CONSTRUCTION AND SYMBIOTIC COMPETENCE OF A LUXA-DELETION MUTANT OF VIBRIO-FISCHERI

Bioluminescence by the squid Euprymna scolopes requires colonization o f its light organ by the symbiotic luminous bacterium Vibrio fischeri. Investigation of the genetic determinants underlying bacterial symbio tic competence in this system has necessitated the continuing establis hment and application of molecular genetic techniques in V. fischeri. We developed a procedure for the introduction of plasmid DNA into V. f ischeri by electroporation, and isolated a mutant strain that overcame the apparent restriction barrier between V. fischeri and Escherichia coli. Using the technique of electroporation in combination with that of gene replacement, we constructed a non-luminous strain of V. fische ri (Delta luxA::erm). In addition, we used the transducing phage rp-l for the first time to transfer a chromosomal antibiotic resistance mar ker to another strain of V. fischeri. The luxA mutant was able to colo nize E. scolopes as quickly and to the same extent as wild type. This result suggested that, at least during the initial stages of colonizat ion, luminescence per se is not an essential factor for the symbiotic infection.