Characterization of Fatty Acid Composition, Spore Germination, and Thermal Resistance in a Nisin-Resistant Mutant of Clostridium botulinum 169B and in the Wild-Type Strain

Abstract

ABSTRACT The membrane fatty acids, thermal resistance, and germination of a nisin-resistant (Nis r ) mutant of Clostridium botulinum 169B were compared with those of the wild-type (WT) strain. In the membranes of WT cells, almost 50% of the total fatty acids were unsaturated, but in those of Nis r cells, only 23% of the fatty acids were unsaturated. WT and Nis r spores contained similar amounts (approximately 23%) of unsaturated fatty acids, but the saturated straight-chain/branched-chain ratio was significantly higher in Nis r spores than in WT spores. These fatty acid differences suggest that Nis r cell and spore membranes may be more rigid, a characteristic which would interfere with the pore-forming ability of nisin. Nis r C. botulinum did not produce an extracellular nisin-degrading enzyme, nor were there any differences in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of coat proteins extracted from WT and Nis r spores, eliminating these as possible reasons for nisin resistance. Nis r spores had thermal resistance parameters similar to those of WT spores. In WT spores, but not in Nis r spores, nisin caused a 40% reduction in thermal resistance and a twofold increase in the germination rate. Because the nisin-induced increase in the germination rate of WT spores occurred only in the presence of a germinant (a molecule that triggers germination), nisin can be classified as a progerminant (a molecule that stimulates germination only in the presence of a germinant).