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.

Prokaryotic Cell Structure and Function

LECTURE 1:

Microbiology and Virology; 3 Credit hours

Atta-ur-Rahman School of Applied Biosciences (ASAB)National University of Sciences and Technology (NUST)

Cell types

Prokaryotic Cell Eukaryotic Cell

Bacteria & Archaea

Animals, Plants, Fungi

Bacterial Cell Morphology, Arrangement

Neisseria gonorrhoeae

Shape, Arrangement & Size

Size of BacteriaBacteria Size

E. Coli 1.1 to 1.5 μm wide2.0 to 6.0 μm long

Mycoplasma 0.3μm appox. To Pox virus

Nano-bacteria 0.2 to 0.05 μm Smallest cell

Spirochaetes 500μm

Epulopiscium fishelsoni

600 to 80 μm

Thiomargarita namibiensis

750 to 100 μm

Smallest Eukaryotic cell;Nanochlorum

1 to 2 μm

Monstrous Microbes

Epulopiscium fishelsoni

Thiomargarita namibiensis

Prokaryotic Cell Organization

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 Eucarya in having branched chain hydrocarbons attached to glycerol by ether links rather than fatty acids connected by ester links

• 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

Archaeal Membranes

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

hydroxybutyrate molecules joined by ester bonds between the carboxyl and hydroxyl groups of adjacent molecules.

Organic inclusion bodiesGlycogen

Poly-β-hydroxyalkanoates

Glycogen

Organic inclusion bodies

Glycogen

Poly-β-hydroxyalkanoates

Organic inclusion bodies

• Cyanophycin granules– 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 CO2 fixing

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 CO2 fixation, the process of converting CO2 from 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 Vacuoles in Anabaena flosaquae clusters 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

Chromatium vinosum, a purple sulfur bacterium, with intracellular sulfur granules,

bright-field microscopyMagnetotactic bacterium Aquaspirillum

magnetotacticum 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 cholerae and Borrelia burgdorferi have 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 Gemmata obscuriglobus is bounded by two membranes.

The Nucleoid

An electron micrograph of Gemmata obscuriglobus showing 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• Borrelia burgdorferi carries 12 linear and 9

circular plasmids• The loss of a plasmid is called curing

Plasmids

Plasmids