Previously, we found that phagocytic cells ingest bacteria directly from the cytosol of infected cells without killing the initially infected cell (Steele et al. 2016). Here, we explored the events immediately following bacterial transfer. Francisella tularensis bacteria acquired from infected cells were found within double-membrane vesicles partially composed from the donor cell plasma membrane. As with phagosomal escape, the F. tularensis Type VI Secretion System (T6SS) was required for vacuole escape. We constructed a T6SS inducible strain and established conditions where this strain is trapped in vacuoles of cells infected through bacterial transfer. Using this strain we identified bacterial transfer events in the lungs of infected mice, demonstrating that this process occurs in infected animals. These data and electron microscopy analysis of the transfer event revealed that macrophages acquire cytoplasm and membrane components of other cells through a process that is distinct from, but related to phagocytosis.
- Thomas H Kawula
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: All animals were handled according to approved institutional animal care and use committee (IACUC) protocol #4946 at Washington State University.
- Sophie Helaine, Imperial College London, United Kingdom
© 2019, Steele et al.
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