Cell Surface Structures

Question 1

Capsule

Answer 1

– Tightly packed matrix excluding small particles such as India ink
– Firmly attached to cell walls, some covalently bound peptidoglycan

Question 2

Slime layer

Answer 2

– Loosely packed matrix and more difficult to see
– Loosely attached and can be lost from cell surface

Question 3

Functions of outer surface layers

Answer 3

– These polysaccharides assist in attachment to solid surfaces
– Play a role in development and maintenance of biofilms
– Act as virulence factors in certain diseases
– Protects cells from destruction by phagocytic cells
– May also play a role in providing resistance to desiccation
– Food reserves

Question 4

Fimbriae

Answer 4

Attachment: Enable organism to stick to surfaces or form pellicles (thin sheets of cells on a liquid surface)
Common in pathogens

Question 5

Pilli

Answer 5

– Longer than fimbriae, only few per cell
– Functions are:
• Assist in surface attachment
• Conjugation: Facilitate genetic exchange between cells
• Cell motility: Type IV pilli involved in twitching
» Type IV pilli also important colonization factors for certain pathogens

Question 6

Cell inclusions

Answer 6

• Energy reserves and/ or carbon reserves of have special functions.
• Partitioned off in the cell by atypical membranes.
• Different cell inclusions: carbon storage, polyphosphate and sulfur, magnetic storage inclusions.
• These insoluble forms reduce the osmotic stress for the cells.

Question 7

Carbon storage polymers

Answer 7

• Poly-β-hyroxybutyric acid (PHB)
– Synthesized: excess of carbon
– Broken down: carbon skeleton during biosynthesis or to make ATP when needed
– Produced by both Bacteria and Archaea
• Glycogen
– Polymer of glucose
– Carbon and energy storage
– Produced when there is excess carbon in the environment and consumed when levels are limiting

Question 8

Cell inclusion types

Answer 8

Polyphosphate granules: inorganic phosphate
Sulfur granules: found in periplasm
Carbonate minerals: biomineralization by Cyanobacteria
Magnetosomes: impart magnetic dipole allowing megnetotaxis

Question 9

Gas vesicles

Answer 9

Gives buoyancy
Impermeable to solute and H2O
Gas permeable
E.g. Aquatic bacteria (Cyanobacteria)

Question 10

Endospores

Answer 10

• Dormant, metabolically inactive stage: produced by some bacteria during sporulation process [vegetative cell –> endospore in sporulating cell –>mature endospore –> germination into vegetative cell]
Resists: radiation, desiccation, nutrient depletion

Question 11

Sporulation cycle

Answer 11

– Asymmetric cell division
– Engulfment
– Cortex formation
– Synthesis of spore coat
– Maturation and lysis

Question 12

Endospore structure

Answer 12

Exosporium: outermost thin protein covering
Spore coat: layers of spore specific proteins
Cortex: cross linked peptidoglycan
Core:
– Consists of core wall, cytoplasmic membrane, cytoplasm, nucleoid,
ribosomes and other cellular essentials
– small acid soluble proteins (SASPs)
– Binds to DNA in the core and protects it from UV radiation, desiccation and dry heat
– Function as carbon and energy source during endospore germination
– Made up of Dipicolinic acid enriched in the core and is enriched with calcium: helps in dehydration and heat denaturation

Question 13

Endospore to vegetative cell

Answer 13

– Activation
• Heat spores for several minutes at high but sublethal temperatures
• Condition spores for germination in medium rich in specific nutrients e.g. amino acids
– Germination
• Lossofmicroscopicrefractility
• Increased ability to be stained
• Loss of resistance to heat and chemicals
– Out-growth
• Cells wells due to water uptake
• New RNA, protein and DNA are synthesized
• Endospores breaks to release the cell which then begins to grow