A PLASMID VECTOR WITH A SELECTABLE MARKER FOR HALOPHILIC ARCHAEBACTERIA

A mutant resistant to the gyrase inhibitor novobiocin was selected from a halophilic archaebacterium belonging to the genus Haloferax. Chromosomal DNA from this mutant was able to transform wild-type cells to novobiocin resistance, and these transformants formed visible colonies in 3 to 4 days on selective plates. The resistance gene was isolated on a 6.7-kilobase DNA Kpn1 fragment, which was inserted into a cryptic multicopy plasmid (pHK2) derived from the same host strain. The recombinant plasmid transformed wild-type cells at a high efficiency (>106/μg), was stably maintained, and could readily be reisolated from transformants. It could also transform Halobacterium volcanii and appears to be a useful system for genetic analysis in halophilic archaebacteria.