DNA uptake by cell wall-deficient bacteria reveals a putative ancient macromolecule uptake mechanism

Abstract

Horizontal gene transfer in bacteria is widely believed to occur via three main mechanisms: conjugation, transduction and transformation. These mechanisms facilitate the passage of DNA across the protective cell wall using sophisticated machinery. We present here a new mechanism of DNA uptake that is independent of canonical DNA uptake machineries and is used by bacteria that live without a cell wall. We show that the cell wall-deficient bacteria engulf extracellular material, whereby intracellular vesicles are formed, and DNA is internalized. This mechanism is not specific to DNA, and allows uptake of other macromolecules and even 125 nm lipid nanoparticles (LNPs). Uptake was prevented by molecules known to inhibit eukaryotic endocytosis, suggesting this to be an energy-dependent process. Given that cell wall-deficient bacteria are considered a model for early life forms, our work provides a possible mechanism for primordial cells to acquire new genetic material or food before invention of the bacterial cell wall.

Light and electron microscopy continuum-resolution imaging of 3D cell cultures

“…Cryo-CLEM for HPF samples still suffers from technical shortcomings, including light scattering when imaging beyond the first few microns from the HPF carrier surface, thus requiring new objectives with working distance ≥ 1mm and with NA > 0.5. In addition, unlike room-temperature approaches, it is not possible to brand the sample surface for precise correlation with FIB-SEM imaging, although new carriers with finder patterns may provide a possible solution (Kapteijn et al, 2022).…”

Precise targeting for 3D cryo-correlative light and electron microscopy volume imaging of tissues using a FinderTOP

“…The cryoFIB/SEM images were processed using the EM processing toolbox of Zen Connect 3.5 (blue edition) to correct for defects such as curtaining, misalignment and local charging, analogous to our previously reported approach 38 , but with keeping the same processing settings for the whole stack. The same software was used for subsequent noise reduction and contrast enhancement.…”