Abstract
Abstract. Two bacteriophages (F5 and F6) were isolated from lysogenic Streptococcus bovis strains 46/2 and 59/2, respectively, after spontaneous induction. Both bacteriophages produced clear and small plaques (0.1–0.2 mm in diameter) on two host Streptococcus bovis strains (47/3 and 4/1) out of 12 tested. After UV-light induction, clear plaques of 1.0–1.2 mm in diameter were observed. Both bacteriophages were relatively resistant to chloroform, however, their survival in sterilised rumen fluid was not long because their complete inactivation was observed after 18 hours of cultivation in sterilised rumen fluid. Transmission electron microscopy showed great differences in the morphology of particles of these two bacteriophages. The F5 phage had an elongated slightly angular head, of a mean length of 94 nm and width of 50 nm, as well as a 180 nm long and 10–15 nm wide noncontractile flexible tail without a sheath. The bacteriophage F6 had an isometric head of icosahedral shape, 43 nm in diameter, and its noncontractile flexible tail without sheath was about 180–200 nm long and 10–12 nm wide. According to Ackermann's classification both phages belong to Siphoviridae. The genome sizes of both phages, determined by summing the molecular sizes of fragments generated by digestions with EcoRI, PstI, BglII and XbaI, were similar (about 41–43 kb). Restriction analysis of the genomes of these 2 bacteriophages by 8 restriction enzymes showed that SalI, BamHI and BspRI did not cleave the DNAs of these phages. Cleavage of the DNAs with the other five restriction enzymes showed a similar restriction pattern, however, with small differences. It is a curiosity to find two bacteriophages with the same genome size and relatively similar DNA restriction patterns having a different morphology of their capsids.
Highlights
The rumen ecosystem comprises a complex of dense microbial communities of bacteria, archaea, protozoa, fungi and bacteriophages (KLIEVE et al, 2004)
The lysogenic cultures releasing temperate bacteriophages were previously isolated from ruminal contents, the information of IVERSON and MILLIS (1976b) about 4% of lysogenic among Streptococcus bovis strains tested was at variance with the previous findings of TARAKANOV (1974), who reported that 47,9% of his ovine and 55,5% of his bovine S. bovis strains were lysogenic as well as with the published results of KLIEVE et al (1989) who obtained 23.7% lysogenic ruminal isolates
TARAKANOV (1974) endeavoured to confirm the assumption that an important source of bacteriophages in rumen are the lysogenic bacterial cultures. His experiments confirmed that lysogeny is widely distributed among the cultures of Streptococcus bovis inhabiting the rumen of ruminant animals and that bacteriophages are released from their host bacteria as spontaneously as after induction by UV-light or by chloroform
Summary
The rumen ecosystem comprises a complex of dense microbial communities of bacteria, archaea, protozoa, fungi and bacteriophages (KLIEVE et al, 2004). Phages lytic to ruminal bacteria were isolated from the rumen contents in low frequencies (IVERSON and MILLIS, 1976a; TARAKANOV, 1976). It suggests that the majority of phages in the rumen may exist in harmony with their hosts in a state of lysogeny or pseudolysogeny (KLIEVE and BAUCHOP, 1988) or the susceptible hosts may not yet have been found. To find a lysogenic strain, 12 Streptococcus bovis strains of our collection were tested for the spontaneous release of phage particles, they were treated by UV-light Both our bacteriophages (F5 and F6) in this paper described were spontaneously released by their host strains (46/2 and 59/2, respectively). The work presented here was directed to the comparison of some characteristics of these two ruminal bacteriophages
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