Synthetic Mimic of Antimicrobial Peptide with Nonmembrane-Disrupting Antibacterial Properties

Proteolysis in dairy lactic acid bacteria has been studied in great detail by genetic, biochemical and ultrastructural methods. From these studies the picture emerges that the proteolytic systems of lactococci and lactobacilli are remarkably similar in their components and mode of action. The proteolytic system consists of an extracellularly located serine-proteinase, transport systems specific for di-tripeptides and oligopeptides (> 3 residues), and a multitude of intracellular peptidases. This review describes the properties and regulation of individual components as well as studies that have led to identification of their cellular localization. Targeted mutational techniques developed in recent years have made it possible to investigate the role of individual and combinations of enzymes in vivo. Based on these results as well as in vitro studies of the enzymes and transporters, a model for the proteolytic pathway is proposed. The main features are: (i) proteinases have a broad specificity and are capable of releasing a large number of different oligopeptides, of which a large fraction falls in the range of 4 to 8 amino acid residues; (ii) oligopeptide transport is the main route for nitrogen entry into the cell; (iii) all peptidases are located intracellularly and concerted action of peptidases is required for complete degradation of accumulated peptides.

Characterization of the Divergent sacBK and sacAR Operons, Involved in Sucrose Utilization by Lactococcus lactis

The divergently transcribed sacBK and sacAR operons, which are involved in the utilization of sucrose by Lactococcus lactis NZ9800, were examined by transcriptional and gene inactivation studies. Northern analyses of RNA isolated from cells grown at the expense of different carbon sources revealed three sucrose-inducible transcripts: one of 3.2 kb containing sacB and sacK, a second of 3.4 kb containing sacA and sacR, and a third of 1.8 kb containing only sacR. The inactivation of the sacR gene by replacement recombination resulted in the constitutive transcription of the sacBK and sacAR operons in the presence of different carbon sources, indicating that SacR acts as a repressor of transcription

Nitrogen control in Pseudomonas aeruginosa: mutants affected in the synthesis of glutamine synthetase, urease, and NADP-dependent glutamate dehydrogenase.

Mutants were isolated from Pseudomonas aeruginosa that were impaired in the utilization of a number of nitrogen sources. In contrast to the wild-type strain, these mutants appeared to be unable to derepress the formation of glutamine synthetase and urease under nitrogen-limited growth conditions, whereas NADP-dependent glutamate dehydrogenase became derepressed. This GlnR- phenotype appeared to be caused by a mutation located in the early region of the P. aeruginosa PAO chromosomal map, close to hisIV59. Partial suppression of the GlnR- phenotype due to a mutation located close to hisII4 was observed. These revertants were different from both the wild-type strain and the GlnR- mutant with respect to the regulation of the synthesis of glutamine synthetase, urease, and NADP-dependent glutamate dehydrogenase (GlnRc phenotype). Also the regulation of glutamine synthetase activity by adenylylation/deadenylylation was altered in the revertants. The results suggest the presence of a regulatory gene that plays a role in the regulation of enzyme formation in response to the availability of ammonia