ABSTRACTCampylobacter jejuni, the leading bacterial cause of human gastroenteritis in the United States, displays significant strain diversity due to horizontal gene transfer. Conjugation is an important horizontal gene transfer mechanism contributing to the evolution of bacterial pathogenesis and antimicrobial resistance. It has been observed that heat shock could increase transformation efficiency in some bacteria. In this study, the effect of heat shock onC. jejuniconjugation efficiency and the underlying mechanisms were examined. With a modifiedEscherichia colidonor strain, differentC. jejunirecipient strains displayed significant variation in conjugation efficiency ranging from 6.2 × 10−8to 6.0 × 10−3CFU per recipient cell. Despite reduced viability, heat shock of standardC. jejuniNCTC 11168 and 81-176 strains (e.g., 48 to 54°C for 30 to 60 min) could dramatically enhanceC. jejuniconjugation efficiency up to 1,000-fold. The phenotype of the heat shock-enhanced conjugation inC. jejunirecipient cells could be sustained for at least 9 h. Filtered supernatant from the heat shock-treatedC. jejunicells could not enhance conjugation efficiency, which suggests that the enhanced conjugation efficiency is independent of secreted substances. Mutagenesis analysis indicated that the clustered regularly interspaced short palindromic repeats system and the selected restriction-modification systems (Cj0030/Cj0031, Cj0139/Cj0140, Cj0690c, and HsdR) were dispensable for heat shock-enhanced conjugation inC. jejuni. Taking all results together, this study demonstrated a heat shock-enhanced conjugation efficiency in standardC. jejunistrains, leading to an optimized conjugation protocol for molecular manipulation of this organism. The findings from this study also represent a significant step toward elucidation of the molecular mechanism of conjugative gene transfer inC. jejuni.
Heat Shock-Enhanced Conjugation Efficiency in Standard Campylobacter jejuni Strains
