Bacteria and Archaea 24-09-2024 PDF

Bacteria and Archaea 24-09-2024 Three Domains of Life Bacteria The average size of a bacterium is between 1 and 10 micrometers long and 0.2 to 1 micrometer in width The smallest bacteria, like Mycoplasma genitalium, measure 200-300 nm. The largest bacteria, like Thiomargarita nam...

Bacteria and Archaea 24-09-2024 Three Domains of Life Bacteria The average size of a bacterium is between 1 and 10 micrometers long and 0.2 to 1 micrometer in width The smallest bacteria, like Mycoplasma genitalium, measure 200-300 nm. The largest bacteria, like Thiomargarita namibiensis, can be up to 750 micrometers in size.  Bacterial Cell Structure Cell Envelope Plasma Membrane, Cell wall, Capsule (optional) Surface Appendages Flagella Pili Fimbriae Cytoplasm Ribosomes Mesosomes Nucleoid Plasmids (optional)  Bacterial Cell Structure Cell Envelope Plasma Membrane, Cell wall, Capsule (optional) Surface Appendages Flagella Pili Fimbriae Cytoplasm Ribosomes Mesosomes Nucleoid Plasmids (optional)  Bacterial Cell Envelope Cell Wall Gram positive Gram negative  Bacterial Cell Envelope N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) Meso-diaminopimelic acid (mDAP) N-acetylmuramic acid (NAM) L-alanine ligase-MurC  Functions of Bacterial cell wall Provides structural support and maintains the bacterium's shape. Protects the cell from osmotic pressure and lysis. Acts as a barrier against harmful substances and immune responses. Aids in bacterial attachment and colonization of surfaces. Plays a role in cell division and regulates permeability.  Various strategies to target the bacterial cell wall Strategy Mechanism Examples Targeted Bacteria Hydrolyzes glycosidic Broad spectrum bonds in Natural antimicrobial Lysozyme (effective against peptidoglycan, enzyme many bacteria) leading to cell lysis Cleaves - Found in Lytic peptidoglycan chains bacteriophages Gram-positive and Transglycosylase and facilitates cell - Some bacterial Gram-negative wall remodeling species Inhibits - Penicillins (e.g., transpeptidases, Amoxicillin) Primarily Gram- β-lactam Antibiotics preventing cross- positive and some - Cephalosporins linking of Gram-negative (e.g., Ceftriaxone) peptidoglycan Removes terminal D- alanine residues, - Class B β- Gram-positive Carboxypeptidase influencing lactamases bacteria peptidoglycan structure Cleaves peptide bonds within Various bacteria, - Found in some Endopeptidase peptidoglycan layers, especially Gram- bacteria leading to positive destabilization Hydrolyzes amide bonds in - Various bacterial Primarily Gram- Amidase peptidoglycan, amidases positive bacteria contributing to cell wall turnover  Cell Membrane/Plasma Membrane Structure Phospholipid bilayer: 5-10 nm, Composed of hydrophilic heads and hydrophobic tails, forming a semi-permeable membrane. Proteins: Porins, ABC transporters, receptor proteins, structural proteins Hopanoids: Some bacteria contain hopanoids that stabilize the membrane, similar to cholesterol in eukaryotes. Functions Regulates the entry of nutrients and exit of waste. Facilitates passive (diffusion) and active transport (requiring energy). Membrane proteins act as receptors, responding to environmental signals. Involved in cellular respiration and ATP synthesis in some bacteria. Plays a role in cell growth and formation of new cell walls. Gram Staining  Gram-Positive Bacteria Gram-Negative Bacteria Thick peptidoglycan layer (20–80 nm), retains crystal violet, Thin peptidoglycan layer (2–7 nm), loses crystal violet, stains purple in Gram staining. stains pink/red in Gram staining. Teichoic acids, Lipoteichoic acid (LTA) present, provide No teichoic acids, but lipopolysaccharides (LPS) present, structural support and ion regulation. contributing to strong immune responses. Outer membrane present, acts as a barrier to antibiotics and No outer membrane, peptidoglycan is the outermost layer. harmful agents. Defined periplasmic space between outer and inner Narrow periplasmic space or absent. membranes, containing enzymes for defense. More susceptible to antibiotics like penicillin and Less susceptible to many antibiotics due to the outer vancomycin. membrane barrier. LPS and porins present, with porins aiding in selective No LPS or porins in the cell wall. transport. More resistant to chemical attacks but sensitive to More resistant to desiccation due to thick peptidoglycan. desiccation. Examples: Staphylococcus aureus, Bacillus. Examples: E. coli, Salmonella, Pseudomonas.  Capsules Capsule Composition Polysaccharides Homopolysaccharides: Made of one type of sugar (e.g., dextran). Heteropolysaccharides: Composed of multiple sugar types (e.g., hyaluronic acid). Polypeptides: Some capsules, like those in Bacillus anthracis, consist mainly of poly-D-glutamic acid. Glycoproteins: Capsules may include both protein and carbohydrate components. Function The polysaccharide nature can help bacteria avoid recognition by immune cells (evading immune system). The capsule enhances adhesion to surfaces and host tissues, promoting colonization and biofilm formation. Capsules help protect bacteria from desiccation and Crystal violet +India ink or nigrosin or congo red antimicrobial agents.