Low-Temperature-Induced Changes in Composition and Fluidity of Lipopolysaccharides in the Antarctic Psychrotrophic BacteriumPseudomonas syringae

Abstract

The Antarctic psychrotrophic bacterium Pseudomonas syringae was more sensitive to polymyxin B at a lower (4°C) temperature of growth than at a higher (22°C) temperature. The amount of hydroxy fatty acids in the lipopolysaccharides (LPS) also increased at the lower temperature. These changes correlated with the increase in fluidity of the hydrophobic phase of lipopolysaccharide aggregates in vitro.The outer membrane (OM) of gram-negative bacteria is asymmetric due to the presence of lipopolysaccharides (LPS) exclusively in the outer leaflet and phospholipids in the inner leaflet of the bilayer membrane (17). Accordingly, the hydrophobic interior of the OM is mostly made up of penta-or hexa-acyl chains of lipid A from LPS and the diacyl chains of phospholipids. The packing density of the hydrocarbon chains in the LPS is higher than that of phospholipids (28). Chemically, LPS molecule generally contains, apart from the hydrophobic lipid A, two distinct carbohydrate components: an inner "core oligosaccharide" linked to the lipid A and an outer "O-antigenic chain" of carbohydrate repeat units that is linked to the "core" region (19). The phosphate groups present in the core oligosaccharides and lipid A of LPS bind the divalent cations, such as Ca 2ϩ and Mg 2ϩ , which probably help in stabilizing the outer leaflet of the membrane. It is also known that the LPS layer plays a major role in preventing diffusion of molecules through the OM. The permeation of molecules through the membrane is affected when the LPS leaflet is perturbed by antibiotics such as polymyxin B or by mutations that alters LPS structure (17,18,19). The porin channels located in the OM also regulate the entry of solutes by molecular sieving in bacteria (7,17,19), the exclusion limit being Ͻ600 to 700 Da as seen in Escherichia coli. While these are very important, little is known about the nature and importance of the hydrophobic phase of LPS in regulation of the OM function, especially at a lower temperature of growth.The cytoplasmic membrane of bacteria tends to maintain a "homeoviscous state" for functioning at a lower temperature (27). Three kinds of alterations, namely, increase in the level of unsaturated fatty acids, decrease in the fatty acid chain length, and increase in branching of the chains (24, 25), are mainly known to maintain the "fluidity" or liquid crystalline state of the inner cytoplasmic membrane at lower temperatures. Although similar investigations on the change in OM at a low temperature have been conducted with some mesophilic bacteria (11,16,22,23,31,36), such studies on cold-adapted bacteria do not appear to exist. For this reason, we have initiated some studies with the Antarctic psychrotrophic bacterium Pseudomonas syringae, which has the ability to grow at 0 to 4°C (20,21,26). In this report we examine the alteration in OM property and related compositional change in the LPS of low (4°C)-and high (22°C)-temperature-grown cells of P. syringae and correlate them with the fluidity of the hydrophobic core of LPS aggregates in...

Influence of Growth Temperature on Lipid and Phosphate Contents of Surface Polysaccharides from the Antarctic Bacterium Pseudoalteromonas haloplanktis TAC 125

“…Finally, the increase in the degree of desaturation at lower temperatures is in agreement with findings reported for mesophilic bacteria but in contrast with those reported for a psychrotropic Pseudomonas sp. (11). Therefore, the above data indicate that the structural effects of varying the bacterial growth temperature on the acyl moiety of LOS are more complex than expected.…”

Pore Size Dependence on Growth Temperature Is a Common Characteristic of the Major Outer Membrane Protein OprF in Psychrotrophic and Mesophilic Pseudomonas Species

“…Growth temperature is known to affect several outer membrane components, including lipopolysaccharide in particular, in Pseudomonas species such as P. aeruginosa (23) and P. syringae (24). The phosphorylation of lipopolysaccharide is also temperature dependent; this molecule is more highly phosphorylated at high temperature than at low temperature in P. syringae (34) and P. fluorescens MF0 (10, 13).…”

Characterization and recombinant expression of a divergent ice nucleation protein from ‘Pseudomonas borealis’

“…Reports list more than a dozen microbes that appear to dominate low-temperature consortia and these include Pseudomonas species (WynnWilliams, 1983;Shivaji et al, 1989). Some Pseudomonas strains are known to degrade hydrocarbon spills, particularly in the Arctic (Stallwood et al, 2005), valuable 'cold enzymes' have been isolated from others (Villeret et al, 1997;Cavicchioli, 2002), and membranes of some strains have enhanced fluidity at low temperatures (Kumar et al, 2002). Strains of P. syringae are well known for their INPs, and this phenotype might also be considered a lowtemperature adaptation.…”