Novel effects of a transposon insertion in the Vibrio fischeri glnD gene: defects in iron uptake and symbiotic persistence in addition to nitrogen utilization

Vibrio fischeri is the sole species colonizing the light-emitting organ of the Hawaiian squid, Euprymna scolopes. Upon entering the nascent light orga n of a newly hatched juvenile squid, the bacteria undergo morphological and physiological changes that include the loss of flagellation and the induct ion of bioluminescence. These and other events reveal a pattern of genetic regulation that is a response to the colonization of host tissue. In this s tudy, we isolated and characterized a glnD::mTn5Cm mutant of V. fischeri. I n addition to the predicted defects in the efficiency of nitrogen utilizati on, this glnD mutant had an unexpected reduction in the ability to produce siderophore and grow under iron-limiting conditions. Although the glnD muta nt could colonize juvenile squid normally over the first 24 h, it was subse quently unable to persist in the light organ to the usual extent. This pers istence phenotype was more severe if the mutant was pregrown under iron-lim iting conditions before inoculation, but could be ameliorated by the presen ce of excess iron. These results indicate that the ability to respond to ir on limitation may be an important requirement in the developing symbiosis. Supplying the glnD gene in trans restored normal efficiency of nitrogen use , iron sequestration and colonization phenotypes to the glnD::mTn5Cm mutant ; thus, there appears to be a genetic and/or metabolic linkage between nitr ogen sensing, siderophore synthesis and symbiosis competence in V. fischeri that involves the glnD gene.