Lysine acetylation regulates many eukaryotic cellular processes, but its function in prokaryotes is largely unknown. We demonstrated that central metabolism enzymes in Salmonella were acetylated extensively and differentially in response to different carbon sources, concomitantly with changes in cell growth and metabolic flux. The relative activities of key enzymes controlling the direction of glycolysis versus gluconeogenesis and the branching between citrate cycle and glyoxylate bypass were all regulated by acetylation. This modulation is mainly controlled by a pair of lysine acetyltransferase and deacetylase, whose expressions are coordinated with growth status. Reversible acetylation of metabolic enzymes ensure that cells respond environmental changes via promptly sensing cellular energy status and flexibly altering reaction rates or directions. It represents a metabolic regulatory mechanism conserved from bacteria to mammals.

Biofilms play an important role in many chronic bacterial infections. Production of an extracellular mixture of sugar polymers called exopolysaccharide is characteristic and critical for biofilm formation. However, there is limited information about the mechanisms involved in the biosynthesis and modification of exopolysaccharide components and how these processes influence bacterial pathogenesis. Staphylococcus epidermidis is an important human pathogen that frequently causes persistent infections by biofilm formation on indwelling medical devices. It produces a poly-N-acetylglucosamine molecule that emerges as an exopolysaccharide component of many bacterial pathogens. Using a novel method based on size exclusion chromatography-mass spectrometry, we demonstrate that the surface-attached protein IcaB is responsible for deacetylation of the poly-N-acetylglucosamine molecule. Most likely due to the loss of its cationic character, non-deacetylated poly-acetylglucosamine in an isogenic icaB mutant strain was devoid of the ability to attach to the bacterial cell surface. Importantly, deacetylation of the polymer was essential for key virulence mechanisms of S. epidermidis, namely biofilm formation, colonization, and resistance to neutrophil phagocytosis and human antibacterial peptides. Furthermore, persistence of the icaB mutant strain was significantly impaired in a murine model of device-related infection. This is the first study to describe a mechanism of exopolysaccharide modification that is indispensable for the development of biofilm-associated human disease. Notably, this general virulence mechanism is likely similar for other pathogenic bacteria and constitutes an excellent target for therapeutic maneuvers aimed at combating biofilmassociated infection. Exopolysaccharide (EPS)1 is a key component of the biofilm matrix in many biofilm-forming bacteria and may be composed of various sugar polymers (1). It has an important role in immune evasion and tolerance toward antibacterial agents. By far most known EPS molecules are neutral or polyanionic (2). Enzymatic alteration of EPS is believed to significantly change its physicochemical properties and, thus, biofilm structure. However, particularly in Gram-positive bacteria, EPS-modifying enzymes and the relationship between the composition of EPS and its biological function have remained poorly characterized.The Gram-positive bacterium Staphylococcus epidermidis is the most prevalent pathogen involved in hospital-acquired infections (3). The costs related to infections caused by S. epidermidis in the hospital setting are enormous and represent a major health care burden. Most infections caused by S. epidermidis occur after the insertion of indwelling devices such as catheters or prosthetic heart valves. In these cases, the ability of S. epidermidis to form biofilms represents the most important virulence determinant (3). In a biofilm, the bacteria are dramatically less susceptible to antibiotic treatment and attacks by innate host defense. For these reasons, S. ...

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Infections with the leading nosocomial pathogen Staphylococcus epidermidis are characterized by biofilm development on indwelling medical devices. We demonstrate that the quorum-sensing regulator agr affects the biofilm development of S. epidermidis in an unexpected fashion and is likely involved in promoting biofilm detachment. An isogenic agr mutant showed increased biofilm development and colonization in a rabbit model. In addition, nonfunctional agr occurred more frequently among strains isolated from infections of joint prostheses. Lack of functionality was based on mutations, including insertion of an IS256 element. Relative to other bacterial pathogens, quorum sensing in S. epidermidis thus has a different role during biofilm development and biofilm-associated infection. Our results indicate that disabling agr likely enhances the success of S. epidermidis during infection of indwelling medical devices. The permanent elimination of quorum-sensing regulation used by S. epidermidis represents a surprising and unusual means to adapt to a certain environment and type of infection.