Transcriptional activity of the host-interaction locus and a putative pilin gene of Bdellovibrio bacteriovorus in the predatory life cycle

Bdellovibrio bacteriovorus is a predatory bacterium that grows and replicates within the periplasm of a large variety of Gram-negative bacteria. So far, the host-interaction locus (hit locus) is the only genetic locus that is implicated in the obligate predatory lifestyle. Sequence analysis revealed that upstream of the hit locus, the genomic regions of the two obligate predatory B. bacteriovorus-type strains HD100 and HD114 encode genes for pilus formation. As pili might be involved in the invasion process, the transcriptional activity of the hit locus and of a putative pilin gene (flp1) of the pilus cluster were studied in synchronized cultures of B. bacteriovorus with Escherichia coli K-12 as prey bacteria. Stages of the life cycle were monitored with scanning electronic microscopy and transcriptional analyses were performed by quantitative reverse transcription polymerase chain reaction. Our study revealed an increased expression level of the putative hit and flp1 genes in the attack phase of B. bacteriovorus, whereas the transcriptional activity significantly decreased during the intracellular replication phase.