title: Amino acids improve acid tolerance and internal pH maintenance in Bacillus cereus ATCC14579 strain.
abstract: This study investigated the involvement of glutamate-, arginine- and lysine-dependent systems in the Acid Tolerance Response (ATR) of Bacillus cereus ATCC14579 strain. Cells were grown in a chemostat at external pH (pH(e)) 7.0 and 5.5. Population reduction after acid shock at pH 4.0 was strongly limited in cells grown at pH 5.5 (acid-adapted) compared with cells grown at pH 7.0 (unadapted), indicating that B. cereus cells grown at low pH(e) were able to induce a marked ATR. Glutamate, arginine and lysine enhanced the resistance of unadapted cells to pH 4.0 acid shock of 1-log or 2-log populations, respectively. Amino acids had no detectable effect on acid resistance in acid-adapted cells. An acid shock at pH 4.0 resulted in a marked drop in internal pH (pH(i)) in unadapted cells compared with acid-adapted cells. When acid shock was achieved in the presence of glutamate, arginine or lysine, pH(i) was maintained at higher values (6.31, 6.69 or 6.99, respectively) compared with pH(i) in the absence of amino acids (4.88). Acid-adapted cells maintained their pH(i) at around 6.4 whatever the condition. Agmatine (a competitive inhibitor of arginine decarboxylase) had a negative effect on the ability of B. cereus cells to survive and maintain their pH(i) during acid shock. Our data demonstrate that B. cereus is able to induce an ATR during growth at low pH. This adaptation depends on pH(i) homeostasis and is enhanced in the presence of glutamate, arginine and lysine. Hence evaluations of the pathogenicity of B. cereus must take into account its ability to adapt to acid stress.
authors.affiliation: INRA, UMR408 Sécurité et Qualité des Produits d'Origine Végétale, F-84914 Avignon, France.
authors.forename: Khadidja
authors.initials: K
authors.lastname: Senouci-Rezkallah
authors.forename: Philippe
authors.initials: P
authors.lastname: Schmitt
authors.forename: Michel P
authors.initials: MP
authors.lastname: Jobin
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000596:Amino Acids / Q000378:metabolism* / Q000494:pharmacology; D001120:Arginine / Q000378:metabolism / Q000494:pharmacology; D001409:Bacillus cereus / Q000187:drug effects / Q000254:growth & development*; D002262:Carboxy-Lyases / Q000378:metabolism* / Q000494:pharmacology; D003257:Consumer Product Safety; D003470:Culture Media; D005506:Food Contamination / Q000517:prevention & control; D005516:Food Microbiology; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D003470:Culture Media; D018698:Glutamic Acid; D001120:Arginine; D002262:Carboxy-Lyases; D008239:Lysine