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Young/NAS; ~2 g/ V( ~+ F! E3 W% T
7 j, d m. ]$ e* o3 V- D/ vJust before they lyse, bacteria infected with lambda phage have no idea what is about to hit them, according to Angelika Gründling, Mike Manson, and Ry Young of Texas A&M University (College Station, TX). Gründling watched bugs spin around their single tethered flagella as an indicator that their membranes were still energized. The spinning stopped abruptly a few seconds before the cells lysed, thus contradicting the assumptions of one model for lysis timing.
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+ b+ y# z# Z! U; z& x( ]That model was born from the observation that membrane energy poisons induce lysis prematurely. Energy poisons, some suggested, were merely accelerating a normal process of gradual proton leakage. In this model, phage-produced holin proteins would cause the leak, until a critical reduction in proton motive force (pmf) across the membrane triggered any remaining holins to form into pores and finish off the bug.+ }1 {6 I/ @( O: h/ B# U# D9 C
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Gründling's new observations suggest that there may indeed be a critical level of pmf, but that there is no significant leakage early on that would gradually lead the cell to this critical level. Instead, holins increase in concentration until a pore spontaneously precipitates in the membrane. The catastrophic proton leak that results initiates the formation of many other pores, leading to the bug's rapid demise.. M) F) w$ l* H2 N
$ y6 [5 L6 g2 A7 l0 `This triggering mechanism leads not only to rapid and complete lysis, but may also reduce competition from other phage. As new phage attach to a cell, they cause a transient drop in pmf. This drop may trigger holin aggregation, thus killing the cell before the invader has time to start competing with the resident phage.* d6 \# t4 h: Q6 e
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3 [' S2 S) Y* S+ ZGründling, A., et al. 2001. Proc. Natl. Acad. Sci. USA. 10.1073/pnas.151247598 http://www.pnas.org/cgi/content/full/151247598(Phage-infected bacteria rotate (top row)) |
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发表于 2009-3-5 23:37
发表于 2015-5-23 16:15
