title: Impact of osmotic stress on protein diffusion in Lactococcus lactis.
abstract: We measured translational diffusion of proteins in the cytoplasm and plasma membrane of the Gram-positive bacterium Lactococcus lactis and probed the effect of osmotic upshift. For cells in standard growth medium the diffusion coefficients for cytosolic proteins (27 and 582 kDa) and 12-transmembrane helix membrane proteins are similar to those in Escherichia coli. The translational diffusion of GFP in L. lactis drops by two orders of magnitude when the medium osmolality is increased by ∼ 1.9 Osm, and the decrease in mobility is partly reversed in the presence of osmoprotectants. We find a large spread in diffusion coefficients over the full population of cells but a smaller spread if only sister cells are compared. While in general the diffusion coefficients we measure under normal osmotic conditions in L. lactis are similar to those reported in E. coli, the decrease in translational diffusion upon osmotic challenge in L. lactis is smaller than in E. coli. An even more striking difference is that in L. lactis the GFP diffusion coefficient drops much more rapidly with volume than in E. coli. We discuss these findings in the light of differences in turgor, cell volume, crowding and cytoplasmic structure of Gram-positive and Gram-negative bacteria.
authors.affiliation: Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre & Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands; Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium.
authors.forename: Jacek T
authors.initials: JT
authors.lastname: Mika
authors.forename: Paul E
authors.initials: PE
authors.lastname: Schavemaker
authors.forename: Victor
authors.initials: V
authors.lastname: Krasnikov
authors.forename: Bert
authors.initials: B
authors.lastname: Poolman
mesh_terms: D002462:Cell Membrane / Q000737:chemistry*; D003470:Culture Media / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry*; D004058:Diffusion; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology; D013294:Lactococcus lactis / Q000187:drug effects* / Q000502:physiology; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D011506:Proteins / Q000032:analysis*
chemical_list: D003470:Culture Media; D011506:Proteins