title: The growth rate of Mycobacterium smegmatis depends on sufficient porin-mediated influx of nutrients.
abstract: Mycobacteria have a unique outer membrane (OM) that is thicker than any other known biological membrane. Nutrients cross this permeability barrier by diffusion through porins. MspA is the major porin of Mycobacterium smegmatis. In this study we showed that three paralogues of MspA, namely MspB, MspC and MspD are also porins. However, only the mspA and mspC genes were expressed in the wild-type strain. None of the single deletion mutants displayed a significant OM permeability defect except for the mspA mutant. Deletion of the mspA gene caused activation of transcription of mspB and/or mspD in three independent strains by unknown chromosomal mutations. It is concluded that mspB and mspD provide backup porins for M. smegmatis. This also indicated that a minimal porin-mediated OM permeability is essential for survival of M. smegmatis. Electron microscopy in combination with quantitative image analysis of protein gels revealed that the number of pores per cell dropped from 2400 to 800 and 150 for the DeltamspA and DeltamspA DeltamspC mutant (ML10) respectively. The very low number of pores correlated well with the at least 20-fold lower channel activity of detergent extracts of the ML10 strain and its 15- and 75-fold lower permeability to nutrient molecules such as serine and glucose respectively. The amount of Msp porin and the OM permeability of the triple porin mutant lacking mspA, mspC and mspD was not altered. The growth rate of M. smegmatis dropped drastically with its porin-mediated OM permeability in contrast to porin mutants of Escherichia coli. These results show that porin-mediated influx of nutrients is a major determinant of the growth rate of M. smegmatis.
authors.affiliation: Lehrstuhl für Mikrobiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Stephan
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bender
authors.forename: Frank
authors.initials: F
authors.lastname: Wolschendorf
authors.forename: Christian
authors.initials: C
authors.lastname: Hoffmann
authors.forename: Eva
authors.initials: E
authors.lastname: Roth
authors.forename: Claudia
authors.initials: C
authors.lastname: Mailänder
authors.forename: Harald
authors.initials: H
authors.lastname: Engelhardt
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000502:physiology*; D002509:Cephaloridine / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D020102:Mycobacterium smegmatis / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D018272:Porins / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C434272:MspC protein, Mycobacterium smegmatis; D018272:Porins; C121838:mspA protein, Mycobacterium smegmatis; D005947:Glucose; D002509:Cephaloridine