Modulation of eDNA Release and Degradation Affects Staphylococcus aureus Biofilm Maturation

Abstract

Recent studies have demonstrated a role for Staphylococcus aureus cidA-mediated cell lysis and genomic DNA release in biofilm adherence. The current study extends these findings by examining both temporal and additional genetic factors involved in the control of genomic DNA release and degradation during biofilm maturation. Cell lysis and DNA release were found to be critical for biofilm attachment during the initial stages of development and the released DNA (eDNA) remained an important matrix component during biofilm maturation. This study also revealed that an lrgAB mutant exhibits increased biofilm adherence and matrix-associated eDNA consistent with its proposed role as an inhibitor of cidA-mediated lysis. In flow-cell assays, both cid and lrg mutations had dramatic effects on biofilm maturation and tower formation. Finally, staphylococcal thermonuclease was shown to be involved in biofilm development as a nuc mutant formed a thicker biofilm containing increased levels of matrix-associated eDNA. Together, these findings suggest a model in which the opposing activities of the cid and lrg gene products control cell lysis and genomic DNA release during biofilm development, while staphylococcal thermonuclease functions to degrade the eDNA, possibly as a means to promote biofilm dispersal.

How Staphylococcus aureus biofilms develop their characteristic structure

“…It is possible that enzymes that degrade biofilm polymers provide additional structuring for which there is some recent evidence in S. aureus (7,8); however, how such enzymes contribute to biofilm maturation awaits in-depth investigation. Furthermore, our study suggests that targeting biofilm-structuring surfactant molecules might represent a promising approach to prevent the formation of viable medical and environmental biofilms, although the species-specific chemical nature of these molecules would likely require a specific form of interference in every case.…”

“…Enzymes that degrade essential biofilm polymers may theoretically contribute to biofilm detachment; however, there is only preliminary evidence for such enzyme function in S. aureus or other staphylococci (7,8). In contrast, there are reports indicating that several bacteria use surfactant-like molecules to structure and detach biofilms, which include Bacillus subtilis surfactin (9, 10), Pseudomonas aeruginosa rhamnolipid (11,12), and the phenolsoluble modulin (PSM) β-peptides in Staphylococcus epidermidis, a close relative of S. aureus (4).…”

Genome-wide screen for genes involved in eDNA release during biofilm formation by Staphylococcus aureus

“…Cells of the pooled mutant library were grown under biofilm-inducing conditions, and biofilms were harvested at 6 and 8 h. Preliminary studies had indicated that eDNA release is at its peak during this window (12). Because of the potential risk of population bottlenecks stemming from varying representation of the mutant library in different experiments, the experiment was repeated at both time points.…”

Phage-induced lysis enhances biofilm formation in Shewanella oneidensis MR-1

“…Other factors implicated in cell lysis are toxin/antitoxin system that have been characterized, for example, in Enterococcus faecalis (Thomas et al, 2008) and Staphylococcus sp. (Qin et al, 2007;Rice et al, 2007;Mann et al, 2009). However, a role for toxin/antitoxin systems in biofilm formation is not necessarily directly linked to cell lysis, as has been demonstrated for E. coli (Kim et al, , 2010.…”

“…In contrast, the significance of eDNA for cellular attachment and structural integrity has more recently been recognized for an increasing number of Gram-negative and Grampositive species (Whitchurch et al, 2002;Steinberger and Holden, 2005;Allesen-Holm et al, 2006;Moscoso et al, 2006;Jurcisek and Bakaletz, 2007;Qin et al, 2007;Izano et al, 2008;Thomas et al, 2008;Heijstra et al, 2009;Vilain et al, 2009;Harmsen et al, 2010;Lappann et al, 2010). Release of DNA in bacterial biofilms has mainly been attributed to the lysis of a cellular subpopulation, mediated by the activity of autolysis systems (Allesen-Holm et al, 2006;Rice et al, 2007;Thomas et al, 2008Thomas et al, , 2009Mann et al, 2009). The analysis of aggregates formed by S. oneidensis MR-1 in planktonic cultures indicated the presence of proteins, a-D-mannose or a-D-glucose containing exopolysaccharides, and substantial amounts of eDNA (McLean et al, 2008b).…”