Tubular bacteriophage heads were observed in the lysate of two phages from Streptococcus lactis obtained from single plaques without mutagenesis. The frequency of appearance of the tubular heads was 2.5 and 16%. Aberrant structures have been observed among phages active on numerous bacterial species: Escherichia coli (11), Bacillus mycoides (23), Bacillus thuringiensis (5) , Streptococcus faecalis (4), Streptococcus thermophilus (M. S. Reddy, Ph.D. thesis, University of Iowa, Ames, 1974),

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... lococcus aureus (3) , Lactobacillus lactis and Lactobacillus bulgaricus (2), and Streptomyces venezuelae (12). Genetic determination of such structures has been well studied by using E. coli phages T4 and A mutants (9, 11, 15, 19) to elucidate the mechanisms of virus assembly (9, 13, 14, 20) . Despite many studies (17, 18, 21, 24; J. A. Nyiendo, Ph.D. thesis, Oregon State University, 1975) on the morphology of phages active on lactic streptococci of group N (Streptococcus cremoris, Streptococcus lactis, and S. lactis subsp. diacetylactis), only Bradley (7) observed the presence of particles with heads twice the length of those of a normal phage of S. lactis. In the course of a study on the morphology of phages active on lactic streptococci, we observed in two instances particles resembling polyheads of E. coli phages. The two phages, 25 and 160, were isolated from cheese whey in French factories in which slowness of acidification was encountered. The propagating strains of the phages were S. lactis Z261 and S. lactis A311, respectively. They belong to two different host range groups (g2 for phage 160 and g4 for phage 25) (8). Both had a narrow host range (8 and 10 strains, respectively). The technique of Accolas and Spillmann (1) was used to prepare the phages. Clear lysates containing about 109 PFU/ml were obtained from inoculating one plaque into M17 broth (22). Lysates were cooled and diluted (1/3) in chilled distilled water (4°C) and then sedimented at 100,000 x g for 90 min at 4°C. After ultracentrifugation, pellets were allowed to resuspend in 1 ml of sterile chilled 0.1 M ammonium acetate for at least 4 h. Suspensions were then negatively stained with phosphotungstic acid or uranyl acetate by the agar diffusion method of Anderson and Doane (6) , which allowed a better recovery of phages as compared with the simple adhesion method (10). Observations were performed with a Zeiss EM 10A electron microscope. Tubular head frequencies were determined on approximately 300 particles. Fifteen phages were measured on prints at high magnification (x 320,000). Magnification was monitored with catalase crystals (25). Phages 25 and 160 usually possessed a prolate head of 65 by 48 and 66 by 46 nm, respectively. The noncontractile tails, bearing cross striations, were 90 and 107 nm, respectively ( Fig. 1A and D). Terminal structures on the tail have not been observed. The phages did not seem to possess a collar. Tubular heads were observed in the lysate of phage 25 at a frequency of 2.5%. Their dimensions reached 56 by 902 nm, i.e., 14 times the length of a normal head (Fig. 1C) . Most of the tubular heads were four to five times longer than normal phage heads, but a sufficient number of measurements for a length histogram was not obtained. A lattice-like structure on some tubular heads (Fig. 1A) resembling some lambda tubular heads (16) was observed. Some tailed tubular heads, roughly four times the length of a normal head and tail, were also noted (Fig. 1B) . The presence of an isolated tail about 360 nm in length was also noted. The lysate of phage 160 also contained tubular heads (Fig. 1E) . Some appeared partially filled. They were present at a frequency of 16% and were occasionally observed as aggregates (Fig. 1E) . Their dimensions varied, and the tubular heads reached 11 times the length of a normal head. The length distribution for phage 25 could not be established. It appeared, however, that tubular heads are three to eight times longer than heads of normal phages. No tailed tubular heads were observed for phage 25. We conclude from the present study that the mechanism of morphogenesis of the head and the tail might be susceptible to alterations in prolate lactic streptococci phages. The tubular 294 on May 7, 2020 by guest http://aem.asm.org/ Downloaded from