ABSTRACT
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.
Subject(s)
Bacteriophage T4/growth & development , Tetrahymena/physiology , Tetrahymena/virology , Animals , Bacteriophage T4/ultrastructure , Bacteriophage lambda/growth & development , Capsid Proteins/metabolism , Coculture Techniques/methods , Isotope Labeling , Microscopy, Electron , Mutation , Sulfur Radioisotopes/metabolism , T-Phages/growth & development , Tetrahymena/genetics , Tetrahymena/ultrastructure , Tetrahymena thermophila/genetics , Tetrahymena thermophila/physiology , Tetrahymena thermophila/ultrastructure , Tetrahymena thermophila/virology , Virus InactivationABSTRACT
The nucleotide sequences of two self-splicing group I introns found in viruses that infect the eukaryotic green alga Chlorella were compared with those of 19 nuclear group I introns of 11 green algae, 1 red alga, 2 yeasts and 1 protist. The similarity ranging from 69.5% to 89.0% in any comparison strongly suggested a close relatedness of these introns. Since this kind of viruses infect algal cells residing in protists such as Paramecium, they may serve as a mediator to spread group I introns horizontally among organisms of different phylogenetic kingdoms.