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Published on: October 13, 2015
Mechanism of bacterial outer membrane exchange revealed by quantitative microscopy
Elias J Topo1, Carolina Basurto De Santiago1, Pengbo Cao2,3
1Department of Biology, Texas A&M University, College Station TX 77843, USA.
Abstract:
Kin recognition, the ability to distinguish self from nonself at the cellular level is critical to multicellular life. Myxococcus xanthus is a multicellular bacterium that cooperates among genetically-related cells and reduces exploitation by nonkin through outer membrane exchange (OME) of common goods and toxins. The polymorphic cell surface receptor called TraA and its partner protein TraB mediate kin recognition by OME, but its molecular mechanism remains unknown. Here we used quantitative microscopy techniques to characterize the stoichiometry of the intracellular TraAB complexes and the intercellular TraA-TraA interactions. We visualized the OME of single protein particles between cells and revealed that OME depends on the free diffusion of outer membrane (OM) contents. Based on the predicted structures, we propose a model that TraAB overcomes the repulsion between OMs by stressing the membranes and reducing the contact area, analogous to the eukaryotic soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), which mediate plasma membrane fusion. Our working model provides a novel pathway that leads to an underlying conserved mechanism for membrane fusion that is a foundation process for multicellularity.
Insights
Myxococcus xanthus uses outer membrane exchange (OME) for kin recognition. Researchers propose a model where TraAB proteins mediate this process by reducing membrane contact, similar to eukaryotic membrane fusion mechanisms.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Kin recognition is vital for multicellular organisms, enabling cooperation and preventing exploitation.
- Myxococcus xanthus employs outer membrane exchange (OME) for distinguishing kin from non-kin.
- The molecular mechanism of TraA and TraB in mediating OME remains largely unknown.
Purpose of the Study:
- To elucidate the molecular mechanism of kin recognition mediated by TraA and TraB in Myxococcus xanthus.
- To characterize the stoichiometry of TraAB complexes and intercellular TraA-TraA interactions.
- To investigate the biophysical basis of outer membrane exchange.
Main Methods:
- Quantitative microscopy techniques were employed.
- The stoichiometry of intracellular TraAB complexes was characterized.
- Intercellular TraA-TraA interactions and OME of single protein particles were visualized.
Main Results:
- Outer membrane exchange (OME) was found to depend on the free diffusion of outer membrane contents.
- A model was proposed where TraAB complexes reduce membrane repulsion by decreasing contact area.
- The mechanism is analogous to eukaryotic SNARE-mediated membrane fusion.
Conclusions:
- The study proposes a novel model for TraAB-mediated outer membrane exchange in Myxococcus xanthus.
- This mechanism provides insights into a conserved pathway for membrane fusion, essential for multicellularity.
- The findings contribute to understanding the fundamental processes underlying the evolution of multicellular life.
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