Bacterial Culture Preservation in Frozen and Dry-Film Methylcellulose

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Abstract
Of 61 bacterial cultures, including strains of Pseudomonas, Xanthomonas, Erwinia, Agrobacterium, Corynebacterium, Serratia, Klebsiella and Escherichia, 47 remained viable after storage in frozen methylcellulose or in dried methylcellulose for up to 38 mo. Pathogenicity remained intact for the strains tested. Bacteria were grown on a solid medium, removed and placed in 1.0% methylcellulose (cellulose methyl ether) to make a final suspension of 108 colony-forming units (CFU)/ml. For storage in dried form the bacteria-methylcellulose suspension was placed in a petri dish and dried in a forced-air incubator. After 24 h of storage at 25.degree. C, viable populations of 105 CFU/mg (equivalent to 106 CFU/ml) were recovered. Populations of 102 to 104 CFU/mg were recovered after storage of up to 38 mo. Similar results were obtained in frozen methylcellulose. Survival was greatly enhanced when the growth medium for the bacteria was potato dextrose peptone rather than nutrient agar, yeast dextrose calcium carbonate peptone or King''s medium B. Addition of 0.1 M MgSO4 to the methylcellulose suspension and to the resuspending liquid also increased survival and recovery from storage for some strains. Methylcellulose storage should be a simple, inexpensive and reliable method of maintaining cultures for short or long periods of time.