During the Early Stages of Staphylococcus aureus Biofilm Formation, Induced Neutrophil Extracellular Traps Are Degraded by Autologous Thermonuclease.
Staphylococcus aureus extracellular DNA (eDNA) plays a crucial role in the structural stability of biofilms during bacterial colonization; on the contrary, host immune responses can be induced by bacterial eDNA. Previously, we observed production of S. aureus thermonuclease during the early stages of biofilm formation in a mammalian cell culture medium. Using a fluorescence resonance energy transfer (FRET)-based assay, we detected thermonuclease activity of S. aureus biofilms grown in Iscove's modified Dulbecco's medium (IMDM) earlier than that of widely studied biofilms grown in tryptic soy broth (TSB). The thermonuclease found was Nuc1, confirmed by mass spectrometry and competitive Luminex assay. These results indicate that biofilm development in IMDM may not rely on eDNA for structural stability. A bacterial viability assay in combination with wheat germ agglutinin (WGA) staining confirmed the accumulation of dead cells and eDNA in biofilms grown in TSB. However, in biofilms grown in IMDM, minimal amounts of eDNA were found; instead, polysaccharide intercellular adhesin (PIA) was detected. To investigate if this early production of thermonuclease plays a role in immune modulation by biofilm, we studied the effect of thermonuclease on human neutrophil extracellular trap (NET) formation using a nuc knockout and complemented strain. We confirmed that thermonuclease produced by early-stage biofilms grown in IMDM degraded biofilm-induced NETs. Additionally, neither the presence of biofilms nor thermonuclease stimulated an increase in reactive oxygen species (ROS) production by neutrophils. Our findings indicated that S. aureus, during the early stages of biofilm formation, actively evades the host immune responses by producing thermonuclease.
['Sultan|Andi R|AR|', 'Hoppenbrouwers|Tamara|T|', 'Lemmens-den Toom|Nicole A|NA|', 'Snijders|Susan V|SV|', 'van Neck|Johan W|JW|', 'Verbon|Annelies|A|', 'de Maat|Moniek P M|MPM|', 'van Wamel|Willem J B|WJB|']
D018441:Biofilms D065206:Extracellular Traps D031541:Fluorescence Resonance Energy Transfer D006801:Humans D050296:Microbial Viability D008836:Micrococcal Nuclease D009504:Neutrophils D011135:Polysaccharides, Bacterial D017382:Reactive Oxygen Species D013203:Staphylococcal Infections D013211:Staphylococcus aureus
Staphylococcus aureus biofilm thermonuclease eDNA NETs ROS NETosis early biofilm