Curing experiments were performed on Lactobacillus helveticus strain ATCC 15009 in order to find a correlation between the presence of three extrachromosomal elements and specific phenotypic traits. Mitomycin C treatment of the strain was found to result in an appearance of slow-coagulation variants unable to coagulate milk in 24 h at 42 °C. The effect of mitomycin C on phenotypic and genotypic characteristics of L. helveticus was therefore further examined. The presence of mitomycin C appeared to act on the proteolytic system of the strain: slow variants exhibited a poor casein breakdown (50 % less) compared with the parental strain. Aminopeptidase activity and lactose utilization were unaffected. The phenotypic variation is possibly due to a point mutation of genetic patrimony. No loss of plasmid DNA was detected after mitomycin C treatment and the restriction pattern of plasmid and chromosomal DNA of the variants, after digestion with several restriction endonucleases, was identical to that obtained for the parental strain.
Slow Milk Coagulating Variants of Lactobacillus helveticus / Fortina, M. G.; Rossi, P.; Mora, D.; Parini, C.; Neviani, E.. - In: FOLIA MICROBIOLOGICA. - ISSN 0015-5632. - 41:1(1996), pp. 33-38. [10.1007/BF02816337]
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