Affiliation:
1. Graduate School of Life Sciences, Tohoku University, Sendai, Japan
2. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
Abstract
ABSTRACT
The outer membrane of heterotrophic Gram-negative bacteria plays the role of a selective permeability barrier that prevents the influx of toxic compounds while allowing the nonspecific passage of small hydrophilic nutrients through porin channels. Compared with heterotrophic Gram-negative bacteria, the outer membrane properties of cyanobacteria, which are Gram-negative photoautotrophs, are not clearly understood. In this study, using small carbohydrates, amino acids, and inorganic ions as permeation probes, we determined the outer membrane permeability of
Synechocystis
sp. strain PCC 6803 in intact cells and in proteoliposomes reconstituted with outer membrane proteins. The permeability of this cyanobacterium was >20-fold lower than that of
Escherichia coli
. The predominant outer membrane proteins Slr1841, Slr1908, and Slr0042 were not permeable to organic nutrients and allowed only the passage of inorganic ions. Only the less abundant outer membrane protein Slr1270, a homolog of the
E. coli
export channel TolC, was permeable to organic solutes. The activity of Slr1270 as a channel was verified in a recombinant Slr1270-producing
E. coli
outer membrane. The lack of putative porins and the low outer membrane permeability appear to suit the cyanobacterial autotrophic lifestyle; the highly impermeable outer membrane would be advantageous to cellular survival by protecting the cell from toxic compounds, especially when the cellular physiology is not dependent on the uptake of organic nutrients.
IMPORTANCE
Because the outer membrane of Gram-negative bacteria affects the flux rates for various substances into and out of the cell, its permeability is closely associated with cellular physiology. The outer membrane properties of cyanobacteria, which are photoautotrophic Gram-negative bacteria, are not clearly understood. Here, we examined the outer membrane of
Synechocystis
sp. strain PCC 6803. We revealed that it is relatively permeable to inorganic ions but is markedly less permeable to organic nutrients, with >20-fold lower permeability than the outer membrane of
Escherichia coli
. Such permeability appears to fit the cyanobacterial lifestyle, in which the diffusion pathway for inorganic solutes may suffice to sustain the autotrophic physiology, illustrating a link between outer membrane permeability and the cellular lifestyle.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
42 articles.
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