Functional analysis of luxS in Staphylococcus aureus reveals a role in metabolism but not quorum sensing.
The function of AI-2 in many bacteria and the physiological role of LuxS, the enzyme responsible for its production, remain matters of debate. Here, we show that in Staphylococcus aureus the luxS gene forms a monocistronic transcriptional unit under the control of a sigma(70)-dependent promoter. The gene was transcribed throughout growth under a variety of conditions, including intracellular growth in MAC-T cells. AI-2 was produced in rich media under aerobic and anaerobic conditions, peaking during the transition to stationary phase, but was hardly detectable in a sulfur-limited defined medium. In the presence of glucose or under anaerobic conditions, cultures retained considerable AI-2 activity after entry into stationary phase. Inactivation of luxS in various S. aureus strains did not affect virulence-associated traits, such as production of hemolysins and extracellular proteases, biofilm formation, and the agr signaling system. Conversely, AI-2 production remained unchanged in an agr mutant. However, luxS mutants grown in a sulfur-limited defined medium exhibited a growth defect. When grown together with the wild type in mixed culture, luxS mutants of various S. aureus strains showed reduced ability to compete for growth under these conditions. In contrast, a complemented luxS mutant grew as well as the parent strain, suggesting that the observed growth defect was of an intracellular nature and had not been caused by either second-site mutations or the lack of a diffusible factor. However, the LuxS/AI-2 system does not appear to contribute to the overall fitness of S. aureus RN6390B during intracellular growth in epithelial cells: the wild type and a luxS mutant showed very similar growth patterns after their internalization by MAC-T cells.
Institute of Infections, Immunity, and Inflammation, University of Nottingham, Centre for Biomolecular Sciences, Nottingham NG7 2RD, United Kingdom.
Neil
N
Doherty
Matthew T G
MT
Holden
Saara N
SN
Qazi
Paul
P
Williams
Klaus
K
Winzer
D000332:Aerobiosis; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development; D013437:Carbon-Sulfur Lyases; D003470:Culture Media / Q000737:chemistry; D012321:DNA-Directed RNA Polymerases / Q000502:physiology; D017353:Gene Deletion; D015870:Gene Expression; D005796:Genes; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D006714:Homoserine / Q000031:analogs & derivatives / Q000096:biosynthesis; D007783:Lactones; D008156:Luciferases / Q000032:analysis / Q000235:genetics; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000502:physiology; D013211:Staphylococcus aureus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D037521:Virulence Factors / Q000032:analysis
D001426:Bacterial Proteins; D003470:Culture Media; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D012808:Sigma Factor; D037521:Virulence Factors; D006714:Homoserine; D008156:Luciferases; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria