Document Detail

Porins are required for uptake of phosphates by Mycobacterium smegmatis.
MedLine Citation:
PMID:  17209034     Owner:  NLM     Status:  MEDLINE    
Phosphorus is an essential nutrient, but how phosphates cross the mycobacterial cell wall is unknown. Phosphatase activity in whole cells of Mycobacterium smegmatis was significantly lower than that in lysed cells, indicating that access to the substrate was restricted. The loss of the outer membrane (OM) porin MspA also reduced the phosphatase activity in whole cells compared to that in lysed cells. A similar result was obtained for M. smegmatis that overexpressed endogenous alkaline phosphatase, indicating that PhoA is not a surface protein, contrary to a previous report. The uptake of phosphate by a mutant lacking the porins MspA and MspC was twofold lower than that by wild-type M. smegmatis. Strikingly, the loss of these porins resulted in a severe growth defect of M. smegmatis on low-phosphate plates. We concluded that the OM of M. smegmatis represents a permeability barrier for phosphates and that Msp porins are the only OM channels for the diffusion of phosphate in M. smegmatis. However, phosphate diffusion through Msp pores is rather inefficient as shown by the 10-fold lower permeability of M. smegmatis for phosphate compared to that for glucose. This is likely due to the negative charges in the constriction zone of Msp porins. The phosphatase activity in whole cells of Mycobacterium bovis BCG was significantly less than that in lysed cells, indicating a similar uptake pathway for phosphates in slow-growing mycobacteria. However, porins that could mediate the diffusion of phosphates across the OM of M. bovis BCG and Mycobacterium tuberculosis are unknown.
Frank Wolschendorf; Maysa Mahfoud; Michael Niederweis
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2007-01-05
Journal Detail:
Title:  Journal of bacteriology     Volume:  189     ISSN:  0021-9193     ISO Abbreviation:  J. Bacteriol.     Publication Date:  2007 Mar 
Date Detail:
Created Date:  2007-03-01     Completed Date:  2007-04-03     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2985120R     Medline TA:  J Bacteriol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2435-42     Citation Subset:  IM    
Department of Microbiology, University of Alabama at Birmingham, Mail Box 24, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL 35294, USA.
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MeSH Terms
Alkaline Phosphatase / genetics,  metabolism
Cell Membrane / metabolism
Cell Membrane Permeability
Culture Media
Gene Expression Regulation, Bacterial
Mycobacterium smegmatis / enzymology,  genetics,  growth & development,  metabolism*
Phosphates / metabolism*
Porins / genetics,  metabolism*
Grant Support
Reg. No./Substance:
0/Culture Media; 0/MspC protein, Mycobacterium smegmatis; 0/Phosphates; 0/Porins; 0/mspA protein, Mycobacterium smegmatis; EC Phosphatase

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