Differences in cell-associated and cell-free microbial DNA in blood

Area of Science:

• Microbiology
• Genomics
• Medical Diagnostics

Background:

• Traditionally, blood was considered microbe-free in the absence of infection.
• Advances in sequencing reveal microbial DNA in blood, necessitating further investigation.
• The presence and origin of microbial DNA in blood require comprehensive characterization.

Purpose of the Study:

• To characterize microbial DNA in different blood fractions (plasma, red blood cells, buffy coat).
• To determine if microbial DNA in blood is cell-free or associated with cells.
• To explore the potential of blood microbial DNA as a biomarker for diseases like prostate cancer.

Main Methods:

• Blood fractionation into plasma, red blood cells, and buffy coat.
• DNase treatment to assess cell-free microbial DNA.
• Digital droplet PCR for 16S rRNA gene quantification.
• Synthetic full-length 16S rRNA gene sequencing for taxonomic identification.

Main Results:

• The majority of microbial DNA in blood is cell-free, suggesting it does not represent actively replicating microbes.
• The buffy coat fraction showed the lowest 16S rRNA gene copies but the highest diversity of microbial genera.
• Disease-associated compositional differences in microbial DNA were observed in plasma and buffy coat fractions of men with prostate cancer.

Conclusions:

• Microbial DNA in blood is predominantly cell-free.
• The buffy coat fraction is a valuable component for studying blood microbial DNA.
• Blood microbial DNA shows potential as a diagnostic biomarker, with disease-specific variations detected, warranting further large-scale studies.