The periplasmic, group III catalase of Vibrio fischeri is required for normal symbiotic competence and is induced both by oxidative stress and by approach to stationary phase - PubMed (original) (raw)

The periplasmic, group III catalase of Vibrio fischeri is required for normal symbiotic competence and is induced both by oxidative stress and by approach to stationary phase

K L Visick et al. J Bacteriol. 1998 Apr.

Abstract

The catalase gene, katA, of the sepiolid squid symbiont Vibrio fischeri has been cloned and sequenced. The predicted amino acid sequence of KatA has a high degree of similarity to the recently defined group III catalases, including those found in Haemophilus influenzae, Bacteroides fragilis, and Proteus mirabilis. Upstream of the predicted start codon of katA is a sequence that closely matches the consensus sequence for promoters regulated in Escherichia coli by the alternative sigma factor encoded by rpoS. Further, the level of expression of the cloned katA gene in an E. coli rpoS mutant is much lower than in wild-type E. coli. Catalase activity is induced three- to fourfold both as growing V. fischeri cells approach stationary phase and upon the addition of a small amount of hydrogen peroxide during logarithmic growth. The catalase activity was localized in the periplasm of wild-type V. fischeri cells, where its role could be to detoxify hydrogen peroxide coming from the external environment. No significant catalase activity could be detected in a katA null mutant strain, demonstrating that KatA is the predominately expressed catalase in V. fischeri and indicating that V. fischeri carries only a single catalase gene. The catalase mutant was defective in its ability to competitively colonize the light organs of juvenile squids in coinoculation experiments with the parent strain, suggesting that the catalase enzyme plays an important role in the symbiosis between V. fischeri and its squid host.

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Figures

FIG. 1

FIG. 1

(A) Partial maps of plasmids used in this study. Plasmids pLP2, pKV48, and pKV75 are derivatives of pBluescript KS (Stratagene), a portion of which, including the multiple cloning site, is denoted by the thin line. The V. fischeri catalase gene, katA, is indicated by the black box, and the erythromycin resistance gene, erm, is indicated by the gray box. Transcription of the lacZ gene is in the direction of the arrow. (B) Nucleotide sequence upstream of the V. fischeri katA gene from the _Eco_RI site to the putative ATG start codon. Nucleotides in the putative ribosome binding site upstream of the gene are underlined in bold, and a potential −10 promoter sequence is in boldface. Nucleotides that match the proposed OxyR consensus sequence (41, 42) are in boldface and underlined, while those that match the region upstream of the H. influenzae hktE gene, where an OxyR binding site has been proposed (6), are underlined. The proposed OxyR motifs are displayed above. The putative ATG start site is shown in shadowbox letters.

FIG. 2

FIG. 2

Catalase specific activity during the growth of V. fischeri ES114. The average optical density of the cultures is indicated by open squares; catalase specific activity, reported in units/milligram of protein, is designated by black circles. The data are averages of activity assays performed on extracts of triplicate cultures. The error bars are equal to 1 standard deviation.

FIG. 3

FIG. 3

Colonization of juveniles of the squid E. scolopes by the katA mutant and its parent. Juveniles of E. scolopes were exposed to a 1:1 mixture of the katA mutant and its wild-type parent. The percentage of the katA mutant strain in the population of V. fischeri cells colonizing the light organ was determined for each animal at 17 h postinoculation.

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