S2B, a Temperate Bacteriophage That Infects Caulobacter Crescentus Strain CB15

Abstract

The Caulobacter crescentus strain CB15 has been the basis of numerous studies designed to characterize the biphasic life cycle of this bacterium. Here we describe a newly isolated podovirus, designated S2B, which is capable of integrating into the CB15 chromosome by recombining with the 3'-end of a particular tRNA^-ser gene. In addition, we show that S2B is a representative of a family of closely related prophages that are present in the genomes of characterized strains from several Alphaproteobacteria genera. In contrast, only distantly related bacteriophage genomes are present in the GenBank database. The 42,846 bp S2B genome includes 262 bp terminal repeats, and it contains 62 genes of which 45 code for proteins of unknown function. Proteins with predicted functions include a T7 DNA polymerase, a T3/T7 RNA polymerase, and a T7 helicase/primase suggesting that S2B is part of the Studiervirinae subfamily of the Autographiviridae family.

Fig. 1

An electron micrograph of the S2B phage capsid. The distance between each vertical line at the bottom of the figure is 10 nm

Fig. 2

A phylogenetic tree showing the relationships between the S2B DNA polymerase and six other closely related DNA polymerases