The BaeSR Two-Component Regulatory System Mediates Resistance to Condensed Tannins in Escherichia coli

Abstract

The gene expression profiles of Escherichia coli strains grown anaerobically with or without Acacia mearnsii (black wattle) extract were compared to identify tannin resistance strategies. The cell envelope stress protein gene spy and the multidrug transporter-encoding operon mdtABCD, both under the control of the BaeSR two-component regulatory system, were significantly up-regulated in the presence of tannins. BaeSR mutants were more tannin sensitive than their wild-type counterparts.Condensed tannins, or proanthocyanidins, are common secondary metabolites of plants, consisting of flavonol polymers (17). High concentrations of tannins in fodder plants inhibit gastrointestinal bacteria (6,9,10,20) and reduce animal performance (9,18,21,23). Numerous mechanisms of how tannins may inhibit bacteria have been proposed, including tannin-polymer complexation, tannin-induced membrane disruption, and metal ion chelation (22). Despite the antimicrobial activities of tannins, many tannin-resistant bacteria have been isolated. However, the mechanisms behind this resistance are still unknown (22). Gram-negative bacteria may be less sensitive to the inhibitory effects of tannins, as gastrointestinal bacterial populations shifted toward gram-negative Enterobacteriaceae and Bacteroides species in rats fed diets containing 0.7 to 2.0% condensed tannins (20). There was a corresponding decrease in the gram-positive Clostridium leptum group. Escherichia coli is resistant to concentrations of up to 1% Acacia mearnsii (black wattle) tannin extract (WTE) under anoxic conditions. However, it was demonstrated to be sensitive to 0.1% under oxic conditions due to auto-oxidation of tannins resulting in hydrogen peroxide generation (19). To get insight into the mechanisms responsible for resistance to condensed tannins under anoxic conditions, we conducted a gene expression study to measure the total transcriptional responses of E. coli in the presence of WTE.The E. coli strains used in this study are described in Table 1. All growth experiments were performed with MOPS (3-morpholinopropane-1-sulfonic acid) medium (12), with glucose (0.4%) as the carbon source, and iron and trace elements were provided by trace element solution SL-10 (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany). MOPS medium was prepared, gassed with N 2 , and dispensed in an anaerobic chamber (Coy Laboratory Products, Ann Arbor, MI) under an atmosphere of 95% N 2 and 5% H 2 . Cysteinesulfide solution as a reducing agent was added to anaerobic medium (the final concentrations of L-cysteine ⅐ HCl and Na 2 S ⅐ 9H 2 O were 0.025%). WTE, an aqueous extract from Acacia mearnsii (black wattle) bark, was added to the MOPS medium at a final concentration of 1% (wt/vol). WTE contained 65.6% phenols as tannic acid equivalents and was donated by Wickett and Craig of America, Inc. (Curwensville, PA). WTE was filter sterilized before addition to growth medium. In order to identify specific transcriptional responses to the presence of tannins, as op...

Tannin-tolerant bacteria from crossbred Holstein x Zebu cows

“…The authors used dot-blot quantification to confirm that these Gram-negative bacterial groups predominated in the presence of dietary tannins, and that there was a corresponding decrease in the Gram-positive Clostridium leptum group and in other groups. Mechanisms for Gram-negative higher tolerance to tannins were suggested by Zoetendal et al (2008), which are beyond the scope of this study. In the present study, the Gram-negative isolates could not be identified, but both tolerated up to 2 g L -1 of tannins, and could not ferment cellulose or galactose.…”

Tannic Acid Inhibits Staphylococcus aureus Surface Colonization in an IsaA-Dependent Manner

“…Tannic acid has long been known to have antibacterial properties (42), bacteria are known to actively modulate gene expression in response to tannins (43,44), and recently, it has been suggested to have antibiofilm properties (45). Pentagalloyl glucose (one of the major components of commercial tannic acid) and ellagic acid (another plant-derived polyphenolic compound) have also been shown to inhibit biofilm formation in S. aureus (46,47).…”

Characterization of the Induction and Cellular Role of the BaeSR Two-Component Envelope Stress Response of Escherichia coli

“…Interestingly, flavonoids are closely related to condensed tannins, which were previously shown to be more toxic to a strain lacking BaeSR (44). To further test the ability of flavonoids to induce the BaeSR pathway, a number of structurally related compounds were chosen for testing.…”

“…In one, a phenotypic microarray found that a BaeSR mutant was more sensitive to growth in the presence of sodium tungstate, myricetin, gallic acid, and nickel chloride (43). A more recent study of global gene expression changes in the presence of plant secondary metabolites, called condensed tannins, discovered genes regulated by the Bae pathway to be upregulated in their presence (44). Zoetendal and colleagues also found that BaeSR mutants were more sensitive to growth in the presence of condensed tannins and that overexpression of the MdtABC efflux pump aided in survival under these conditions (44).…”

“…A more recent study of global gene expression changes in the presence of plant secondary metabolites, called condensed tannins, discovered genes regulated by the Bae pathway to be upregulated in their presence (44). Zoetendal and colleagues also found that BaeSR mutants were more sensitive to growth in the presence of condensed tannins and that overexpression of the MdtABC efflux pump aided in survival under these conditions (44). These studies suggest novel inducing cues of the BaeSR pathway, and also that induction of the MdtABC efflux pump may be a major means by which the BaeSR pathway mediates adaptation to these compounds.…”