PMID:14645281

Citation	Whistler, CA and Ruby, EG (2003) GacA regulates symbiotic colonization traits of Vibrio fischeri and facilitates a beneficial association with an animal host. J. Bacteriol. 185:7202-12
Abstract	The GacS/GacA two-component system regulates the expression of bacterial traits during host association. Although the importance of GacS/GacA as a regulator of virulence is well established, its role in benign associations is not clear, as mutations in either the gacS or gacA gene have little impact on the success of colonization in nonpathogenic associations studied thus far. Using as a model the symbiotic association of the bioluminescent marine bacterium Vibrio fischeri with its animal host, the Hawaiian bobtail squid, Euprymna scolopes, we investigated the role of GacA in this beneficial animal-microbe interaction. When grown in culture, gacA mutants were defective in several traits important for symbiosis, including luminescence, growth in defined media, growth yield, siderophore activity, and motility. However, gacA mutants were not deficient in production of acylated homoserine lactone signals or catalase activity. The ability of the gacA mutants to initiate squid colonization was impaired but not abolished, and they reached lower-than-wild-type population densities within the host light organ. In contrast to their dark phenotype in culture, gacA mutants that reached population densities above the luminescence detection limit had normal levels of luminescence per bacterial cell in squid light organs, indicating that GacA is not required for light production within the host. The gacA mutants were impaired at competitive colonization and could only successfully cocolonize squid light organs when present in the seawater at higher inoculum densities than wild-type bacteria. Although severely impaired during colonization initiation, gacA mutants were not displaced by the wild-type strain in light organs that were colonized with both strains. This study establishes the role of GacA as a regulator of a beneficial animal-microbe association and indicates that GacA regulates utilization of growth substrates as well as other colonization traits.
Links	PubMed PMC296250
Keywords	4-Butyrolactone/analogs & derivatives; 4-Butyrolactone/metabolism; Aldehydes/metabolism; Amino Acids/metabolism; Animals; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Cloning, Molecular; Decapodiformes/microbiology; Genetic Complementation Test; Luminescent Measurements; Microbiological Techniques; Mutagenesis; Symbiosis; Vibrio/genetics; Vibrio/growth & development; Vibrio/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ALIFS:Q6U738		GO:0035556: intracellular signal transduction	ECO:0000315:		P		Fig. 3 demonstrate that one of the Vibrio fischeri GacA global regulator functions is in luminescence. Mutants are defective in luminescence by measuring LU/OD600.	complete CACAO 8607
ALIFS:Q6U738	involved_in	GO:0035556: intracellular signal transduction	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Seeded From UniProt	complete

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