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Gut microbiota can influence the feeding behavior of the host, but the underlying mechanisms are unknown. Recently, caseinolytic protease B (ClpB), a disaggregation chaperon protein of <i>Escherichia coli</i>, was identified as a conformational mimetic of &#945;-melanocyte-stimulating hormone (&#945;-MSH), an anorexigenic neuropeptide. Importantly, ClpB was necessary for <i>E. coli</i> to have an anorexigenic effect in mice, suggesting that it may participate in satiety signaling. To explore this further, we determined the short-term (2 h) effects of three macronutrients: protein (bovine serum albumin), carbohydrate (D-fructose) and fat (oleic acid), on the production of ClpB by <i>E. coli</i> and analyzed whether ClpB can stimulate the secretion of the intestinal satiety hormone, peptide YY (PYY). Isocaloric amounts of all three macronutrients added to a continuous culture of <i>E. coli</i> increased ClpB immunoreactivity. However, to increase the levels of ClpB mRNA and ClpB protein in bacteria and supernatants, supplementation with protein was required. A nanomolar concentration of recombinant <i>E. coli</i> ClpB dose-dependently stimulated PYY secretion from the primary cell cultures of rat intestinal mucosa. Total proteins extracted from <i>E. coli</i> but not from ClpB-deficient <i>E. coli</i> strains also tended to increase PYY secretion. These data support a possible link between <i>E. coli</i> ClpB and protein-induced satiety signaling in the gut.