Course Contents: • Introduction to Microbiology • Functional Anatomy of Prokaryotic and Eukaryotic Cells • Microbial Metabolism • Carbohydrate Metabolism • Cellular Respiration • Fermentations • Lipid & Protein Catabolism • Microbial Photosynthesis • Microbial Growth • Control of Microbial Growth: Physical & Chemical Methods
Course Contents: • Classification of Microorganisms • Scientific Nomenclature • Phylogenetic Hierarchy • General Classification of Prokaryotes (Domains Bacteria & Archaea) and Viruses. • Viruses, Viroids and Prions • General characteristics of Viruses, Viral Structure, Viral Multiplication, Prions, Plant Viruses & Viroids. • Microbial Mechanisms of Pathogenicity • Portals of Entry • Penetration of Host Defenses • Transmission • Pathogenic Properties of Bacteria, Viruses, Fungi & Protozoa.
LECTURE 1: Prokaryotic Cell Structure and Function Microbiology and Virology; 3 Credit hours Atta-ur-Rahman School of Applied Biosciences (ASAB) National University of Sciences and Technology (NUST)
Cell types Eukaryotic Cell Prokaryotic Cell Animals, Plants, Fungi Bacteria & Archaea
Bacterial Cell Morphology, Arrangement Neisseria gonorrhoeae
Monstrous Microbes Thiomargaritanamibiensis Epulopisciumfishelsoni
Prokaryotic Cell Membrane Fluid Mosaic Model of Singer and Nicholson
Bacterial Cell Membrane • Lack sterols (steroid containing lipids) such as cholesterol • Many bacterial membranes contain sterol like molecules called hopanoids • Hopanoids are synthesized from the same precursors as steroids, and like the sterols in eucaryotic membranes, they probably stabilize the membrane.
Bacterial Cell Membrane It has been estimated that the total mass of hopanoids in sediments is around 1011–12 tons about as much as the total mass of organic carbon in all living organisms (1012 tons) and there is evidence that hopanoids have contributed significantly to the formation of petroleum.
Bacterial Cell Membrane • Lipid composition of bacterial membranes varies with environmental temperature in such a way that the membrane remains fluid during growth
Archaeal Membranes • They differ from both Bacteria and Eucaryain having branched chain hydrocarbons attached to glycerol by ether links rather than fatty acids connected by ester links
Archaeal Membranes • Sometimes two glycerol groups are linked to form an extremely long tetra-ether. • Usually the di-ether hydrocarbon chains are 20 carbons in length, and the tetra-ether chains are 40 carbons. • Cells can adjust the overall length of the tetra-ethers by cyclizing the chains to form penta-cyclic rings
Archaeal Membranes (a) A membrane composed of integral proteins and a bilayer of C20 di-ethers. (b) A rigid monolayer composed of integral proteins and C40 tetra-ethers
Inclusion Bodies • Inclusion bodies, granules of organic or inorganic material that often are clearly visible in a light microscope • Function: • These bodies usually are used for storage (e.g., carbon compounds, inorganic substances, and energy), and also reduce osmotic pressure by tying up molecules in particulate form.
Organic inclusion bodies • Glycogen • Glycogen is a polymer of glucose units composed of long chains formed by (1→4) glycosidic bonds and branching chains connected to them by (1→6) glycosidic bonds. • Poly-β-hydroxyalkanoates • Poly- β -hydroxy-butyrate (PHB) contains β hydroxybutyratemolecules joined by ester bonds between the carboxyl and hydroxyl groups of adjacent molecules.
Organic inclusion bodies Glycogen Glycogen Poly-β-hydroxyalkanoates
Organic inclusion bodies Poly-β-hydroxyalkanoates Glycogen
Organic inclusion bodies • Cyanophycingranules • are composed of large polypeptides containing approximately equal amounts of the amino acids arginine and aspartic acid. • Store extra nitrogen • Carboxysomes • are present in many cyanobacteria and other CO2fixing bacteria. • They are polyhedral, about 100 nm in diameter, and contain the enzyme ribulose-1, 5-bisphosphate carboxylase, called Rubisco. • Rubisco is the critical enzyme for CO2fixation, the process of converting CO2from the atmosphere into sugar.
Organic inclusion bodies • Gas vacuole • a structure that provides buoyancy to some aquatic prokaryotes. • Gas vacuoles are present in many photosynthetic bacteria and a few other aquatic procaryotes such as Halobacterium (a salt loving archaeon) and Thiothrix (a filamentous bacterium). • Gas vesicle walls are composed entirely of a single small protein. • These protein subunits assemble to form a rigid enclosed cylinder that is hollow and impermeable to water but freely permeable to atmospheric gases.
Organic inclusion bodies Gas Vesicles and Vacuolesin Anabaena flosaquaeclusters of the cigar shaped vesicles form gas vacuoles. Both longitudinal and cross sectional views of gas vesicles can be seen (arrows).
Inorganic Inclusion Bodies • Polyphosphate granules or volutin granules • is a linear polymer of orthophosphates joined by ester bonds. • Sulfur granules are used by some prokaryotes to store sulfur temporarily. • For example, photosynthetic bacteria can use hydrogen sulfide as a photosynthetic electron donor and accumulate the resulting sulfur in either the periplasmic space or in special cytoplasmic globules. • Magnetosome • Which is used by some bacteria to orient in the earth’s magnetic field
Inorganic Inclusion Bodies Chromatiumvinosum, a purple sulfur bacterium, with intracellular sulfur granules, bright-field microscopy Magnetotacticbacterium Aquaspirillummagnetotacticum the long chain of electron dense magnetite particles, MP.
The Nucleoid • The prokaryotic chromosome is located in an irregularly shaped region called the nucleoid. • Single circle of double stranded deoxyribonucleic acid (DNA) and some have a linear DNA chromosome • Vibrio choleraeand Borreliaburgdorferihave more than one chromosome • Chemical analysis of purified nucleoids reveals that they are composed of about 60% DNA, 30% RNA, and 10% protein by weight. • Condensing proteins instead of histones
The Nucleoid Chromosome released from a gently lysed E. coli cell
The Nucleoid • Membrane bound DNA containing regions are present in two genera of the unusual bacterial phylum Planctomycetes • Pirellula has a single membrane that surrounds a region, the pirellulosome, which contains a fibrillar nucleoid and ribosome like particles. • The nuclear body of Gemmataobscuriglobusis bounded by two membranes.
The Nucleoid An electron micrograph of Gemmataobscuriglobusshowing the nuclear body envelope (E), the intracytoplasmic membrane (ICM), and the paryphoplasm
Plasmids • Plasmids are small, double-stranded DNA molecules that can exist independently of the chromosome. • Both circular and linear plasmids • Different plasmids within a single specie • Borreliaburgdorfericarries 12 linear and 9 circular plasmids • The loss of a plasmid is called curing