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.
Highlights
Bacterial biofilm is defined as an ordered assembly of bacterial cells contained within a polymeric matrix [1,2]
Lysis is important for biofilm adherence It has been established that extracellular genomic DNA (eDNA) released as a result of cell lysis aids in the formation of an adherent staphylococcal biofilm [6,7,14,30]
Despite the presence of similar amounts of bacterial growth, polyanethole sulfonate (PAS) treatment at the zero and two-hour time points resulted in a dramatic reduction in the amount of adherent biomass (Fig. 1) and correlates with lower eDNA levels measured from biofilms grown in the presence of PAS as previously reported [7]
Summary
Bacterial biofilm is defined as an ordered assembly of bacterial cells contained within a polymeric matrix [1,2]. Recent studies demonstrate that the biofilm matrix can be comprised of a variety of important structural components including polysaccharides, proteins, and DNA [3,4,5,6,7,8,9]. The results of a study by Webb et al [17] suggest that bacteriophage-mediated cell death and lysis of P. aeruginosa promotes microcolony development and dispersal. In experiments with Enterococcus faecalis, Thomas et al [12] demonstrated the effects of two secreted proteases, GelE and SprE, on biofilm development. The specific mechanisms controlling cell death and lysis are likely to vary among species, these studies demonstrate that the control of these processes has a significant impact on biofilm development
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