ABSTRACT
It is well established that bacteria are able to respond to temporal gradients (e.g., by chemotaxis). However, it is widely held that prokaryotes are too small to sense spatial gradients. This contradicts the common observation that the vast majority of bacteria live on the surface of a solid substrate (e.g., as a biofilm). Herein we report direct experimental evidence that the nonmotile bacterium Staphylococcus aureus possesses a tactile response, or primitive sense of touch, that allows it to respond to spatial gradients. Attached cells recognize their substrate interface and localize adhesins toward that region. Braille-like avidity maps reflect a cell's biochemical sensory response and reveal ultrastructural regions defined by the actual binding activity of specific proteins.
Subject(s)
Staphylococcus aureus/physiology , Adhesins, Bacterial/chemistry , Adhesins, Bacterial/genetics , Adhesins, Bacterial/physiology , Bacterial Adhesion/physiology , Biofilms/growth & development , Biophysical Phenomena , Fibronectins/chemistry , Fibronectins/genetics , Fibronectins/physiology , Microscopy, Atomic Force , Models, Biological , Protein Interaction Domains and Motifs , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Staphylococcus aureus/genetics , Surface PropertiesABSTRACT
Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospirillum sp. AMB-1 as a model system, we show that magnetosome vesicles exist in the absence of magnetite, biomineralization of magnetite proceeds simultaneously in multiple vesicles, and biomineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation of functional magnetosome vesicles and displays a dynamic subcellular localization throughout the growth cycle of magnetotactic bacteria. Together, these results suggest that the magnetosome precisely coordinates magnetite biomineralization and can serve as a model system for the study of organelle biogenesis in noneukaryotic cells.
Subject(s)
Bacterial Proteins/metabolism , Cytoplasmic Vesicles/metabolism , Iron/metabolism , Magnetospirillum/metabolism , Oxides/metabolism , Bacterial Proteins/genetics , Ferrosoferric Oxide , Genes, Reporter , Magnetospirillum/genetics , Molecular Sequence Data , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Sequence Deletion , Time FactorsABSTRACT
Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter. The silane alcoholysis reaction is an effective method for the regioselective silylation of methyl and phenyl glycosides and generates hydrogen gas as the only side product. For many of the sugar substrates investigated, the distribution of regioisomers obtained is complementary to that of the traditional R(3)SiCl/base (base = pyridine, imidazole) methodology and gives convenient access to the 3,6- rather than the 2,6-silylated pyranosides, obtained as the main product by the silyl chloride method. The method also allows a selective axial silylation of levoglucosan and 1,3,5-O-methylidene-myo-inositol. In an attempt to rationalize the observed regioselectivities, ab initio predictions (HF/3-21G) have been made on the relative energies of some of the silylated products. They suggest that the observed regioselectivities do not reflect a kinetic vs thermodynamic product distribution but are induced by the silylation agent employed. Models for the possible origin of the observed regioselectivity in both silylation methods (silane- and silyl chloride-based) are discussed.
Subject(s)
Carbohydrates/chemistry , Hexoses/chemistry , Silanes/chemistry , Catalysis , Galactose/chemistry , Glucose/chemistry , Mannose/chemistry , Nanotechnology , Palladium/chemistry , Particle Size , Pentoses/chemistry , Pyrans/chemistry , Silanes/chemical synthesis , Substrate SpecificityABSTRACT
Pseudomonas aeruginosa PAO1 possesses two distinct lipopolysaccharide (LPS) O-polysaccharide species, A- and B-band LPS, the relative expression of which appears to be under environmental control. In an attempt to identify the influence these LPS types have on surface characteristics and adhesion, we examined the surface hydrophobicity and surface charge of P. aeruginosa PAO1 (O5 serotype) and its isogenic LPS derivatives which possessed A+B-, A-B+ and A-B- LPS. The surface characteristics of the strains affected their ability to adhere to hydrophilic (glass) and hydrophobic (polystyrene) surfaces. Cells possessing only A-band LPS demonstrated the highest surface hydrophobicity, followed by the strain lacking both A- and B-band LPS. The presence of B-band LPS resulted in a more hydrophilic surface. Strains lacking B-band LPS (A+B- and A-B-) had more electronegative surfaces than those possessing B-band LPS (A+B+ and A-B+), with cells lacking both A- and B-band LPS showing the highest surface electronegativity. These data suggest that the main surface-charge-determining groups reside in the core region of the LPS molecule. Cells with the lowest surface hydrophobicity and lowest surface charge (A+B+, A-B+) adhered to glass the most efficiently, implying a role for electrostatic interaction, whereas adhesion to polystyrene mirrored the relative hydrophobicities of the strains (A+B- > A-B- > A+B+ > A-B+). It is postulated that phenotypic variation in the relative expression of A- and B-band LPS may be a mechanism by which P. aeruginosa can alter its overall surface characteristics in such a way as to influence adhesion and favour survival.
