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Inactivation of the Spirochete recA Gene Results in a Mutant with Low Viability and Irregular Nucleoid Morphology. Ange-Patricia Tchamedeu Kameni, 2002.Recently, we have shown the first evidence for allelic exchange in Leptospira spp . By using the same methodology, the cloned recA of Leptospira biflexa was interrupted by a kanamycin resistance cassette, and the mutated allele was then introduced into the L . biflexa chromosome by homologous recombination . The recA double-crossover mutant showed poor growth in liquid media and was considerably more sensitive to DNA-damaging agents such as mitomycin C and UV light than the wild-type strain . The efficiency of plating of the recA mutant was about 10% of that of the parent strain . In addition, microscopic observation of the L . biflexa recA mutant showed cells that are more elongated than those of the wild-type strain . Fluorescent microscopy of stained cells of the L . biflexa wild-type strain revealed that chromosomal DNA is distributed throughout most of the length of the cell . In contrast, the recA mutant showed aberrant nucleoid morphologies, i.e., DNA is condensed at the midcell . Our data indicate that L . biflexa RecA plays a major role in ensuring cell viability via mechanisms such as DNA repair and, indirectly, active chromosome partitioning . Complete Genomic Sequence of SfV, a Serotype-Converting Temperate Bacteriophage of Shigella flexneri. Gwen E. Allison, 2002.Bacteriophage SfV is a temperate serotype-converting phage of Shigella flexneri. SfV encodes the factors involved in type V O-antigen modification, and the serotype conversion and integration-excision modules of the phage have been isolated and characterized . We now report on the complete sequence of the SfV genome (37,074 bp) . A total of 53 open reading frames were predicted from the nucleotide sequence, and analysis of the corresponding proteins was used to construct a functional map . The general organization of the genes in the SfV genome is similar to that of bacteriophage  , and numerous features of the sequence are described . The superinfection immunity system of SfV includes a lambda-like repression system and a P4-like transcription termination mechanism . Sequence analysis also suggests that SfV encodes multiple DNA methylases, and experiments confirmed that orf-41 encodes a Dam methylase . Studies conducted to determine if the phage-encoded methylase confers host DNA methylation showed that the two S. flexneri strains analyzed encode their own Dam methylase . Restriction mapping and sequence analysis revealed that the phage genome has cos sites at the termini . The tail assembly and structural genes of SfV show homology to those of phage Mu and Mu-like prophages in the genome of Escherichia coli O157:H7 and Haemophilus influenzae . Significant homology (30% of the genome in total) between sections of the early, regulatory, and structural regions of the SfV genome and the e14 and KpLE1 prophages in the E. coli K-12 genome were noted, suggesting that these three phages have common evolutionary origins .
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