Structure of the cell envelope of corynebacteria: importance of the non-covalently bound lipids in the formation of the cell wall permeability barrier and fracture plane

Abstract

With the recent success of the heterologous expression of mycobacterial antigens in corynebacteria, in addition to the importance of these bacteria in biotechnology and medicine, a better understanding of the structure of their cell envelopes was needed. A combination of molecular compositional analysis, ultrastructural appearance and freeze-etch electron microscopy study was used to arrive at a chemical model, unique to corynebacteria but consistent with their phylogenetic relatedness to mycobacteria and other members of the distinctive suprageneric actinomycete taxon. Transmission electron microscopy and chemical analyses showed that the cell envelopes of the representative strains of corynebacteria examined consisted of (i) an outer layer composed of polysaccharides (primarily a high-molecular-mass glucan and arabinomannans), proteins, which include the mycoloyltransferase PS1, and lipids ; (ii) a cell wall glycan core of peptidoglycan-arabinogalactan which may contain other sugar residues and was usually esterified by corynomycolic acids ; and (iii) a typical plasma membrane bilayer. Freeze-etch electron microscopy showed that most corynomycolate-containing strains exhibited a main fracture plane in their cell wall and contained low-molecular-mass porins, while the fracture occurred within the plasma membrane of strains devoid of both corynomycolate and pore-forming proteins. Importantly, in most strains, the amount of cell wall-linked corynomycolates was not sufficient to cover the bacterial surface ; interestingly, the occurrence of a cell wall fracture plane correlated with the amount of non-covalently bound lipids of the strains. Furthermore, these lipids were shown to spontaneously form liposomes, indicating that they may participate in a bilayer structure. Altogether, the data suggested that the cell wall permeability barrier in corynebacteria involved both covalently linked corynomycolates and non-covalently bound lipids of their cell envelopes.

Genetic dissection of trehalose biosynthesis in Corynebacterium glutamicum: inactivation of trehalose production leads to impaired growth and an altered cell wall lipid composition

“…Trehalose is found in C. glutamicum cells not only in its free form but also as trehalose mono-(TMCM) and di-(TDCM) corynomycolates, which are the dominant components in the non-covalently bound corynomycolatecontaining lipid fraction of the outer cell wall permeability barrier (Puech et al, 2000(Puech et al, , 2001. Our results show that the inability of C. glutamicum to synthesize trehalose has a significant influence on the composition of its cell wall lipid fraction.…”

“…outer hydrophobic barrier of corynebacterial cells represents a lipid bilayer composed of both covalently cell walllinked mycolates and non-covalently bound glycolipids (Puech et al, 2001). Two trehalose-containing corynomycolic acid esters, i.e.…”

Ammonium Toxicity in Bacteria

“…Evidence for rapid flux of NH 3 across biomembranes was already obtained about 100 years ago (for review, see [18,20]), and high NH 3 diffusion rates were determined in different bacteria, e.g., in Bacillus firmus, Rhodobacter spheroides, and Synechococcus R-2 [26,27]. C. glutamicum has, compared to these already investigated species, a more complex cell wall structure with a mycolic-acid layer functioning as an additional permeability barrier [25]. The concentration of ammonium inside the C. glutamicum cytoplasm was determined.…”

Fluorescent Phospholipid Analogs as Microscopic Probes for Detection of the Mycolic Acid-Containing Layer inCorynebacterium glutamicum: Detecting Alterations in the Mycolic Acid-Containing Layer Following Ethambutol Treatment

“…Mycolate-layer formation, which occurs on existing arabinogalactan residues connected to peptidoglycan-containing cell wall structures, 29,30) cannot occur in the absence of the peptidoglycan layer. According to the electron microscopy studies of Puech et al 29) on C. glutamicum cell surface structures, cytoplasmic membrane first forms with the peptidoglycan layer, and this is followed by formation of the mycolate layer. Based on these requirements, we assumed that exterior parts of the cell surface form after interior parts.…”