Only little information is available on a particular class of Myoviruses, the SPO1-like
bacteriophages infecting low
G+C Gram-positive host
bacteria (
Firmicutes). We present the genome analysis and molecular characterization of the large,
virulent, broad host-range
Listeria phage A511. A511 contains a unit (informational) genome of 134,494 bp, encompassing 190 putative
open reading frames and 16 tRNA genes, organized in a modular fashion common among the
Caudovirales.
Electron microscopy,
enzymatic fragmentation analyses and
sequencing revealed that the A511
DNA molecule contains redundant, linear
terminal repeats of 3,125 bp length, encompassing nine small putative ORFs. This particular genome structure explains why A511 is unable to perform general transduction. A511 features significant sequence homologies to
Listeria phage P100 and other morphologically related
phages infecting Firmicutes, such as
Staphylococcus phage K and
Lactobacillus phage LP65. Equivalent but more extensive
terminal repeats also exist in
phages P100 ( approximately 6 kb) and K ( approximately 20 kb).
High resolution electron microscopy revealed, for the first time, the presence of
long tail fibers in these
viruses, organized in a six-fold symmetry. Mass spectrometry-based
peptide fingerprinting permitted assignment of individual proteins to A511 structural components. On the basis of the data available for A511 and relatives, we propose that SPO1-like Myoviruses are characterized by (i)
infection of
Gram-positive, low G+C-content
bacteria; (ii) wide
host range within the host
bacterial genus and strictly
virulent lifestyle; (iii) similar morphology, sequence
relatedness and collinearity of the
phage genome organization, and (iv) large
dsDNA genomes featuring non-permuted, terminal redundant repeats of variable size.
