We report that the cold shock protein CspA of Staphylococcus aureus is required for maximal production of pigment. Results from transcriptional studies revealed that loss of CspA resulted in decreased expression of genes needed for the biosynthesis of 4,4-diaponeurosporene and the alternative sigma factor SigB.

A Tn551 insertional library of Staphylococcus aureus strain ISP479 was challenged with an antimicrobial peptide (CG 117-136) derived from human neutrophil cathepsin G (CG). After repeated selection and screening of surviving colonies, a mutant was identified that expressed increased resistance to CG 117-136. Southern hybridization analysis revealed that the Tn551 insert in this mutant (SK1) was carried on a 10.6-kb EcoRI chromosomal DNA fragment. Subsequent physical mapping of this Tn551 insert revealed that it was positioned between a putative promoter sequence and the translational start codon of the cspA gene, which encodes a protein (CspA) highly similar to the major cold shock proteins CspA and CspB of Escherichia coli and Bacillus subtilis, respectively. This Tn551 insertion as well as a separate deletion-insertion mutation in cspA decreased the capacity of S. aureus to respond to the stress of cold shock and increased resistance to CG 117-136. The results indicate for the first time that a physiologic link exists between bacterial susceptibility to an antimicrobial peptide and a stress response system.

Neutrophils contain several cationic antimicrobial proteins or peptides (CAPs) that exert antibiotic-like action against bacteria. These host-derived antibiotics kill susceptible bacteria by oxygen-independent mechanisms. Considerable interest in their activity has been generated in recent years due not only to their likely important role in innate host defense against infection, but also their possible use as therapeutic agents in treating infections caused by antibiotic-resistant pathogens. We have studied the antibacterial properties of human lysosomal cathepsin G (cat G). This highly cationic serine protease contains at least three antibacterial regions that by themselves can exert antibacterial action against Gram-negative bacteria, such as Pseudomonas aeruginosa. Only one of these peptides, defined by residues 117-136 of full-length cat G, has bactericidal action against Gram-positive pathogens, such as Staphylococcus aureus. Due to the broad-spectrum antibacterial action of this peptide, we have sought to define the amino acids within its primary sequence required for this activity and have developed variants with improved activity. This review emphasizes the importance of both cationicity and hydrophobicity as necessary characteristics for the antibacterial action of CAPs. It also proposes the strategy that naturally occurring large human CAPs can be dissected to smaller CAPs and then modified to enhance their activity in vitro. This approach could prove beneficial to those interested in developing antimicrobial peptides as therapeutic agents.

Previous work has shown that the carAB operon of Salmonella typhimurium is transcribed from tandem promoters, P1 and P2, that are negatively controlled by pyrimidines and arginine, respectively. The results reported here show that purines also negatively control expression of carAB and that this effect is absent in a purR::Tn10 derivative. Primer-extension experiments established that the purine effect is exerted at P1, thus redefining this promoter as sensitive to both purines and pyrimidines. The results of gel-retardation experiments as well as DNase I and premethylation footprintings indicate that the purine repressor interacts with a PUR box 85 bp upstream of P1. Modification of this PUR box by site-directed mutagenesis abolishes the repression by purines in a carA::lacZ fusion, confirming that this box functions in vivo in purine control of carAB expression.