Investigating the molecular basis of the bacterial endocytosis-like protein uptake
Microbial Ecology and Applied Microbiology
Final Report Abstract
In summary the projects revolutionized the concept of the planctomycetal cell plan. Initially, we aimed to reveal the molecular mechanism of endocytosis-like protein uptake in Planctomycetes. However, we soon realized that there was no endocytosis-like uptake and that high molecular weight substrates were not taken up into vesicles but stored in the enlarged periplasmic space instead. Planctomycetes were believed to lack the canonical Gram- negative outer membrane and a peptidoglycan (PG) cell wall. We were able to show that instead Planctomycetes have both, a PG cell wall and a Gram-negative outer membrane. However, this more typical Gram-negative cell plan is counterintuitive to endocytosis which requires inward vesicle formation at the outermost membrane which is prevented by lipopolysaccharides in Gramnegative outer membranes. Thus, uptake must employ another mechanism than endocytosis. However, canonical OMP transport channels are too small to facilitate uptake of complex substrates as used in our study. Thus, a novel unknown mechanism must exist that allows Planctomycetes the fast incorporation of such high molecular weight substrates. We demonstrated evidence that instead of endocytosis, a novel fiber mediated uptake mechanism might be employed. Planctomycetes possess unique donut shaped ring structures within their outer membranes. Such structures are unique among bacteria, and we demonstrated that fiber-like structures originate from crateriform structures. Employing gold labeling of high molecular weight substrates, we further proved that such substrates bind to fibers. We raised the hypothesis that such fibers act as ‘molecular fishing rod’ to harvest for example complex carbon substrates into the periplasmic space where they are subject to degradation. This ‘selfish feeding’ mechanism has the great advantage that multiple enzymes can be accumulated in the enlarged periplasmic space that perform the degradation. Other bacteria secrete such substrates into the environment, a strategy prone to cheating by other, non-enzyme- producing species. Taken together, the projects were very successful and significantly changed our picture of Planctomycetes. The genetic tools developed by Damien Devos’s group will be very instrumental for future in-depth analysis of this novel fiber mediated uptake mechanism.
Publications
- 2015. A multi-functional tubulovesicular network as the ancestral eukaryotic endomembrane system. 2015. Biology 4(2): 264-281
González-Sánchez JC, Costa R, Devos D
(See online at https://dx.doi.org/10.3390/biology4020264) - 2015. Planctomycetes do possess peptidoglycan. Nature Communications. 6: p.7116
Jeske O, Schüler M, Schumann P, Schneider A, Boedeker C, Jogler M, Rohde M, Mayer C, Engelhardt H, Spring S, Jogler C
(See online at https://doi.org/10.1038/ncomms8116) - 2016. Developing of genetic tools for the manipulation of the Planctomycetes. Frontiers in Microbiology. 7:p. 914
Riveras-Marin E, Canosa I, Santero E and Devos D
(See online at https://doi.org/10.3389/fmicb.2016.00914) - 2017. Determining the bacterial cell biology of Planctomycetes. Nature Communications. 10;8: 14853
Boedeker C, Schüler M, Reintjes G, Jeske O, van Teeseling MCF, Jogler M, Rast P, Borchert D, Devos DP, Kucklick M, Schaffer M, Kolter R, van Niftrik L, Engelmann S, Amann R, Rohde M, Engelhardt H and Jogler C
(See online at https://doi.org/10.1038/ncomms14853)
