title: Isolation and characterization of acid-sensitive mutants of Pediococcus acidilactici.
abstract: Acid-sensitive mutants of Pediococcus acidilactici BCC 9545, a starter culture of the Thai fermented pork sausage nham, were isolated as spontaneous neomycin resistant mutants. The mutants generally produced less acid and acidified the culture media less than the parent strain in a 72 h culturing period. Interestingly, the ATPase activities of the mutants did not differ considerably from that of the parent strain in acidic conditions. It was also found that the internal pH values of the mutant strains were somewhat lower in neutral environment, while at pH 5.0 their internal pHs were significantly lower compared to the parent's. Inhibiting the H(+)-ATPase activities in energized cells by N,N'-dicyclohexyl carbodiimide also revealed that protons were leaking from the mutants at neutral pH, which increased under acidic conditions. In contrast, the parent strain exhibited a smaller proton leak and only under acidic conditions. The membrane fatty acid analysis of the mutants indicated that under acidic conditions the mutants had a significantly smaller major unsaturated/saturated fatty acids ratio ((C(18:1)+C(18:3n6))/(C(16:0)+C(18:0))) compared to the parent strain's membrane. Taken together, these observations suggest there is a reasonable possibility that the membrane fatty acid profile differences in the mutants resulted in their acid-sensitivity.
authors.affiliation: Food Biotechnology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), 113 Paholyothin Road, Klong 1, Klong Luang, Pathumthani 12120, Thailand. peter.kur@biotec.or.th
authors.forename: Peter
authors.initials: P
authors.lastname: Kurdi
authors.forename: Thitapha
authors.initials: T
authors.lastname: Smitinont
authors.forename: Ruud
authors.initials: R
authors.lastname: Valyasevi
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D003257:Consumer Product Safety; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism; D005285:Fermentation; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008461:Meat Products / Q000382:microbiology*; D009154:Mutation; D010376:Pediococcus / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013552:Swine; D013785:Thailand
chemical_list: D005227:Fatty Acids; D006180:Proton-Translocating ATPases