New Species of Kronosvirus Bacteriophages That Infect Caulobacter Strain CBR1

Caulobacter segnis strain CBR1 enhances the germination rate and total biomass of Arabidopsis plants. Since bacteriophages are usually present in the rhizosphere, we isolated three additional bacteriophages, designated TMCBR2, TMCBR3, and W2, that can replicate using CBR1 as the host strain. The genome sizes and morphologies of the new phages were similar to those of the previously isolated Kronos phage, and when we compared the nucleotide sequence of these new phage genomes, we found only minor differences among the four phage genomes. Pairwise sequence comparisons indicated that the phage genomes should be grouped into three separate species within Kronosvirus genus. Interestingly, we found that most of the genomic variation occurred among genes of unknown function within a 10 kb region of the 42 kb genomes with little variation in the remaining 32 kb which contains the genes known to be important for phage propagation.