Structure of vibriophage D10 tail sheath revealed by electron microscopy and computational image processing.

Vibriophage D10, a member of the Vibrio cholerae O-1El-Tor phage typing scheme, is used to detect the spread of the cholera epidemic and belongs to the Myoviridae family. The outer sheath of the tail of vibriophage is highly contractile in nature. We have used electron microscopy and computational image-processing techniques to determine the structure of this contractile tail sheath. The three-dimensional density map of the tail sheath reveals the presence of ∼35 Å long and ∼25 Å wide protrusions, extending out of the tail structure. The electron micrographs revealed that the tail sheaths of a considerable number of D10 phage particles undergo axial compression up to 51% at almost neutral pH (7.2) and at room temperature (20°). We find that the genome of the phage particles is ejected out when the tail sheath of the phage particles are deliberately made to contract by subjecting them to a surrounding environment of pH 10.5. We infer that the contraction of the tail sheath is responsible for the loss of the phage genome even at neutral pH and room temperature. This may be a plausible reason for the unusual behavior of rapid decline of the phage within a span of 48-72 h of its preparation.