Revival of heat-damagedEscherichia coli

Résumé Une recherche a été faite sur quelques facteurs ayant une influence sur le retour à la vied'Escherichia coli endommagé par la chaleur. On a obtenu plus de survivants par la méthode «pour-plate» que par la méthode «surface-viable». C'est l'extrait du ferment Difco, et non celui de l'Oxoid, qui a stimulé la guérison des bactéries chauffées. Dans un milieu synthétique, il y a eu peu de survivants.     

Protein kinase activity in Escherichia coli]

When growing E. coli in a minimal medium, at least four proteins from the soluble fraction and one ribosome-associated protein are found phosphorylated at the level of their threonine and serine residues.     

Evolution of virulence factors in Shiga-toxin-producing Escherichia coli

The major demonstrated or putative virulence factors of Shiga-toxin-producing Escherichia coli (STEC) are the Shiga toxins, products of the locus of enterocyte effacement, and products encoded by the EHEC-hemolysin plasmid. Molecular analysis shows that STEC acquired the majority of these virulence factors by horizontal transfer of genetic material. In the case of Shiga toxins, the phages encoding them are probably responsible for this transfer. For the locus of enterocyte effacement, however, it is not clear how often this transfer took place and which parts of the locus were involved in this transfer. The large EHEC-hemolysin plasmid is clearly a mosaic structure, which arose from multiple recombination events with foreign DNA. Two lineages of this plasmid can be distinguished, one of which is associated with chromosomally encoded virulence factors. Despite the wealth of information available, further comparative studies are needed to decipher definitively the evolution of virulence in STEC.     

Proteases and protein degradation in Escherichia coli.

In E. coli, protein degradation plays important roles in regulating the levels of specific proteins and in eliminating damaged or abnormal proteins. E. coli possess a very large number of proteolytic enzymes distributed in the cytoplasm, the inner membrane, and the periplasm, but, with few exceptions, the physiological functions of these proteases are not known. More than 90% of the protein degradation occurring in the cytoplasm is energy-dependent, but the activities of most E. coli proteases in vitro are not energy-dependent. Two ATP-dependent proteases, Lon and Clp, are responsible for 70-80% of the energy-dependent degradation of proteins in vivo. In vitro studies with Lon and Clp indicate that both proteases directly interact with substrates for degradation. ATP functions as an allosteric effector promoting an active conformation of the proteases, and ATP hydrolysis is required for rapid catalytic turnover of peptide bond cleavage in proteins. Lon and Clp show virtually no homology at the amino acid level, and thus it appears that at least two families of ATP-dependent proteases have evolved independently.     

The structure and function of Escherichia coli penicillin-binding protein 3

Escherichia coli penicillin-binding protein PBP3 is a key element in cell septation. It is presumed to catalyse a transpeptidation reaction during biosynthesis of the septum peptidoglycan but, in vitro, its enzymatic activity has only been demonstrated with thiolester analogues of the natural peptide substrate. It has no detectable transglycosylase activity with lipid II as substrate. This tripartite protein is constructed of an N-terminal membrane anchor-containing module that is essential for cell septation, a non-penicillin-binding (n-PB) module of unknown function and a C-terminal penicillin-binding (PB) module exhibiting all the characteristic motifs of penicilloyl serine transferases. The n-PB module, which is required for the folding and stability of the PB module, may provide recognition sites for other cell division proteins. Initiation of septum formation is not PBP3-dependent but rests on the appearance of the FtsZ ring, and is thus penicillin-insensitive. The control of PBP3 activity during the cell cycle is briefly discussed.