The Microbial World

Tree of Life

• Phylogeny based on 16S ribosomal DNA.

• Three domains of living organisms

• Borderline entities– Viruses

– Viroids

– Prions

Characteristics of Living Organisms

• Metabolism

• Growth

• Reproduction

Characteristics of Cells

• Cell membrane separates cell from outside

• DNA as genetic material

• Ribosomes

• Basic structural macromolecules

• Regulate flow of materials in and out

• Reproduce and are the result of reproduction

• Require energy

Types of Cells

• Prokaryotes

• Eukaryotes

Generally eukaryotic cells are morphologically complex and biochemically simple; prokaryotic cells are morphologically simple and biochemically complex

Prokaryotic Cell (Minimal)

• No “true” nucleus

• No internal membrane bound organelles

Prokaryotic Cell (Maximal)

• Inclusions• External

structures for attachment, genetic exchange, and movement

Prokaryotic Cell Wall

• Unique chemical composition

• Protects cell from osmotic lysis

• Two major types– Gram positive– Gram negative

Gram Negative Cell Walls

Gram Positive Cell Walls

Structures Exterior to the Wall

Glycocalyx/Capsule

• Extracellular polymer

• Important in attachment to surfaces - biofilms

• Protects against phagocytosis

Biofilm Formation

Pili

• Short hairlike appendages projecting from the bacterial cell surface

• Composed of protein• Function:

– Attachment

– Transfer of DNA

Flagella

• Long protein (flagellin) appendage

• Motility• Structure and function

like a propeller• Arrangement of flagella

sometimes used in taxonomy/identification of bacteria

Cell Membrane

• Fluid Mosaic Model

• Phospholipid bilayer with embedded proteins

• Regulates transport of substances into and out of the cell

Membrane Transport

• Diffusion

• Passive/Facilitated Transport

• Group Translocation

• Active Transport

Internal Structures

Nucleoid• Bacterial chromosome• Single circular piece of DNA• No associated histones

Plasmids• Extrachromosomal small piece of DNA

• Independent of chromosome

• Code of ancillary functions– Antibiotic resistance– Metal resistance– Catabolic pathways

• Self-replicating

• Used in genetic engineering

Ribosomes• Combinations of protein and RNA

• Essential structures

• Function– Protein synthesis– Expression of genetic information

• Size differs between prokaryotes and eukaryotes

• Prokaryotes: 70S

Inclusions

• Magnetosomes• Poly-hydroxybutyrate• Sulfur granules• Glycogen• Polyphosphate granules