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.
Subject(s)
Cell Membrane/metabolism , Meat Products/microbiology , Mutation , Pediococcus , Proton-Translocating ATPases/metabolism , Animals , Consumer Product Safety , Fatty Acids/analysis , Fatty Acids/metabolism , Fermentation , Food Handling/methods , Food Microbiology , Humans , Hydrogen-Ion Concentration , Pediococcus/classification , Pediococcus/genetics , Pediococcus/isolation & purification , Pediococcus/metabolism , Proton-Translocating ATPases/antagonists & inhibitors , Swine , ThailandABSTRACT
Eight strains of aerobic, spore-forming, Gram-positive, moderately halophilic bacteria were isolated from sauce (nam-pla and bu-du) produced in Thailand by the fermentation of fish. They grew optimally in the presence of 10 % NaCl, at 37 degrees C and pH 7.0. A diagnostic diamino acid, meso-diaminopimelic acid, was present in the cell-wall peptidoglycan. The predominant menaquinone was MK-7. The major cellular fatty acids were anteiso-C(15 : 0) and iso-C(16 : 0). Phosphatidylglycerol, diphosphatidylglycerol and an unidentified glycolipid were found to be the major polar lipid components. The DNA G+C content was 42-43 mol%. These bacteria were further divided into two groups based on phenotypic characteristics and DNA-DNA similarities. Three strains of Group I were highly affiliated to the type strain of Lentibacillus salicampi in terms of phenotypic characterization and DNA-DNA similarities (96-102 %); accordingly, they were identified as strains of L. salicampi. A representative strain of Group II, strain IS40-3T, was most closely related to L. salicampi in terms of 16S rRNA-based phylogenetic analysis, although five strains of Group II could be distinguished from L. salicampi by means of several phenotypic properties, low 16S rRNA gene sequence similarity (95.2 %) and low DNA-DNA similarities (12-32 %). Therefore, the Group II strains should be included in a novel species of the genus Lentibacillus, for which the name Lentibacillus juripiscarius sp. nov. is proposed. The type strain is IS40-3T (=JCM 12147T=PCU 229T=TISTR 1535T).
