title: Perturbation of bacterial ice nucleation activity by a grass antifreeze protein.
abstract: Certain plant-associating bacteria produce ice nucleation proteins (INPs) which allow the crystallization of water at high subzero temperatures. Many of these microbes are considered plant pathogens since the formed ice can damage tissues, allowing access to nutrients. Intriguingly, certain plants that host these bacteria synthesize antifreeze proteins (AFPs). Once freezing has occurred, plant AFPs likely function to inhibit the growth of large damaging ice crystals. However, we postulated that such AFPs might also serve as defensive mechanisms against bacterial-mediated ice nucleation. Recombinant AFP derived from the perennial ryegrass Lolium perenne (LpAFP) was combined with INP preparations originating from the grass epiphyte, Pseudomonas syringae. The presence of INPs had no effect on AFP activity, including thermal hysteresis and ice recrystallization inhibition. Strikingly, the ice nucleation point of the INP was depressed up to 1.9°C in the presence of LpAFP, but a recombinant fish AFP did not lower the INP-imposed freezing point. Assays with mutant LpAFPs and the visualization of bacterially-displayed fluorescent plant AFP suggest that INP and LpAFP can interact. Thus, we postulate that in addition to controlling ice growth, plant AFPs may also function as a defensive strategy against the damaging effects of ice-nucleating bacteria.
authors.affiliation: Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Tomalty
authors.affiliation: Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada. Electronic address: walkervk@queensu.ca.
authors.forename: Virginia K
authors.initials: VK
authors.lastname: Walker
mesh_terms: D021301:Antifreeze Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001681:Biological Assay; D003460:Crystallization; D005615:Freezing; D015870:Gene Expression; D007053:Ice; D007700:Kinetics; D008129:Lolium / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D044224:Pseudomonas syringae / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D021301:Antifreeze Proteins; D001425:Bacterial Outer Membrane Proteins; D007053:Ice; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C063113:ice nucleation protein
keywords: Antifreeze proteins; Ice binding proteins; Ice nucleation proteins; Plant pathogen defence