Abstract
ABSTRACTBacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels. We recently described an extracellular Pi buffer which appears to counteract the gradient required for Pi diffusion. Here, we demonstrate that various treatments to outer membrane (OM) constituents do not affect the buffered Pi because bacteria accumulate Pi in the periplasm, from which it can be removed hypo-osmotically. The periplasmic Pi can be gradually imported into the cytoplasm by ATP-powered transport, however, the proton motive force (PMF) is not required to keep Pi in the periplasm. In contrast, the accumulation of Pi into the periplasm across the OM is PMF-dependent and can be enhanced by light energy. Because the conventional mechanism of Pi-specific transport cannot explain Pi accumulation in the periplasm we propose that periplasmic Pi anions pair with chemiosmotic cations of the PMF and millions of accumulated Pi pairs could influence the periplasmic osmolarity of marine bacteria.
Highlights
Bacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels
There are the three known bacterial transport systems to import Pi from the periplasm into the cytoplasm: a low affinityhigh velocity phosphate inorganic transport (Pit) system, a low affinity-high velocity Na-dependent phosphate transport (Npt) system and a high affinity-low velocity phosphate-specific transport (Pst) system[15,16,17]
Pi clearance rates of oceanic SAR11, Prochlorococcus and Synechococcus cells vary by orders of magnitude in the patchily Pi-depleted North Atlantic (Supplementary Figs. 1 and 2a, and Supplementary Table 2)
Summary
Bacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels. Marine bacteria, which typically have two membranes (and stain Gram negative), acquire Pi using a diffusion gradient between the environment and the periplasm[10,11] In their cells, the periplasm is separated from the environment by the outer membrane (OM), whose permeability to small, hydrophilic solutes is controlled mainly by hydrated channels—porins (Fig. 1a†). - PstCAB transporter - Peptidoglycan gel - Membrane potential - Osmotic pressure - ATPase cyanobacteria (Supplementary Table 1) with an estimated periplasmic depth[21] of 10−8 m, is only about 2 × 10−17 l In such a tiny volume, the presence of only a few free Pi molecules would exceed the threshold 10−7 mol l−1 Pi concentration (Fig. 1a†)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call