A novel extracellular vesicle-associated endodeoxyribonuclease helps Streptococcus pneumoniae evade neutrophil extracellular traps and is required for full virulence

Abstract

Streptococcus pneumoniae (pneumococcus) is a major bacterial pathogen that causes pneumonia and septicemia in humans. Pneumococci are cleared from the host primarily by antibody dependent opsonophagocytosis by phagocytes like neutrophils. Neutrophils release neutrophil extracellular traps (NETs) on contacting pneumococci. NETs immobilize pneumococci and restrict its dissemination in the host. One of the strategies utilized by pneumococci to evade the host immune response involves use of DNase(s) to degrade NETs. We screened the secretome of autolysin deficient S. pneumoniae to identify novel DNase(s). Zymogram analysis revealed 3 bands indicative of DNase activity. Mass spectrometric analysis led to the identification of TatD as a potential extracellular DNase. Recombinant TatD showed nucleotide sequence-independent endodeoxyribonuclease activity. TatD was associated with extracellular vesicles. Pneumococcal secretome degraded NETs from human neutrophils. Extracellular vesicle fraction from tatD deficient strain showed little NET degrading activity. Recombinant TatD efficiently degraded NETs. tatD deficient pneumococci showed lower bacterial load in lungs, blood and spleen in a murine sepsis model compared to wildtype strain, and showed less severe lung pathology and compromised virulence. This study provides insights into the role of a novel extracellular DNase in evasion of the innate immune system.

The Brain Entangled: The Contribution of Neutrophil Extracellular Traps to the Diseases of the Central Nervous System

“…These observations correspond with the findings of the clinical study performed by Tillet et al, who noted a 26% decline in mortality from pneumococcal meningitis after addition of DNase to penicillin therapy [68]. Studies detailing the NET-evading mechanisms proved that pneumococci can produce nucleases or modify the cell surface to avoid NET-mediated killing and to further disseminate to other organs [67,69,70]. Another strain of bacteria with the ability to survive in NETs is methicillin-resistant S. aureus [71].…”

State-of-the-art in the pneumococcal field: Proceedings of the 11th International Symposium on Pneumococci and Pneumococcal Diseases (ISPPD-11)

“…This study showed that S. pneumoniae strain D39 increased transcription of competence, pyrimidine and heat shock genes in response to interaction with brain tissue. Jhelum and colleagues [86] also demonstrated that pneumococci have mechanisms to package DNA-degrading enzymes into vesicles, which in turn facilitates the destruction of neutrophil extracellular traps.…”

The Contribution of Membrane Vesicles to Bacterial Pathogenicity in Cystic Fibrosis Infections and Healthcare Associated Pneumonia

“…The MVs are packed with sRNA molecules that bind to mRNA inside human lung cells and in this way quench the human immune response. Similarly, an extracellular DNase was identified in MVs from S. pneumoniae that blocks neutrophil activity and helps to evade the host innate immune response (Jhelum et al, 2018). Porin-loss, which is common in antibioticresistant strains of K. pneumoniae, impacts the MV composition and the host-inflammatory response.…”