity than the two dominated by Bacteroides with 105 and 103 CFU L. plantarum/ml effluent, respectively. Cultivation of human adult microbiota over three months resulted in decreased carrying capacity and correlated positively with richness and evenness, suggesting enhanced resistance towards invaders. Our analyses ultimately allowed the identification of valerate as modulator to increase the carrying capacity in a microbiota-independent manner. Obtained data demonstrate the suitability of the PolyFermS in vitro model, mimicking both planktonic and sessile cell growth, to gain a deeper ecological understanding of the invader-microbiota interactions, which is highly relevant to develop microbiome manipulations and probiotic strategies.