Extracellular DNA in Biofilms

Abstract

Extracellular DNA (eDNA) is an important biofilm component that was recently discovered. Its presence has been initially observed in biofilms of Pseudomonas aeruginosa, Streptococcus intermedius, Streptococcus mutans, then Enterococcus faecalis and staphylococci. Autolysis is the common mechanism by which eDNA is released. In P. aeruginosa eDNA is generated by lysis of a bacterial subpopulation, under control of quorum sensing system. In E. faecalis autolysis proceeds in a fratricide mode, resulting from a process similar to necrosis of eukaryotic cells. In Staphylococcus aureus autolysis originates by an altruistic suicide, i.e., a programmed cell death similar to apoptosis of eukaryotic cells. In S. aureus autolysis is mediated by murein hydrolase, while in S. epidermidis by the autolysin protein AtlE. In P. aeruginosa eDNA is located primarily in the stalks of mushroom-shaped multicellular structures. In S. aureus the crucial role of eDNA in stabilizing biofilm is highlighted by the disgregating effect of DNase I. eDNA represents an important mechanism for horizontal gene transfer in bacteria. eDNA and other microbial structural motifs are recognized by the innate immune system via the TLR family of pattern recognition receptors (PRRs).

Plasticity of Candida albicans Biofilms

“…The ECM is hydrated and therefore is composed primarily of water. The matrix that supports the gel is composed of structural proteins and polysaccharides and contains extracellular DNA (eDNA) (145)(146)(147)(148)(149)(150)(151). Recently, McCrate et al (152) demonstrated that the ECM of E. coli biofilms contains cellulose and curli proteins, with the latter forming fibrous amyloid bodies.…”

Neutrophil extracellular traps as the main source of eDNA

“…Therefore, the employment of PE-depolymerising agents such as gelsolin and thymosin beta 4 or DNase 1 used for dissolution of biofilm-stimulating F-actin and DNA, respectively, might constitute an interesting approach in the eradication of microbial communities [62][63][64]. The statement that the presence of eDNA is crucial for the biofilm formation and structural integrity is additionally established by the reports demonstrating that the treatment with DNase 1 reduces the attachment of microbial cells to the surface, inhibits the biofilm development, and reduces the mass of mature biofilm [65], which is determined by the impairment of cell-to-cell adhesion and joining elements in microbial aggregates [66,67]. Importantly, the co-administration of antimicrobial agents with factors that have the ability to disassemble the biofilm polyelectrolyte network, including DNase 1, considerably improves their antibacterial efficiency [5,68].…”

“…It has been hypothesised that this phenomenon is determined by the presence of some proteolytic exoenzymes with the ability to deactivate DNase, because this effect is particularly evident in mature biofilm older than ~80 h [66].…”

“…To date, there is evidence confirming that eDNA is a pool for horizontal gene transfer (HTG) for the purpose of genetic recombination of bacterial cells, such as transformation, conjugation, or transduction. Considering the fact that antibiotic resistance may be acquired due to a mutation or an acquisition of resistant genes [66], the presence and high accessibility of eDNA in the biofilm environment provides a readily available gene tool for genetic modifications resulting in the development of antibiotic resistance [66]. Additionally, Wilton et al demonstrated an addi-Neutrophil extracellular traps as the main source of eDNA tional mechanism of eDNA-mediated development of aminoglycoside resistance of Pseudomonas aeruginosa, which is conditioned by acidification of the local biofilm environment, strongly promoting the antibiotic resistant phenotype acquired by modification of lipid A and the synthesis of spermidine on the bacterial outer membrane [71].…”

Nontypeable Haemophilus influenzae releases DNA and DNABII proteins via a T4SS-like complex and ComE of the type IV pilus machinery

“…Some bacteria have a mechanism by which a subpopulation of cells will undergo programmed cell death and lysis to release all of their cellular contents into the environment (9). This type of cell lysis provides common goods for neighboring bacteria and releases DNA for horizontal gene transfer (4,65). Staphylococcus aureus has been shown to undergo such an altruistic cell death (9).…”