Icosahedral Head Research Articles

Isolation and properties of a Pseudomonas acidovorans bacteriophage.

SUMMARY The lytic bacteriophage ϕW-14 was isolated from sewage using Pseudomonas acidovorans no. 14 as host. The phage had an icosahedral head some 85 nm. in diameter and a contractile tail some 140 nm. long. ϕW-14 formed plaques on only a few strains of P. acidovorans. The phage gave biphasic absorption kinetics, with an adsorption constant of 1·9 × 10−9 ml./min. The latent period was 60 min. and the burst size was about 300. The burst size was dependent upon culture age. The k u.v.. for inactivation of ϕW-14 was 4·35 min.−1. P. acidovorans was shown to possess a potent photoreactivating system. The heat of inactivation of ϕW-14 was calculated to be 75,700 cal./mole. The phage gave biphasic thermal inactivation kinetics at 55° and 60° but not at 65°. The phage mutated spontaneously to a different plaque type. This mutation affected the adsorptive properties, the thermal sensitivity and the burst size of the phage.

Bacteriophages of Clostridium saccharoperbutylacetonicum

The fine structure of phage HM 2 (group I) active on Clostridium saccharoperbutylacetonicum was studied by an electron microscopy with a negative-staining technique, and compared with those of more conventional types, phages HM 3 (group II) and HM 7 (group III), whose tails were clearly observed by a shadow-casting technique. This study revealed that phage HM 2 had an intricate tail which was not observed by a shadow-casting technique. Phage HM 2 has an icosahedral head about 450Å in diameter and a non-contractile tail about 300Å long. The distal 130Å of the tail axis has a width of 80Å which is wider than the upper portion of the tail (50 to 60Å). The distal enlargement is not seen in the hollow tail. Twelve fibrous-shaped appendages are attached symmetrically at the upper portion of tail axis and extend toward the distal base of the tail. Their length is a little shorter than 300Å. They combine with divalent cations in the phage dilution medium, and also adsorb the host cell debris. Phage HM 3 has an icosahedral head about 770Å in diameter and a tail about 1000Å long and 150Å wide with contractile sheath. Phage HM 7 has an icosahedral head about 750Å in diameter and a long non-contractile tail about 2000Å long and about 120Å wide with forked tip. The structure of the tail of phage HM 2 is quite different from those of phages HM 3 and HM 7 hitherto described and those of the various phages of other bacteria.

Some properties of bacteriophages active on the obligate anaerobe Clostridium sporogenes

The most commonly encountered bacteriophages active on Clostridium sporogenes have elongated six-sided heads and simple, tubular, noncontractile tails. These viruses have minimum latent periods of about 1 hour at 37° and yield average burst sizes from 17 to 150 PFU/cell. Phage F1 was selected as typical of this group and has been characterized in these studies. F1-directed DNA synthesis begins 20 minutes after infection, and the first mature intracellular virus particles are formed in 40 minutes. Infected cells begin to lyse 60 minutes after infection, and lysis is complete within 90 minutes. F1 particles sedimented with an S obs. of 301, and were composed of 40% protein and 60% DNA. The DNA gave a thermal denaturation profile typical of double-stranded DNA with a T M value of 85.2°. This indicates a 39.5% GC content which is somewhat higher than 33.2% GC found for its host, C. sporogenes 213. Two other viruses, active on strains of C. sporogenes but encountered less frequently, were a very large phage 420 mμ in length with an icosahedral head and a noncontractile tail, and a temperate phage with a smaller icosahedral head and a tail with a contractile sheath. All these viruses were similar to phages described for aerobic, gram-positive bacteria.

Mitomycin C induction of a temperate phage in Pseudomonas aeruginosa.

After addition of mitomycin C to Pseudomonas aeruginosa strain MAC-264 cells, DNA synthesis stops but resumes again after 45 min. This resumption in DNA synthesis is due to the induction of a temperate phage. Early after induction, both RNA and protein syntheses continue but later on little or no net synthesis of these macromolecules occurs. Cell lysis occurs at 90 to 105 min after addition of mitomycin C. Analysis of the lysates indicates that a DNA phage with an icosahedral head about 55 mμ in diameter with a short wedge-shaped tail is produced. This phage [Formula: see text] has a buoyant density of 1.468 g/ml in CsCl. The guanine + cytosine content of the phage DNA determined by its buoyant density in CsCl is 46% compared to 68% for the host DNA.Some phage tail-like structures which have a buoyant density of 1.305 g/ml in CsCl are also induced at the same time.

THE FINE STRUCTURE OF LACTOBACILLUS BACTERIOPHAGES.

Twelve phages isolated from sewage and active on lactobacilli were examined by electron microscopy with a negative-staining technique. Those phages active on Lactobacillus fermenti (heterofermentative) possess icosahedral heads and sheathed tails which end in base-plates and pins. Those phages active on Lactobacillus casei (homofermentative) differ in that their heads are octahedral or icosahedral and they possess collars. The overall length of all the phages is similar and their base-plates remain attached to the sheaths when these contract. No tail fibres were seen. A temperate Lactobacillus fermenti phage was also examined. It has a small hexagonal head and a long unsheathed tail which ends in a star-shaped structure.

THE STRUCTURE OF BACTERIOPHAGE SP8.

The structure of the large Subtilis bacteriophage SP8 has been studied by electron microscopy. Capsomeres have been resolved in the icosahedral head. The structural changes occurring in the act of triggering the tail are discussed.