,
Nadine Fornelos,
and
Jacques Mahillon*
Université Catholique de Louvain, Louvain-la-Neuve, Belgium
Received 5 October 2004/ Accepted 8 December 2004
One of the most notable characteristics of Tectiviridae resides in their double-layer coats: the double-stranded DNA is located within a flexible lipoprotein vesicle covered by a rigid protein capsid. Despite their apparent rarity, tectiviruses have an extremely wide distribution compared to other phage groups. Members of this family have been found to infect gram-negative (PRD1 and relatives) as well as gram-positive (Bam35, GIL01, AP50, and
NS11) hosts. Several reports have shown that tectiviruses infecting gram-negative bacteria are closely related, whereas no information is currently available on the genetic relationship among those infecting gram-positive bacteria. The present study reports the sequence of GIL16, a new isolate originating from Bacillus thuringiensis, and a genetic comparison of this isolate with the tectiviral bacteriophages Bam35 and GIL01, which originated from B. thuringiensis serovars Alesti and Israelensis, respectively. In contrast to PRD1 and its relatives, these are temperate bacteriophages existing as autonomous linear prophages within the host cell. Mutations in a particular motif in both the GIL01 and GIL16 phages are also shown to correlate with a switch to the lytic cycle. Interestingly, both bacterial viruses displayed narrow, yet slightly different, host spectrums. We also explore the hypothesis that pBClin15, a linear plasmid hosted by the Bacillus cereus reference strain ATCC 14579, is also a prophage. Sequencing of its inverted repeats at both extremities and a comparison with GIL01 and GIL16 emphasize its relationship to the Tectiviridae.
C.V. and N.F. contributed equally to this work.
Present address: Center for Molecular Genetics and Division of Biological Sciences, University of CaliforniaSan Diego, La Jolla, CA 92093-0322.
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