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Haem utilization in Vibrio cholerae involves multiple TonB-dependent haem receptors.
1Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712-1095, USA.
Molecular Microbiology
|November 28, 2001
Summary
Vibrio cholerae utilizes multiple outer membrane receptors, HutA, HutR, and HasR, for heme iron uptake. A triple mutant lacking all three receptors cannot utilize heme, highlighting their importance for iron acquisition.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Vibrio cholerae requires iron for growth and possesses multiple iron uptake systems.
- Heme is a significant iron source, and its uptake is mediated by outer membrane receptors.
- TonB-dependent transporters are crucial for nutrient uptake across the outer membrane in Gram-negative bacteria.
Purpose of the Study:
- To identify and characterize additional heme uptake systems in Vibrio cholerae beyond the known HutA receptor.
- To investigate the roles of HutR and HasR in heme and hemoglobin utilization.
- To determine the TonB dependency of these heme uptake pathways.
Main Methods:
- Construction and analysis of single, double, and triple mutants for heme uptake.
- Membrane fractionation to confirm receptor localization.
- Gene expression analysis to study regulation of hutR.
- Competition assays in a mouse model of infection.
- Testing utilization of different iron sources like heme and hemoglobin.
Main Results:
- Vibrio cholerae encodes three TonB-dependent heme receptors: HutA, HutR, and HasR.
- HutR is an outer membrane protein, homologous to other heme receptors, and its expression is iron-regulated.
- A triple mutant lacking HutA, HutR, and HasR is unable to utilize heme as an iron source.
- HutA and HutR utilize TonB1 or TonB2, with TonB1 being more efficient for HutA.
- HasR-mediated heme uptake is dependent on TonB2.
- HutA and TonB1 are essential for efficient hemoglobin utilization.
- The triple mutant showed no growth defect in vivo, suggesting alternative iron sources.
Conclusions:
- Vibrio cholerae employs a redundant system of three outer membrane receptors for heme iron acquisition.
- Differential TonB utilization by these receptors provides flexibility in iron uptake.
- Despite the importance of heme uptake in vitro, other iron sources are likely critical during infection.
- Heme from environmental sources like marine invertebrates may contribute to Vibrio cholerae iron acquisition.