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

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).