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Mutagenesis of Strains of Propionibacterium to Produce Cold-Sensitive Mutants¹

Department of Food Technology, Iowa State University, Ames 50011

ABSTRACT

A mutagenesis procedure that involved exposures to N-methyl-N '-nitro-N-nitro-soguanidine followed by penicillin counterselection was developed to obtain cold-sensitive mutants of strains of Propionibacterium commonly used for production of Swiss cheese. Optimum conditions for mutagenesis were exposure to 150 µg/ml N-methyl-N'-nitro-N-nitro-soguanidine for 30 min at 32°C to kill approximately 99.0% of the cells, followed by exposure to 2000 µg/ml penicillin G at 14°C for 48 h to select for those organisms unable to grow at low temperature. Seven cold-sensitive mutants were found that grew at rates similar to that of the parent at 32°C but grew much more slowly than the parent 14°C. All mutants behaved identically to the parent strain in tests to determine sugar fermentations and nitrate reduction. Three of the cold-sensitive mutants differed from the parent strain in sensitivity to streptomycin, which suggests they may contain altered ribosomes.

¹ Journal Paper Number J-10758 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project Number 2487.

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