Nisin Production Research Articles

Functional properties of plasmids in lactic streptococci.

Plasmid biology has become an important area of investigation in dairy starter cultures since it now appears that some properties, vital for successful milk fermentations, are coded by genes located on plasmid DNA. Some of these metabolic properties observed in lactic streptococci have been clearly established as being plasmid-mediated. Examples would be lactose utilization and in Streptococcus lactis subsp. diacetylactis the ability to produce a bacteriocin-like substance. Phenotypic and physical evidence for plasmid linkage has been obtained for other traits such as citrate, sucrose, galactose, glucose, mannose, and xylose utilization, proteinase activity, modification/restriction systems, as well as for nisin production. Further genetic evidence is now needed to confirm plasmid association to these properties. For some characteristics the association with plasmids is highly speculative and is solely based on the phenotypic loss of a metabolic property. In this category would be sensitivity to agglutinins, sensitivity to the lactoperoxidase-thiocyanate-hydrogen peroxide inhibitory system, arginine hydrolysis, and slime production. Other properties which appear plasmid-mediated in lactic streptococci and which will be discussed include inorganic ion resistance, drug resistance, and diplococcin production.

Possible plasmid nature of the determinant for production of the antibiotic nisin in some strains of Streptococcus lactis.

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The effect of proflavin, ethidium bromide and an elevated temperature on the appearance of nisin-negative clones in nisin-producing strains of Streptococcus lactis.

SUMMARY In 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.

Activation of nisin production by UV-irradiation in a nisin-producing strain of Streptococcus lactis.

Isolierung von Mutanten mit erhohter Nisin-Produktion aus einem weiterenStreptococcus lactis-6 Stamm durch UV-Bestrahlung (9000 erg/mm2). Die Produktion des Antibiotikums nahm nach der ersten Bestrahlung im 50%, nach der zweiten Bestrahlung um 100% zu, wahrend nach der dritten eine Abnahme beobachtet wurde.

Lysogeny in lactic streptococci producing and not producing nisin.

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.

Lysogeny in Lactic Streptococci Producing and Not Producing Nisin

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.

The relation of the length of lag phase of growth to the synthesis of nisin and other basic proteins by Streptococcus lactis grown under different cultural conditions.

SUMMARY: A nisin-producing strain of Streptococcus lactis was grown in batch culture and at intervals during growth secondary cultures were derived from the parent culture and the length of lag of growth was estimated. Two media were used: a highly buffered ‘medium 22’ and an unbuffered (LTB) medium both without pH control and with pH controlled at about 6.7. In ‘medium 22’ the dry weight doubling time was 95 min. and at the end of growth the pH was 5.2. Neutralization of the culture in this medium did not markedly affect nisin production or dry weight. The total and cell-bound nisin formed/unit dry wt of organism tended to correlate with the length of lag phase of growth. In LTB medium the dry wt doubling time was 45 min. and the terminal pH was 4.5. Of the total nisin formed > 80% was in the culture fluid when the pH was allowed to decrease below 6.0; total nisin in cultures without pH control did not correlate with length of lag phase of growth. Neutralization of the culture increased the dry wt of organism about threefold. Neutralization also increased the cell-bound nisin/unit dry wt organism in stationary phase and the length of lag of growth of such organisms was longer than comparable stationary-phase organisms grown in unneutralized culture. Chloramphenicol (1 μg./ml. medium) decreased the nisin/unit dry wt organism at stationary phase and the length of lag of growth of such cultures was shorter than in comparable cultures without chloramphenicol. Frequently the start of growth was characterized by a decrease of bio-assayable nisin and a shortening of the lag phase; these changes could be mimicked by a culture which had reached the stationary phase through glucose depletion. The characteristics of early growth were reproduced after the addition of more glucose.

Biosynthesis of the Antibiotic Nisin and Other Basic Peptides by Streptococcus lactis Grown in Batch Culture

The fine structure of the membrane apparatus in obligate methanotrophic bacteria, Methylomonas methanica, Methylomonas rubrum 15 and Methylobacter bovis 53b was studied. Complex intracytoplasmic membrane systems of the I type were found in all cultures, but they differed by their structure and spatial organization depending on microorganisms. The cytoplasmic membrane was shown to be involved in the formation of complex membrane structures. A scheme of the spatial organization of the intracytoplasmic membrane systems on the basis of studying serial sections of the methanotrophs is suggested. The formation of the membranex packs is supposed to be a continuous process in Methylomonas methanica and Methylomonas rubrum but a discrete process in Methylobacter bovis.

Growth and nisin production of a strain of Streptococcus lactis.

SUMMARY: Stable mutant colonies were picked from a parent strain of Streptococcus lactis which gave improved yields of nisin; further improvement could not be produced by means of eolchicine or camphor. Nisin is stable in the culture fluid at acid pH values, but is inactivated by Seitz filtration or heating at pH 6 to 9. A ‘nisinase’ was not found. In the presence of sufficient glucose, growth was increased when the lactic acid formed was neutralized, the concentration of pantothenic acid becoming the limiting factor. Maximum nisin yields were obtained when, during fermentation in the presence of sufficient glucose and pantothenate at 23-30°, the pH was stabilized at c. 6, which is the pH optimum for nisin synthesis. Sodium lactate and nisin are only slightly inhibitory to the organism. Growth comes to an end because of the maximum limiting population density (‘M’-concentration) of cells, and is not due to the exhaustion of food or accumulation of toxic products.