SummaryAll 47 non-nisin producing strains ofStreptococcus lactisand 12/13 strains ofStr. lactissubsp.diacetylactisexamined produced bacteriocins, for which the term lactostrepcins is suggested. Seven strains ofStr. cremorisexamined produced no bacteriocins active against 3 lactic streptococci strains used as indicators. The strains examined were divided into 3 groups: I, those producing lactostrepcins active against only one streptomycin resistant mutant ofStr. lactis60 indicator strain; II, those producing lactostrepcins active against all 3 indicator strains; III, those not producing lactostrepcins active against the indicator strains employed. The lactostrepcins were sensitive to various proteolytic enzymes and to phospholipase D, but retained full or partial activity after dialysis. Most of the bacteriocins studied were fully active only within the pH range 4·2–5·0 and were reversibly inactivated at pH 7·0 or 8·0. Results suggested occurrence of 4 different lactostrepcins. The lactostrepcins produced by all group I strains were the same, but there were differences among the lactostrepcins produced by group II strains. Lactostrepcins killed some β-haemolytic streptococci and some strains ofLactobacillus helveticus. One of the lactostrepcins was also active against certainLeuconostocstrains, but not against otherLeuconostocstrains, nor againstL. helveticusor other Gram-positive bacteria.
Rcwiiwl I 7 Decmibsr 1973 ; revised 2 I February I 974) S U M M A R Y 111 some nisin-producing strains of Streptococcus lactis, clones which were permanently incapable of producing nisin (Nis-) appeared spontaneously with a frequency of 0.03 to 0.82 : / ;. Treatment with proflavin (Pro), ethidium bromide (EB) or at a temperature of 40 "C increased the number of such clones. In one strain 78 :{ of cells became Nis-after treatment with Pro. Treatment with nitrosoguanidine did not reverse the effect of Pro or EB. There was no evidence that Pro or EB selected spontaneously-occurring Nis-clones. These observations suggest that the gene(s) responsible for nisin production in some S. lactis strains may be located on a plasmid, but further investigation is required to confirm this.
Eighty-seven strains of lactic streptococci (46 of Streptococcus lactis, 24 of S. diacetilactis, and 17 of S. cremoris) were tested for lysogeny; 12 S. lactis strains produced nisin. Lysogeny was found in five S. lactis strains (two of them were nisin producers) and in two S. diacetilactis strains. Four S. lactis and two S. diacetilactis lysogens liberated phages both spontaneously and after ultraviolet treatment, and one S. lactis strain liberated phages spontaneously only. No lysogens were found among the S. cremoris strains tested. An initial characterization of the lysogens and their phages was made. The lytic spectrum of some of the examined phages was very narrow (homospecific), whereas that of others was wide, including strains of the three investigated species.
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