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Abiotic factors are thought to be primarily responsible for the loss of bacteriophages from the environment, but ingestion of phages by heterotrophs may also play a role in their elimination. Tetrahymena thermophila has been shown to ingest and inactivate bacteriophage T4 in co-incubation experiments. In this study, other Tetrahymena species were co-incubated with T4 with similar results. In addition, T. thermophila was shown to inactivate phages T5 and lambda in co-incubations. Several approaches, including direct visualization by electron microscopy, demonstrated that ingestion is required for T4 inactivation. Mucocysts were shown to have no role in the ingestion of T4. When (35)S-labeled T4 were fed to T. thermophila in a pulse-chase experiment, the degradation of two putative capsid proteins, gp23(*) and hoc, was observed. In addition, a polypeptide with the apparent molecular mass of 52 kDa was synthesized. This suggests that Tetrahymena can use phages as a minor nutrient source in the absence of bacteria.

Tetrahymena has been shown to ingest and inactivate bacteriophages, such as T4, in co-incubation experiments. In this study, Tetrahymena thermophila failed to inactivate phages PhiX174 and MS2 in co-incubations, although PhiX174 were ingested by T. thermophila, as demonstrated by: (1) recovery at defecation in a pulse-chase experiment, (2) recovery from Tetrahymena by detergent lysis, and (3) transmission electron microscopy. We conclude, therefore, that the phages must be digestion-resistant. Internalized PhiX174 were further shown to be partially protected from lethal damage by ultraviolet (UV) C and UVB irradiation. Finally, ingested PhiX174 were shown to be rapidly transported through buffer in a horizontal swimming, race tube-like assay. The transport and protection of phages may confer evolutionary advantages that explain the acquisition of digestion-resistance by some phages.

There is a growing need for engineered tissues in a wide variety of medical applications and as alternatives to animal tissues for in vitro toxicology testing. While techniques for the preparation of a variety of synthetic tissue constructs have been devised, little attention has been focused upon the optimum conditions necessary for storage and shipping of these tissue devices. This study investigates the effects of hypothermic storage on synthetic human epidermis (EpiDerm, MatTek Corp., Ashland, MA) and specifically examines the quality of storage in keratinocyte growth medium (KGM), a standard skin culture medium, compared with storage in HypoThermosol, a new hypothermic preservation solution. EpiDerm samples were immersed in HypoThermosol for 1 to 13 days at 4 degrees C and were assayed using the noninvasive, viability indicator dye, Alamar Blue (AB). Samples immersed for 1 to 9 days in HypoThermosol retained their viability subsequent to warming to 37 degrees C and for at least 7 days thereafter in culture. During this time samples previously stored in HypoThermosol continued to generate a stratum corneum and their ultrastructural characteristics were similar to EpiDerm that were not exposed to hypothermic solutions. This profile, however, was not apparent in EpiDerm maintained for 1 to 13 days in KGM and subsequently warmed. These samples appeared viable immediately upon warming in most cases, but viability was not retained thereafter. EpiDerm maintained in KGM and allowed to recover at 37 degrees C appeared necrotic and failed to continue to differentiate. The conclusions of this study are the following: (1) HypoThermosol protects the viability of EpiDerm during cold-storage, (2) HypoThermosol preserves EpiDerm's ability to differentiate subsequent to warming, and (3) the inferior preservation of samples stored in KGM was most apparent 24 h after warming.

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