This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Nawawi, R. A.
Right arrow Articles by Barnes, A. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Nawawi, R. A.
Right arrow Articles by Barnes, A. C.
Agricola
Right arrow Articles by Nawawi, R. A.
Right arrow Articles by Barnes, A. C.

 Previous Article  |  Next Article 

Applied and Environmental Microbiology, May 2009, p. 2908-2919, Vol. 75, No. 9
0099-2240/09/$08.00+0     doi:10.1128/AEM.02147-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Host-Directed Evolution of a Novel Lactate Oxidase in Streptococcus iniae Isolates from Barramundi (Lates calcarifer){triangledown}

Roslina A. Nawawi, Justice C. F. Baiano, E. Charlotte E. Kvennefors, and Andrew C. Barnes*

The University of Queensland, Aquatic Animal Health Laboratory, Centre for Marine Studies, Brisbane, Queensland 4072, Australia

Received 17 September 2008/ Accepted 2 March 2009

In Streptococcus iniae, lactate metabolism is dependent upon two proteins, lactate permease that mediates uptake and lactate oxidase, a flavin mononucleotide-dependent enzyme that catalyzes oxidation of {alpha}-hydroxyacids. A novel variant of the lactate oxidase gene, lctO, in Australian isolates of S. iniae from diseased barramundi was found during a diagnostic screen using LOX-1 and LOX-2 primers, yielding amplicons of 920 bp instead of the expected 869 bp. Sequencing of the novel gene variant (type 2) revealed a 51-nucleotide insertion in lctO, resulting in a 17-amino-acid repeat in the gene product, and three-dimensional modeling indicated formation of an extra loop in the monomeric protein structure. The activities of the lactate oxidase enzyme variants expressed in Escherichia coli were examined, indicating that the higher-molecular-weight type 2 enzyme exhibited higher activity. Growth rates of S. iniae expressing the novel type 2 enzyme were not reduced at lactate concentrations of 0.3% and 0.5%, whereas a strain expressing the type 1 enzyme exhibited reduced growth rates at these lactate concentrations. During a retrospective screen of 105 isolates of S. iniae from Australia, the United States, Canada, Israel, Réunion Island, and Thailand, the type 2 variant arose only in isolates from a single marine farm with unusually high tidal flow in the Northern Territory, Australia. Elevated plasma lactate levels in the fish, resulting from the effort of swimming in tidal flows of up to 3 knots, may exert sufficient selective pressure to maintain the novel, high-molecular-weight enzyme variant.

* Corresponding author. Mailing address: Aquatic Animal Health Laboratory, Centre for Marine Studies, The University of Queensland, Brisbane, Queensland 4072, Australia. Phone: 61 7 3346 9416. Fax: 61 7 3365 4755. E-mail: a.barnes{at}uq.edu.au

{triangledown} Published ahead of print on 6 March 2009.

Applied and Environmental Microbiology, May 2009, p. 2908-2919, Vol. 75, No. 9
0099-2240/09/$08.00+0     doi:10.1128/AEM.02147-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»