ABSTRACT
Nonfilamentous actinobacteria have been less studied as secondary metabolite producers than their filamentous counterparts such as Streptomyces. From our collection of nonfilamentous actinobacteria isolated from sandstone, an Arthrobacter strain was found to produce a new cyclic peptide arthroamide (1) together with the known compound turnagainolide A (2). These compounds inhibited the quorum sensing signaling of Staphylococcus aureus in the submicromolar to micromolar range.
Subject(s)
Arthrobacter/chemistry , Depsipeptides/isolation & purification , Depsipeptides/chemistry , Depsipeptides/pharmacology , Molecular Structure , Quorum Sensing , Staphylococcus aureusABSTRACT
Cyclic peptides are commonly used as quorum-sensing autoinducers in Gram-positive Firmicutes bacteria. Well-studied examples of such molecules are thiolactone and lactone, used to regulate the expression of a series of virulence genes in the agr system of Staphylococcus aureus and the fsr system of Enterococcus faecalis, respectively. Three cyclodepsipeptides WS9326A, WS9326B and cochinmicin II/III were identified as a result of screening actinomycetes culture extracts for activity against the agr/fsr system. These molecules are already known as receptor antagonists, the first two for tachykinin and the last one for endothelin. WS9326A also inhibited the transcription of pfoA regulated by the VirSR two-component system in Clostridium perfringens. Receptor-binding assays using a fluorescence-labeled autoinducer (FITC-GBAP) showed that WS9326A and WS9326B act as receptor antagonists in this system. In addition, an ex vivo assay showed that WS9326B substantially attenuated the toxicity of S. aureus for human corneal epithelial cells. These results suggest that these three natural cyclodepsipeptides have therapeutic potential for targeting the cyclic peptide-mediated quorum sensing of Gram-positive pathogens.
Subject(s)
Actinobacteria/metabolism , Depsipeptides/pharmacology , Gram-Positive Bacteria/drug effects , Lactones/pharmacology , Peptides, Cyclic/metabolism , Quorum Sensing/drug effects , Actinobacteria/chemistry , Bacterial Proteins/genetics , Bacterial Toxins/genetics , Cell Line, Transformed , Clostridium perfringens/drug effects , Clostridium perfringens/genetics , Clostridium perfringens/physiology , Cornea/cytology , Cornea/microbiology , Depsipeptides/isolation & purification , Depsipeptides/metabolism , Enterococcus faecalis/drug effects , Enterococcus faecalis/physiology , Gram-Positive Bacteria/physiology , Hemolysin Proteins/genetics , Hemolysin Proteins/metabolism , Humans , Lactones/isolation & purification , Peptides, Cyclic/chemistry , Peptides, Cyclic/isolation & purification , Peptides, Cyclic/pharmacology , Staphylococcus aureus/drug effects , Staphylococcus aureus/pathogenicity , Staphylococcus aureus/physiology , Virulence/drug effectsABSTRACT
A thiolactone/lactone peptide-mediated quorum sensing (QS) system is commonly employed in gram-positive bacteria to control the expression of a variety of phenotypes, including the production of virulence factors and biofilm formation. Here, we describe assay protocols for the well-studied QS systems (agr and fsr) of two representative gram-positive pathogens, Staphylococcus aureus and Enterococcus faecalis. These convenient assay systems are useful for the screening of QS inhibitors as well as for basic research to address the mechanism of these QS systems.
