Insight into the composition of the intercellular matrix of Streptococcus pneumoniae biofilms

Abstract

Biofilm matrices consist of a mixture of extracellular polymeric substances synthesized in large part by the biofilm-producing microorganisms themselves. These matrices are responsible for the cohesion and three-dimensional architecture of biofilms. The present study demonstrates the existence of a matrix composed of extracellular DNA, proteins and polysaccharides in the biofilm formed by the human pathogen Streptococcus pneumoniae. Extracellular DNA, visualized by fluorescent labelling, was an important component of this matrix. The existence of DNA-protein complexes associated with bacterial aggregates and other polymers was hypothesized based on the unexpected DNA binding activity of lysozyme LytC, a novel moonlighting protein. Actually, a 25-amino-acid-long peptide derived from LytC (positions 408 and 432 of the mature LytC) was also capable of efficiently binding to DNA. Moreover, the presence of intercellular DNA-LytC protein complexes in pneumococcal biofilms was demonstrated by confocal laser scanning microscopy. Evidence of extracellular polysaccharide different from the capsule was obtained by staining with Calcofluor dye and four types of lectin conjugated to Alexa fluorophores, and by incubation with glycoside hydrolases. The presence of residues of Glcp(1→4) and GlcNAc(1→4) (in its deacetylated form) in the pneumococcal biofilm was confirmed by GC-MS techniques.

Minimal Peptidoglycan (PG) Turnover in Wild-Type and PG Hydrolase and Cell Division Mutants of Streptococcus pneumoniae D39 Growing Planktonically and in Host-Relevant Biofilms

“…The extracellular DNA released is thought to act as a major matrix component in the biofilms (65,68). Consistent with this expectation, pneumococcal cells in biofilms formed on fixed epithelial cells were surrounded by a haze of DAPI-stained DNA out-side the host cell nuclei (data not shown).…”

Community surveillance enhances Pseudomonas aeruginosa virulence during polymicrobial infection

“…We favor peptidoglycan as the source of GlcNAc for two additional reasons: more than 25% of the cell wall is shed by Grampositive bacteria during growth, indicating that large amounts of this polymer are shed naturally (52); and P. aeruginosa is highly lytic for Gram-positive bacteria (24,33,36), a process that would further release peptidoglycan fragments into the local environment. Of course other bacterial-produced GlcNAc polymers could potentially serve as sources of GlcNAc, including poly-GlcNAc exopolysaccharide capsules produced by staphylococci and streptococci (53)(54)(55). This is not the first instance in which peptidoglycan acts as a cue to elicit specific cellular responses.…”

Quorum-Sensing Systems LuxS/Autoinducer 2 and Com Regulate Streptococcus pneumoniae Biofilms in a Bioreactor with Living Cultures of Human Respiratory Cells

“…It is possible that autolysis of planktonic cells provides eDNA required for biofilm assembly (29). This eDNA has recently been visualized on the biofilm matrix (54). Biofilm autolysis seen 16 h postinoculation was, in part, controlled by the LuxS/AI-2 and Com QS systems.…”