M A de Pedro

Effect of D-amino acids on Escherichia coli strains with impaired penicillin-binding proteins

Escherichia coli cells growing in the presence of some D-amino acids incorporate D-amino acid into the peptidoglycan layer of the cell wall by a mechanism most likely independent of the normal biosynthetic pathway. Analysis of the sensitivity of mutant strains with impaired penicillin-binding proteins (PBP) to D-amino acids indicated that ponB and DD-endopeptidase/DD-carboxypeptidase-I-defective strains are hypersensitive to D-amino acids. D-tryptophan containing peptidoglycan was found to be more susceptible to the action of lytic transglycosilases than native material, which could explain in part the harmful effects of D-amino acids. ponB strains carrying additional mutations suppressing hypersensitivity to D-amino acids have been obtained and the results of their initial characterization are reported.

Application of a charge/size two-dimensional gel electrophoresis system to the analysis of the penicillin-binding proteins of Escherichia coli

nor received Penlcdlm-bmdmg protein NEPHGE SDS-PAGE (E. coli)

Phenotypic, Biochemical, and Structural Analysis of “S-layer” Mutants from Thermus thermophilus HB8

S-layers are crystalline proteinaceous structures that surround a high number of wild type bacteria, being specially frequent among thermophiles (Sleytr and Messner, 1983). Their role and biochemical properties have been discussed extensively by a number of authors (Sara and Sleytr, 1977; Baumeister and Engelhardt, 1987; Hovmoller et al., 1988), and, from these analyses, it could be concluded that there exist, at least, two well differentiated classes of S-layers, depending on the degree of interaction with the cell envelope. The first group is represented by bona fide Gram positive organisms, such as Bacillus brevis, B. stearothermophilus etc., in which the crystalline structure can be easily extracted from the envelope (Sleytr and Messner, 1983). In these bacteria, defective mutants in the S-layer synthesis with no apparent phenotypic defects can be obtained by spontaneous mutations (Ishiguro et al., 1981). Furthermore, it has been suggested that the presence of the S-layer is a counter-selected character under laboratory conditions for this group of organisms (Baumeister and Engelhardt, 1987).