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It has been shown that silica adsorbents can be used for adsorption of nizin from solutions obtained after centrifugation of the fermentation broth. The optimal structure of the adsorbent pores has been determined. Silica with pores 50 to 75 nm in size provided the highest adsorption rates. The value of silica adsorption of nizin depended on the medium pH. The maximum adsorption rates were observed at pH 6.5--7. At pH 3.5 the level of nizin adsorption was low.

The intensive biosynthesis of nizin on the glucose-yeast medium is observed during the logarithmic and early lag phases of the staphylococcal growth. The ratio of nizin in the fermentation broth (free nazin) and that bound with the cells depended on pH of the medium. When pH was maintained at 6.6-6.8, the amount of nazin in the cells during and growth logarithmic phase was equal to its amount in the fermentation broth filtrate. During the lag phase marked inactivation of nizin was noted. periodical feeding of casein prevented the nizin inactivation. The preliminary data are indicative of the enzymatic nature of the antibiotic.

Nizin is produced by Str. lactis, strain MSU. During biosynthesis it is excreted into the fermentation broth and gradually adsorbed on the organism cells. This was confirmed by experiments with an inactive variant of Str. lactis IIa. The cells of this culture adsorbed nizin from "active" fermentation broth. Adsorption of nizin depended on pH of the medium; at pH 2,3 the cells did not adsorbe the antibiotic and at pH 6.6 the amount of the antibiotic adsorbed by the cells was maximum.

A procedure for protoplasts of Str. lactis producing nisin was developed. The following lysing factors were used for obtaining the protoplasts: lycozyme, LE enzyme, lysosubtilin and an enzyme isolated from the culture fluid A. levoris. The use of the above factors in different combinations provided an increase in the number of the formed protoplasts from 1-2 in the field of the microscope vision to 15-20, which amounted to 25 per cent of the total number of the cells visible under microscope.

Some conditions for absorption of nisin, a polypeptide antibiotic by the cells of Str. lactis were studied. The amounts of nisin adsorbed by the cells depended on the culture age: at the late stationary phase the adsorption level was 2 times higher than that at the logarithmic phase. The cells grown on a "poor" medium adsorbed 85-90 per cent of nisin added to the solution, while the cells grown on the "rich" medium adsorbed 50 per cent of the antibiotic. The adsorption level of nisin by the cells subjected to a thermal shock was higher than that by the live cells. Desorption of nisin from the cells with acid ethanol and bivalent cation solutions was insignificant. Nisin is adsorbed by the cells of other microorganisms, the adsorption levels by the cells of Bac. brevis being the same as those by the streptococcal cells, while the levels adsorbed by Bac. polymyxa being 4 times lower.

To accelerate determination of nizin concentrations by the agar-diffusion method it is suggested that Twin-80 be added to the agar. For making the media composition more simple, agarized phosphate buffer, pH 5.0, or agarized water, pH 7.0, is recommended to be used for the lower layer.

Fermentative hydrolysates (FH) of the protein-vitamin complex (PVC) were used for the first time in media for cultivation of Str. lactis. It was found that the FH may be used in the media for cultivation of streptococci as a source of nitrogen instead of the yeast autolysate from baker's yeast and the level of nisin biosynthesis did not change. The replacement of the yeast autolysate by the FH is possible in both flasks with low volumes of the medium and 401 fermenters with 25 liters of the medium. The BVC FH is not a food raw material and its cost is low, which makes it advantageous.

The results of the study on optimization of the process of nisin isolation from the cultural liquid are presented. Different adsorbents, streptococcal cells, medium solid particles (biomass fermentalysates) and silica gel, were used for antibiotic adsorption.

The problem of microbial cell immobilization at present attracts the ever increasing attention of the scientists, since such organisms may be the source of various enzymes. Production of nizin by the immobilized cells of Str. lactis was studied. It was found that the cells of Str. lactis incorporated into polyacrylamide gel produced nizit on definite media. Still, the amount of the antibiotic was 2-3 times lower than in case of using free cells. The effect of a number of factors on the process of immobilization was studied and the influence of some factors, such as temperature, pH, aeration on nizin synthesis by the immobilized cells of the streptococcus was elucidated. Optimal conditions for nizin biosynthesis by the immobilized cells of Str. lactis were developed.

The effect of the initial pH value of the medium within 4.0 to 6.6 on the growth of Str. lactis and biosynthesis of nicin was studied. It was found that at the initial pH 4.0--4.5 of the medium the growth of the culture was poor, i.e. 11--14% of the control (initiral pH 6.6). With an increase in the value of the initial pH at least to 5.0 the growth of Str. lactis also increased. At the initial pH 4.0 no biosynthesis of nicin was observed. Under the experimental conditions the antibiotic synthesis by tr. lactic started at the initial pH being equal to 4.5 and reached its maximum at pH 6.6.

Immobilized cells of Streptococcus lactis, strain MSU, synthesized nisin by 20--30 per cent of the possible maximum antibiotic production level. The immobilized cells of the Streptococcus synthesized nisin by 40--50 per cent probably at the expense of the cell nutrient pools and by 50--60 per cent at the expense of the medium nutrient consumption. The electron microphotographs showed that the cells of Str. lactis, strain MSU, preserved their usual appearance in the granules of polyacrylamide gel 24 hours after immobilization. In 3 weeks there were observed structural changes in the cell wall and inner membranes resulting in the cell lysis after presence in the granules for 3 months.

Milk is the natural medium for Str. lactis, strain MSU. It is known that in winter and spring the growth and acid production by acidolactic streptococci are decreased. This is due, in particular, to the absence of vitamins in winter and spring milk. A number of vitamins present in complex natural products, such as tomato juice, milk and casein hydrolysates, beaf extract, etc. was studied with respect to their effect on the synthesis of nisin. The organic complexes had a positive effect on the growth of Str. lactis and the antibiotic biosynthesis. However, Str. lactis, strain MSU did not intensify the nisin synthesis on addition of vitamins to the spring skin milk. Possibly, lactis, strain MSU was of low sensitivity to the season of changes in milk.