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Journal of Bacteriology, March 2009, p. 1827-1837, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01553-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cystathionine {gamma}-Lyase Is a Component of Cystine-Mediated Oxidative Defense in Lactobacillus reuteri BR11{triangledown}

Raquel Lo,1 Mark S. Turner,2 Daniel G. Barry,1 Revathy Sreekumar,2 Terence P. Walsh,1 and Philip M. Giffard3,1*

Infectious Diseases Program, Cells and Tissues Domain, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia,1 School of Land, Crop and Food Sciences, University of Queensland, Brisbane, Queensland, Australia,2 Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia3

Received 1 November 2008/ Accepted 23 December 2008

Lactobacillus reuteri BR11 possesses a novel mechanism of oxidative defense involving an abundant cystine ABC transporter encoded by the cyuABC gene cluster. Large amounts of thiols, including H2S, are secreted upon cystine uptake by the CyuC transporter. A cystathionine {gamma}-lyase (cgl) gene is cotranscribed with the cyu genes in several L. reuteri strains and was hypothesized to participate in cystine-mediated oxidative defense by producing reducing equivalents. This hypothesis was tested with L. reuteri BR11 by constructing a cgl mutant (PNG901) and comparing it to a similarly constructed cyuC mutant (PNG902). Although Cgl was required for H2S production from cystine, it was not crucial for oxidative defense in de Mann-Rogosa-Sharpe medium, in contrast to CyuC, whose inactivation resulted in lag-phase arrest in aerated cultures. The importance of Cgl in oxidative defense was seen only in the presence of hemin, which poses severe oxidative stress. The growth defects in aerated cultures of both mutants were alleviated by supplementation with cysteine (and cystine in the cgl mutant) but not methionine, with the cyuC mutant showing a much higher concentration requirement. We conclude that L. reuteri BR11 requires a high concentration of exogenous cysteine/cystine to grow optimally under aerobic conditions. This requirement is fulfilled by the abundant CyuC transporter, which has probably arisen due to the broad substrate specificity of Cgl, resulting in a futile pathway which degrades cystine taken up by the CyuC transporter to H2S. Cgl plays a secondary role in oxidative defense by its well-documented function of cysteine biosynthesis.

* Corresponding author. Mailing address: Menzies School of Health Research, Royal Darwin Hospital Campus, Casuarina, NT 0810, Australia. Phone: 61 8 8944 8040. Fax: 61 8 8927 5187. E-mail: phil.giffard{at}menzies.edu.au

{triangledown} Published ahead of print on 5 January 2009.

Journal of Bacteriology, March 2009, p. 1827-1837, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01553-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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