Shape shifter: redirection of prolate phage capsid assembly by staphylococcal pathogenicity islands

Staphylococcus aureus pathogenicity islands (SaPIs) are molecular parasites that hijack helper phages for their transfer. SaPIbov5, the prototypical member of a family of cos type SaPIs, redirects the assembly of ϕ12 helper capsids from prolate to isometric. This size and shape shift is dependent on the SaPIbov5-encoded protein Ccm, a homolog of the ϕ12 capsid protein (CP). Using cryo-electron microscopy, we have determined structures of prolate ϕ12 procapsids and isometric SaPIbov5 procapsids. ϕ12 procapsids have icosahedral end caps with Tend = 4 architecture and a Tmid = 14 cylindrical midsection, whereas SaPIbov5 procapsids have T = 4 icosahedral architecture. We built atomic models for CP and Ccm, and show that Ccm occupies the pentameric capsomers in the isometric SaPIbov5 procapsids, suggesting that preferential incorporation of Ccm pentamers prevents the cylindrical midsection from forming. Our results highlight that pirate elements have evolved diverse mechanisms to suppress phage multiplication, including the acquisition of phage capsid protein homologs.

Control of Brochothrix thermosphacta Spoilage of Pork Adipose Tissue Using Bacteriophages†

Adipose tissue discs were coinoculated with Brochothrix thermosphacta and homologous bacteriophages (phages) to determine the effects these had on phage multiplication, bacterial growth, and off-odor development during storage at 2°C or under simulated retail display at 6°C. In the presence of about 105 bacteria/cm2 and an equivalent number of phages, there was a 3-log increase in phage numbers and a 2-log decrease in bacterial numbers, and objectionable off-odors were suppressed during refrigerated storage. Up to 68% of the surviving bacterial population were resistant to phages. The storage life of adipose tissue could be increased from 4 days in controls to 8 days in phage-treated samples by preventing the development of off-odors associated with the growth of B. thermosphacta. Phages may provide a novel approach to extending the storage quality of chilled meats.

Multiplication Characteristics of FRNA Phage and Its Utility as an Indicator for Pathogenic Viruses

The possibility of multiplication of F-specific RNA phage (FRNA phage) multiplication in the environment was investigated. Using the Qβ strain in pure culture as a model FRNA phage, the effects of bacterial growth phase, substrate concentration and cultivation temperature on phage multiplication were studied. Similar experiments with environmental samples from raw sewage were then preformed.

Isolation and partial characterization of a bacteriophage active on Hyphomicrobium sp. WI-926

Isolation of a Hyphomicrobium phage from raw sewage from Athens, Ohio, was achieved by a combination of differential centrifugation, filtration, enrichment in mixed Hyphomicrobium cultures, and purification on individual host strains by subculturing single plaques in soft agar overlayers. Enrichments with water from Lake Erie and Lake Beechwood (Ohio) were unsuccessful. Out of 21 Hyphomicrobium strains and 22 other Gram-negative and Gram-positive bacteria tested, only Hyphomicrobium WI-926 (isolated from a German forest pond) was susceptible. This phage had an isometric head (diameter between opposite apices, 67 nm) and a short (12 nm), noncontractile tail and belongs thus to the morphogroup C1. It contained double-stranded DNA. The single-step growth curve showed a latent period of 9 h, a rise period of 6 h, and a burst size of 35. The various differentiation stages in the host development exhibited different affinities for phage adsorption and development. While all stages allowed phage adsorption, the daughter cells were most efficient. Phage multiplication was limited to daughter cells, and the development of infected swarmer cells was arrested permanently at this stage.

Temperature-sensitive mutation. IV. Induction and characterization of a ts-mutation in RNA-containing bacteriophage R17

Temperature-sensitive mutants of the RNA phage R17 were induced by treatment with 10−5 M 5-fluorouracil. One of the temperature-sensitive mutants, ts24, was studied and the following facts were discovered: (1) ts24 undergoes eclipse at the non-permissive temperature, 43 °C. (2) If the temperature is increased to non-permissive levels before 60 min of postinfection culture, phage multiplication ceases. (3) At 43 °C, ts24 cannot synthesize progeny viral RNA. (4) Upon decreasing the temperature to permissive levels during the first 60 min of postinfection culture, RNA replication resumes almost instantaneously. It was concluded from these facts that ts24 contains a temperature-sensitive mutation in the RNA replicating function.

Some new results in the mathematical theory of phage-reproduction

SummaryIn the theory of phage reproduction, the mathematical models considered thus far (see Gani [5]) assume that the bacterial burst occurs a fixed time after infection, after a fixed number of generations of phage multiplication, or when the number of mature bacteriophages has reached a fixed threshold. In the present paper, a more realistic assumption is considered: given that until timetthe bacterial burst has not taken place, its occurence betweentandt+ Δtis a random event with probabilityf(· |t)Δt+o(Δt), wherefis a non-negative and non-decreasing function of the numberX(t) of vegetative phages and ofZ(t), the number of mature bacteriophages at timet.More specifically it is assumed thatf=b(t)X(t) +c(t)Z(t) withb(t),c(t) ≦ 0. HereX(t) denotes the survivors in a linear birth and death process andZ(t) the number of deaths until timet.The joint distribution ofXTandZT, the respective numbers of vegetative and mature bacteriophages at the burst time is considered. The distribution ofZTis then fitted to some observed data of Delbrück [2].

Transduction of Streptococcus pyogenes K 56 by Temperature-Sensitive Mutants of the Transducing Phage A 25

Experiments aimed at increasing the efficiency of transduction by the virulent group A streptococcal phage A 25 were carried out using temperature-sensitive phage mutants. Lysates of phages carrying ts mutations proved to transduce more efficiently than wild type lysates, the order of increasing effectiveness being ts+ < tsl ~ ts2 < tsl — 2. Differential survival of the recipient, K 56, appeared to be the principal reason for the improvement of transduction when cells decapsulated by hyaluronidase were transduced at the restrictive temperature. In transduction of encapsulated recipient cells, in which the superiority of ts lysates was less pronounced, the possibility was considered that mutant lysates might contain higher fractions of transducing particles than wild type lysates produced under parallel conditions.The transducing activity of wild type lysates depended strongly on the temperature at which the phage had multiplied on the donor strain, the frequency of transduction increasing with decreasing temperature. Since the minimal latent period of the phage varied roughly in the same way with temperature, a connection is suggested between the time required for phage multiplication and the proportion of transducing particles formed.

Some new results in the mathematical theory of phage-reproduction

Summary In the theory of phage reproduction, the mathematical models considered thus far (see Gani [5]) assume that the bacterial burst occurs a fixed time after infection, after a fixed number of generations of phage multiplication, or when the number of mature bacteriophages has reached a fixed threshold. In the present paper, a more realistic assumption is considered: given that until time t the bacterial burst has not taken place, its occurence between tand t + Δt is a random event with probability f(· | t)Δt + o(Δt), where f is a non-negative and non-decreasing function of the number X(t) of vegetative phages and of Z(t), the number of mature bacteriophages at time t. More specifically it is assumed that f = b(t)X(t) + c(t)Z(t) with b(t), c(t) ≦ 0. Here X(t) denotes the survivors in a linear birth and death process and Z(t) the number of deaths until time t. The joint distribution of XT and ZT , the respective numbers of vegetative and mature bacteriophages at the burst time is considered. The distribution of ZT is then fitted to some observed data of Delbrück [2].