Autolysin

About: Autolysin is a research topic. Over the lifetime, 556 publications have been published within this topic receiving 28359 citations.

Staphylococcus and biofilms.

Abstract: Summary The genetic and molecular basis of biofilm formation in staphylococci is multifaceted. The ability to form a biofilm affords at least two properties: the adherence of cells to a surface and accumulation to form multilayered cell clusters. A trademark is the production of the slime substance PIA, a polysaccharide composed of β-1,6-linked N-acetylglucosamines with partly deacetylated residues, in which the cells are embedded and protected against the host’s immune defence and antibiotic treatment. Mutations in the corresponding biosynthesis genes (ica operon) lead to a pleiotropic phenotype; the cells are biofilm and haemagglutination negative, less virulent and less adhesive on hydrophilic surfaces. ica expression is modulated by various environmental conditions, appears to be controlled by SigB and can be turned on and off by insertion sequence (IS) elements. A number of biofilm-negative mutants have been isolated in which polysaccharide intercellular adhesin (PIA) production appears to be unaffected. Two of the characterized mutants are affected in the major autolysin (atlE) and in D-alanine esterification of teichoic acids (dltA). Proteins have been identified that are also involved in biofilm formation, such as the accumulation-associated protein (AAP), the clumping factor A (ClfA), the staphylococcal surface protein (SSP1) and the biofilm-associated protein (Bap). Concepts for the prevention of obstinate polymer-associated infections include the search for new anti-infectives active in biofilms and new biocompatible materials that complicate biofilm formation and the development of vaccines.

Evidence for autolysin-mediated primary attachment of Staphylococcus epidermidis to a polystyrene surface.

Abstract: Summary Biofilm formation on a polymer surface which involves initial attachment and accumulation in multilayered cell clusters (intercellular adhesion) is proposed to be the major pathogenicity factor in Staphylococcus epidermidis foreign-body-associated infections. We have characterized two distinct classes of biofilmnegative Tn917 mutants in S. epidermidis affected in initial attachment (class A) or intercellular adhesion (class B). mut1 (class A mutant) lacks five surfaceassociated proteins with molecular masses of 120, 60, 52, 45 and 38 kDa and could be complemented by transformation with a 16.4 kb wild-type DNA fragment. The complemented mutant was able to attach to a polystyrene surface, to form a biofilm, and produced all of the proteins missing from mut1. Subcloning experiments revealed that the 60 kDa protein is sufficient for initial attachment. Immunofluorescence microscopy using an antiserum raised against the 60 kDa protein showed that this protein is located at the cell surface. DNA-sequence analysis of the complementing region revealed a single open reading frame which consists of 4005 nucleotides and encodes a deduced protein of 1335 amino acids with a predicted molecular mass of 148 kDa. The amino acid sequence exhibits a high similarity (61% identical amino acids) to the atl gene product of Staphylococcus aureus, which represents the major autolysin; therefore the open reading frame was designated atlE. By analogy with the S. aureus autolysin, AtlE is composed of two bacteriolytically active domains, a 60 kDa amidase and a 52 kDa glucosaminidase domain, generated by proteolytic processing. The 120 kDa protein missing from mut1 presumably represents the unprocessed amidase and glucosaminidase domain after proteolytic cleavage of the signal- and propeptide. The 45 and 38 kDa proteins are probably the degradation products of the 60 and 52 kDa proteins, respectively. Additionally, AtlE was found to exhibit vitronectin-binding activity, indicating that AtlE plays a role in binding of the cells not only to a naked polystyrene surface during early stages of adherence, but also to plasma protein-coated polymer surfaces during later stages of adherence. Our findings provide evidence for a new function of an autolysin (AtlE) in mediating the attachment of bacterial cells to a polymer surface, representing the prerequisite for biofilm formation.

Programmed Death in Bacteria

Abstract: Programmed cell death (PCD) in bacteria plays an important role in developmental processes, such as lysis of the mother cell during sporulation of Bacillus subtilis and lysis of vegetative cells in fruiting body formation of Myxococcus xanthus. The signal transduction pathway leading to autolysis of the mother cell includes the terminal sporulation sigma factor EςK, which induces the synthesis of autolysins CwlC and CwlH. An activator of autolysin in this and other PCD processes is yet to be identified. Autolysis plays a role in genetic exchange in Streptococcus pneumoniae, and the gene for the major autolysin, lytA, is located in the same operon with recA. DNA from lysed cells is picked up by their neighbors and recombined into the chromosome by RecA. LytA requires an unknown activator controlled by a sensory kinase, VncS. Deletion of vncS inhibits autolysis and also decreases killing by unrelated antibiotics. This observation suggests that PCD in bacteria serves to eliminate damaged cells, similar to apoptosis of defective cells in metazoa. The presence of genes affecting survival without changing growth sensitivity to antibiotics (vncS, lytA, hipAB, sulA, and mar) indicates that bacteria are able to control their fate. Elimination of defective cells could limit the spread of a viral infection and donate nutrients to healthy kin cells. An altruistic suicide would be challenged by the appearance of asocial mutants without PCD and by the possibility of maladaptive total suicide in response to a uniformly present lethal factor or nutrient depletion. It is proposed that a low rate of mutation serves to decrease the probability that asocial mutants without PCD will take over the population. It is suggested that PCD is disabled in persistors, rare cells that are resistant to killing, to ensure population survival. It is suggested that lack of nutrients leads to the stringent response that suppresses PCD, producing a state of tolerance to antibiotics, allowing cells to discriminate between nutrient deprivation and unrepairable damage. High levels of persistors are apparently responsible for the extraordinary survival properties of bacterial biofilms, and genes affecting persistence appear to be promising targets for development of drugs aimed at eradicating recalcitrant infections. PCD in unicellular eukaryotes is also considered, including aging in Saccharomyces cerevisiae. Apoptosis-like elimination of defective cells in S. cerevisiae and protozoa suggests that all unicellular life forms evolved altruistic programmed death that serves a variety of useful functions.

Contribution of novel choline‐binding proteins to adherence, colonization and immunogenicity of Streptococcus pneumoniae

Abstract: The surface of Streptococcus pneumoniae is decorated with a family of choline-binding proteins (CBPs) that are non-covalently bound to the phosphorylcholine of the teichoic acid. Two examples (PspA, a protective antigen, and LytA, the major autolysin) have been well characterized. We identified additional CPBs and characterized a new CBP, CbpA, as an adhesin and a determinant of virulence. Using choline immobilized on a solid matrix, a mixture of proteins from a pspA-deficient strain of pneumococcus was eluted in a choline-dependent fashion. Antisera to these proteins passively protected mice challenged in the peritoneum with a lethal dose of pneumococci. The predominant component of this mixture, CbpA, is a 75-kDa surface-exposed protein that reacts with human convalescent antisera. The deduced sequence from the corresponding gene showed a chimeric architecture with a unique N-terminal region and a C-terminal domain consisting of 10 repeated choline-binding domains nearly identical to PspA. A cbpA-deficient mutant showed a >50% reduction in adherence to cytokine-activated human cells and failed to bind to immobilized sialic acid or lacto-N-neotetraose, known pneumococcal ligands on eukaryotic cells. Carriage of this mutant in an animal model of nasopharyngeal colonization was reduced 100-fold. There was no difference between the parent strain and this mutant in an intraperitoneal model of sepsis. These data for CbpA extend the important functions of the CBP family to bacterial adherence and identify a pneumococcal vaccine candidate.

Role of autolysin-mediated DNA release in biofilm formation of Staphylococcus epidermidis

Abstract: Staphylococcus epidermidis has become a serious nosocomial pathogen frequently causing infections associated with implanted foreign materials. Biofilm formation is considered a major factor determining S. epidermidis pathogenicity in such device-associated infections. Here, evidence is presented that extracellular DNA is important for the initial phase of biofilm development by S. epidermidis on polystyrene or glass surfaces under static or hydrodynamic conditions. Comparative PCR amplification from S. epidermidis chromosomal and extracellular DNA indicated that the extracellular DNA is similar to chromosomal DNA. Experiments involving the S. epidermidis wild-type and an isogenic atlE mutant indicated that most of the extracellular DNA in S. epidermidis cultures and biofilms is generated through activity of the autolysin AtlE. The presented results suggest that extracellular DNA is generated in S. epidermidis populations through AtlE-mediated lysis of a subpopulation of the bacteria, and that the extracellular DNA promotes biofilm formation of the remaining population.