Bacteriophages of methanotrophic bacteria have been found in 16 out of 88 studied samples (underground waters, pond water, soil, gas and oil installation waters, fermentor cultural fluids, bacterial paste, and rumen of cattle) taken in different geographic zones of the Soviet Union. Altogether, 23 phage strains were isolated: 10 strains that specifically lysed only Methylosinus sporium strains, 2 strains that each lysed 1 of 5 Methylosinus trichosporium strains studied, and 11 strains that lysed Flavobacterium gasotypicum and, at the same time, 1 M. sporium strain. By fine structure, the phages were divided into two types (with very short or long noncontractile tails); by host range and serological properties, they fell into three types. One-step growth characteristics of the phages differed only slightly; the latent period varied from 6 to 8 h, the rise period varied from 4 to 6 h, and the average burst size was 100. All phages had guanineand cytosinerich double-stranded deoxyribonucleic acid consisting of common nitrogen bases. The molecular mass of the deoxyribonucleic acid as determined by restriction endonuclease analysis was 29.4 x 106 for M. sporium phages and 44 x 106 for F. gasotypicum phages. By all of the above-mentioned properties, all phages within each of the groups were completely identical to one another, but differed from phages of other groups. Bacteriophages lysing M. sporium and M. trichosporium GB2 were identical to phages Ml and M4, respectively, which were isolated earlier in the German Democratic Republic on the same methanotrophic species.

Bacteriophages of methanotrophic bacteria were isolated from 67 fish. Only two phages isolated from two fish species specifically lysed Methylocystis sp. and Flavobacterium gasotypicum. The phages lysing these species were designated 63-F and CMF-1-F, respectively. The isolated phages differed greatly in the fine structure of the virion, plaque morphology, spectrum of lytic action, serological properties, and UV sensitivity. At the same time, they had identical one-step growth characteristics: their latent period equalled 5 h, lysis time was 3 to 4 h, and burst size was about 240 virions. The phages had guanineand cytosine-rich double-stranded DNAs consisting of common nitrogen bases. The molecular masses of the DNAs as determined by the sums of restriction endonuclease cleavage fragments were 28 x 106 daltons for phage 63-F and 31 x 106 daltons for phage CMF-1-F.

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The threat of cholera spread beyond the borders of endemic countries and the realness of the emergence of introduced epidemic foci remain the actual problems and neccessitate continuous development of specific prophylaxis of this disease. The review is dedicated to the analysis of the effectiveness of licensed cholera vaccines as well as to possible perspectives of the advancement of cholera specific prophylaxis.