Recognized by innate immune system; responsible for causing endotoxic shock.
Core Oligosaccharide: Contains sugars like ketodeoxyoctonate (KDO), heptoses, glucose, galactose, and N-acetyl glucosamine.
O-Antigen:
Composed of repeating oligosaccharide units, highly variable in structure.
Importance of Lipid A
Acts as an endotoxin recognized by Toll Like Receptor-4 in the immune system.
Triggers an inflammatory response which may lead to endotoxic shock – causing multi-organ failure.
Estimated 200,000 deaths per year in the US due to endotoxins.
Archaeal Cell Envelope
Characteristics:
Single membrane composed of monolayers of tetra-ether lipids, not bilayers, making it impermeable to protons.
S-layer made of protein layers can resist extreme environmental conditions (e.g., in extremophiles like Sulfolobus solfataricus).
Pseudomurein:
Found in some Archaea (like methanogens) but lacks peptidoglycan.
Contains N-acetylglucosamine and N-acetyltalosaminuronic acid linked by β,1-3 glycosidic linkages (resistant to lysozyme).
Surface or S-Layers
Present in most Archaea and some bacteria, composed of a paracrystalline arrangement of glycoprotein that forms a protective and porous structure.
Flagella
Functionality:
Confers movement and allows bacteria to swim via rotational movement (CW and CCW) powered by an ion-driven rotary motor.
Flagella arrangements can vary: monotrichous, lophotrichous, amphitrichous, and peritrichous.
Flagella Structure
Components:
Basal body (the motor), filament (the propellor), hook (connecting basal body and filament).
Proton movement in the flagellar motor can involve up to 1000 protons per rotation for Gram-negative bacteria.
Chemotaxis
Bacteria can move towards or away from chemical gradients (e.g., nutrients or repellents).
In peritrichous flagella (e.g., E. coli):
Counterclockwise rotation results in runs, while clockwise rotation leads to tumbles.
Runs can be extended or shortened based on environmental signals, facilitating a biased random walk.
Fimbriae and Pili
Fimbriae:
Thin, filamentous structures that help bacteria adhere to surfaces via adhesins at their tips.
Commonly peritrichous, important for forming biofilms.
Pili:
Similar structure to fimbriae but typically less in number and longer. Important for genetic exchange (conjugation) and motility (type IV pili).
Clinical Significance: Fimbriae and pili mediate adherence in pathogens, crucial in infections (e.g., E. coli, Neisseria gonorrhoeae).
E. coli P-Type or Type 1 Pili
Structure:
Composed of structural subunits (Pap A) and adhesins (Pap G) that bind to host epithelial cells, significant in urinary tract infections.
Summary of Bacterial Surface Structures
Bacterial surface structures play crucial roles in pathogenicity, environmental resistance, and motility. The structural variability and functional diversity among Gram-negative bacteria and Archaea illustrate adaptations to diverse habitats and interactions with host organisms.