A membrane protein preserves intrabacterial pH in intraphagosomal Mycobacterium tuberculosis

Omar H Vandal, et al. 2008. Nature Medicine. 14, 849-854

Student: Yu-Ping Chang (張鈺苹)                                           Time: 15:00~16:00, Dec. 10, 2008

Commentator: Dr. Lien-I Hor (何漣漪 博士)                        Place: Room 601

Abstract:

Mycobacterium tuberculosis (Mtb), an intracellular pathogen, is a microorganism adapting to acidic environment and can be a long-term resident in macrophage phagosomes.¹ Intracellular Mtb blocks the fusion of phagosome with lysosome to prevent phagosome acidification.² After 10,100 Mtb transposon mutants were screened,³ the authors identified 34 mutants containing 21 genes. Only two mutants remained hypersensitive to pH 4.5 when they replaced Tween with either Tyloxapol or pcit in 7H9 growth medium. These two mutants Rv3671c and Rv2136c were acid sensitive compared with wild-type H37Rv. Rv3671c is predicted to be a serine protease and has an active serine site. While Rv3671c mutant was complemented with wild-type but not mutant S343A, the acid resistance was recovered. By Flag-tagged labeling, the expression of Rv3671c was identified in cell envelope but not in cytosol. By intrabacterial pH (pH_IB) determination, the Rv3671c mutant did not maintain pH_IB and was killed within IFN-g-activated macrophages. In mice infected by inhalation, the Rv3671c mutant but not complemented mutant was impaired for growth in the lung and spleen, suggested that Rv3671c is required for Mtb growth and persistence in vivo. Taken together, Mtb envelope protein Rv3671c is essential for regulating Mtb growth in macrophages to escape from bacterial clearance by acidification of phagosome.

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