Construction of a packaged strain XL-pⅢ and preparation of defective helper phage / 解放军医学杂志

ABSTRACT

Objective To construct a packaged bacteria strain and, with it, to prepare gene III-defective helper phage. Methods Whole gene III and chloramphenicol-resistant gene were amplified and joined to form a fragment flanking 36bp homologous sequence of hisBCD using overlapping extending PCR, and it was then integrated into chromosome of E. coli XL1-Blue to replace the hisBCD gene using Red recombination system. The recombinant strain was identified with chloramphenicol-resistant screening, PCR and histidine-phenotype analysis, and named as XL-pⅢ. The gene III-deleted genome of phage was constructed with PCR and transfected into the recombinant strain XL-pⅢ to prepare the defective helper phage. It was quantified by infecting E. coli XL1-Blue and formed colonies were counted in kanamycin plate. Results The recombinant strain could grow in chloramphenicol-resistant plate, but couldn't grow in M9 medium without histidine, implying that it had lost its histidine phenotype. The aimed gene fragment could be amplified as designed. The constructed recombinant was named as XL-pⅢ. The prepared defective helper phage could infect E. coli XL1-Blue only once and the CFU was 3.7?108. Conclusions The packaged strain XL-pⅢ is successfully constructed and used to prepare the gene III-deleted helper phage. It is expected to be used in SIP system.