Kudhail, A. | Search bioRxiv

bioRxiv2026

Single-molecule imaging of DNA repair and cytoplasmic rigidification in intracellular bacteria

DNA damage is an important component of the antibacterial response of phagocytes, but which DNA repair mechanisms are active in intracellular bacteria remains unclear. We developed a live-cell single-molecule tracking approach to directly measure DNA repair activity in Escherichia coli within macrophages. Phagocytosis activates bacterial base excision and nucleotide excision repair pathways and increases DNA mismatch repair foci indicative of DNA replication errors. Phagocyte-generated stresses also cause a general slowdown in protein diffusion within bacteria, consistent with a transition of the cytoplasm towards a glass-like state, which is associated with reduced metabolic activity. At the single-cell level, DNA repair activity is highly heterogeneous, with metabolically inactive bacteria showing the greatest engagement of repair proteins. Together, these findings reveal how distinct DNA repair pathways are deployed during macrophage infection and link repair activity to the metabolic and biophysical states of individual intracellular bacteria.

microbiology↗

bioRxiv2023

Phospholipid transport to the bacterial outer membrane through an envelope-spanning bridge

The outer membrane of Gram-negative bacteria provides a formidable barrier, essential for both pathogenesis and antimicrobial resistance. Biogenesis of the outer membrane requires the transport of phospholipids across the cell envelope. Recently, YhdP was implicated as a major protagonist in the transport of phospholipids from the inner membrane to the outer membrane however the molecular mechanism of YhdP mediated transport remains elusive. Here, utilising AlphaFold, we observe YhdP to form an elongated assembly of 60 {beta} strands that curve to form a continuous hydrophobic groove. This architecture is consistent with our negative stain electron microscopy data which reveals YhdP to be approximately 250 [A] in length and thus sufficient to span the bacterial cell envelope. Furthermore, molecular dynamics simulations and in vivo bacterial growth assays indicate essential helical regions at the N- and C-termini of YhdP, that may embed into the inner and outer membranes respectively, reinforcing its envelope spanning nature. Our in vivo crosslinking data reveal phosphate-containing substrates captured along the length of the YhdP groove, providing direct evidence that YhdP transports phospholipids. This finding is congruent with our molecular dynamics simulations which demonstrate the propensity for inner membrane lipids to spontaneously enter the groove of YhdP. Collectively, our results support a model in which YhdP bridges the cell envelope, providing a hydrophobic environment for the transport of phospholipids to the outer membrane.

microbiology↗