Extracellular lipopolysaccharide production by Erwinia carotovora

A Multiscale Agent-Based Model for the Investigation of E. coli K12 Metabolic Response During Biofilm Formation

Bacterial biofilm formation is an organized collective response to biochemical cues that enables bacterial colonies to persist and withstand environmental insults. We developed a multiscale agent-based model that characterizes the intracellular, extracellular, and cellular scale interactions that modulate Escherichia coli MG1655 biofilm formation. Each bacterium's intracellular response and cellular state were represented as an outcome of interactions with the environment and neighboring bacteria. In the intracellular model, environment-driven gene expression and metabolism were captured using statistical regression and Michaelis-Menten kinetics, respectively. In the cellular model, growth, death, and type IV pili- and flagella-dependent movement were based on the bacteria's intracellular state. We implemented the extracellular model as a three-dimensional diffusion model used to describe glucose, oxygen, and autoinducer 2 gradients within the biofilm and bulk fluid. We validated the model by comparing simulation results to empirical quantitative biofilm profiles, gene expression, and metabolic concentrations. Using the model, we characterized and compared the temporal metabolic and gene expression profiles of sessile versus planktonic bacterial populations during biofilm formation and investigated correlations between gene expression and biofilm-associated metabolites and cellular scale phenotypes. Based on our in silico studies, planktonic bacteria had higher metabolite concentrations in the glycolysis and citric acid cycle pathways, with higher gene expression levels in flagella and lipopolysaccharide-associated genes. Conversely, sessile bacteria had higher metabolite concentrations in the autoinducer 2 pathway, with type IV pili, autoinducer 2 export, and cellular respiration genes upregulated in comparison with planktonic bacteria. Having demonstrated results consistent with in vitro static culture biofilm systems, our model enables examination of molecular phenomena within biofilms that are experimentally inaccessible and provides a framework for future exploration of how hypothesized molecular mechanisms impact bulk community behavior.

Detection of Low Molecular Size Lipopolysaccharide Contaminated in Dialysates used for Hemodialysis Therapy with Polyacrylamide Gel Electrophoresis in the Presence of Sodium Deoxycholate

Dialysis membranes are generally considered to be impermeable for bacterial endotoxin (lipopolysaccharide, LPS) contaminated in dialysates used for hemodialysis therapy, since LPS molecular size in aqueous media has been reported to be more than 106. However, there are few reports concerning its size in dialysates. We have already presented a newly developed polyacrylamide gel electrophoresis with sodium deoxycholate (DOC-PAGE) which proves the LPS size. Using this method, therefore, we attempted to clarify the size of LPS in dialysates. We demonstrated that LPS in dialysates had roughly two different molecular sizes with DOC-PAGE and that compared to migration profiles of Salmonella LPS as controls on DOC-PAGE, one molecular size of LPS was approximately 4,000 and the other in tens of thousands. This investigation indicates the possibility of LPS transfer across dialysis membranes.

Physico-chemical and biophysical study of the interaction of hexa- and heptaacyl lipid A from Erwinia carotovora with magainin 2-derived antimicrobial peptides

The neutralization of endotoxin structures such as the active 'endotoxic principle' lipid A by suitable compounds has been shown to be a key step in the treatment of infectious diseases, in particular in the case of Gram-negative bacteria which frequently may lead to the septic shock syndrome. An effective antimicrobial peptide, originally found in the skin of an African frog, is magainin 2. Here, the interaction of magainin 2-amide and a peptide derived thereof, M2V, with chemically defined and homogeneous hexaacyl and heptaacyl lipids A isolated from LPS of Erwinia carotovora, was investigated. By using Fourier-transform infrared spectroscopy, the gel to liquid crystalline phase transition of the acyl chains of lipid A and the conformation of their phosphate groups due to peptide binding was investigated. The former parameter was also determined by using differential scanning calorimetry. The electrophoretic mobility of lipid A aggregates under the influence of the peptides was studied to determine the Zeta potential, and small-angle X-ray scattering was applied for the elucidation of the types of aggregate structures in the absence and presence of the peptides. The lipid A-induced cytokine production in human mononuclear cells shows that the ability of the two peptides to inhibit a tumor necrosis factor-alpha production correlates with characteristic changes of the biophysical parameters. These are much stronger expressed for the peptide M2V than for magainin 2-amide, which apparently is connected with the higher number of positive as well as more hydrophobic amino acids, leading to a stronger amphiphilicity necessary to neutralize the amphiphilic lipid A aggregates.

Physico-chemical analysis of lipid A fractions of lipopolysaccharide from Erwinia carotovora in relation to bioactivity

Highly purified bisphosphoryl, monophosphoryl and dephosphoryl lipids A from Erwinia carotovora with different acylation patterns were characterized physico-chemically. Applying matrix assisted laser desorption/ionization mass spectrometry, the purity of the lipid A fractions was determined, and from monolayer measurements the molecular space requirement was estimated. Fourier transform infrared spectroscopy allowed the elucidation of the gel to liquid crystalline phase transition of the acyl chains as well as the determination of the tilt angle of the diglucosamine backbone with respect to the acyl chain direction applying dichroitic measurements with attenuated total reflectance. With synchrotron radiation small-angle X-ray diffraction the supramolecular aggregate structure was determined, and with fluorescence resonance energy transfer spectroscopy the lipopolysaccharide binding protein induced intercalation of lipid A into a phospholipid matrix corresponding to that of the macrophage membrane was investigated. From the results, a clear dependence of the physico-chemical parameters on the particular lipid A structure can be followed. Furthermore, these parameters correlate well with the biological activities of the various lipids A as deduced from their ability to induce biological activity (Limulus assay and cytokine induction in mononuclear cells). These results contribute to a closer interpretation of the physico-chemical prerequisites for endotoxic activity as found for enterobacterial lipid A.

Elucidation of the structure of the core region and the complete structure of the R-type lipopolysaccharide of Erwinia carotovora FERM P-7576

An R-type lipopolysaccharide (LPS) from Erwinia carotovora strain FERM P-7576 was studied after strong alkaline degradation and mild acid hydrolysis. The resulting products were analyzed by fast-atom bombardment mass spectrometry, one- and two-dimensional 1H and 13C NMR spectroscopy, dephosphorylation and methylation analysis. The following structure was proposed for the core region of the LPS: [formula in text] where Hep is L-glycero-D-manno-heptose and Kdo is 3-deoxy-D-manno-octulosonic acid. Some LPS species lack the beta-D-Galp residue or the beta-D-Galp-(1-->7)-alpha-Hepp disaccharide. With the known structures of lipid A [Fukuoka, S., Kamishima, H., Nagawa, Y., Nakanishi, H., Ishikawa, K., Niwa, Y., Tamiya, E. & Karube, I. (1992) Arch. Microbiol. 157, 311-318] and the core moiety, the complete LPS structure was established and confirmed by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of the native and O-deacylated LPS.

Influence of cationic antibiotics on phase behavior of rough-form lipopolysaccharide

The rough-form lipopolysaccharide (LPS) interacted with cationic antibiotic polymyxin B and gramicidin S in solution, and showed altered thermotropic phase behavior and viscoelasticity. The phase behavior was measured by differential scanning calorimetry and quartz crystal microbalance (QCM). Addition of polymyxin B of up to 0.5 mg/mL to the 5.0 mg/mL LPS solution increased gel-to-liquid crystalline phase transition enthalpy (delta H) and raised the transition temperature (tmax). The further addition of polymyxin B reduced the delta H value. Gramicidin S produced a different effect, whereby a minor addition reduced tmax and delta H value of the LPS. The LPS film on the platinum electrode of the QCM indicated a downward shift of resonant frequency and an upward shift of resonant resistance when in contact with the antibiotic solution. An interpretation of these variations is that the LPS on the QCM electrode changed not only film weight, but also viscoelasticity owing to contact with the antibiotic solution. The different effects between the antibiotics between polymyxin B and gramicidin S on the LPS are induced by the difference of the governing effect. Polymyxin B interacts with the LPS electrostatically, whereas gramicidin S interacts by hydrophobic moieties.

Facile isolation of endo-pectate lyase from Erwinia carotovora based on electrostatic interaction

Endo-pectate lyase (PATE) from Erwinia carotovora was selectively cosedimented with extracellularly produced lipopolysaccharide-lipid complex (LPSLC) through dialysis of the cell free culture broth. The selective isolation of PATE was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The cosedimentation of the PATE with LPSLC was initiated by decreasing conductivity of the solution and terminated at approx 1 m siemens (mScm-1). As much as 62% of PATE activity in the culture broth was removed by precipitation. PATE was isolated from the precipitate by gel chromatography. The cosedimentation of PATE with LPSLC was remarkably affected by pH or ionic strength. The addition of polycationic peptide polymyxin B sulfate or a metal chloride affected the interaction. The cosedimentation was diminished by acetylation of the free amino groups of PATE. From these results, it was confirmed that the cosedimentation was induced by electrostatic interaction.