Topic 2-L8 - Bacterial cells - Cell inclusions-endospores Flashcards
Prokaryotic cells can contain “inclusions” :
bodies or aggregates within the cell
Related, bacterial cells can also have “microcompartments” :
protein shells than encase specific enzymes/metabolites/cofactors that carry out specific metabolism
Diverse prokaryotes store carbon as lipids known as poly-β hydroxyalkanoates (PHA), the most common of which is
poly-β- hydroxybutyric acid (PHB)
PHA is a polymer that’s produced when
there is an excess of carbon/energy - aggregates and forms large granules
Inorganic phosphate in polyphosphate granules
(excess of phosphate – broken down to produce nucleic acids phospholipids)
Sulfur storage granules produced by bacteria (and archaea) that
oxidize reduced sulfur compounds for energy/CO2 fixation
Some bacteria/archaea can float because they produce
gas vesicles
gas vesicles functions
- keep water/solutes out and gas in
- bouncy : bring microbes to favourable environments
Example of gas vesicles in Bactria
Cyanobacteria
Some bacteria produce microcompartments –
polyhedral protein shells that encase specific enzymes/metabolites/cofactors
Carboxysomes (type of micro compartment) –
concentrate enzymes involved in carbon fixation – increases efficiency and reduces unwanted side reactions
Other microcompartments protect cell against
toxic/reactive intermediates/bi products
Endospores are highly differentiated,
dormant cells that can survive starvation and very harsh environmental conditions
endospores only produced by certain members of the
phylum Firmicutes (Bacillales, Clostridiales) – Gram positive.
- more resistant
Vegetative cells (endoscopes)
(normal, metabolically active, growing/dividing cells) differentiate into endospores upon nutrient deprivation
When the environment becomes more favorable, the spore can be
activated, germinate and return to the vegetative state
Creating a stable and resistant core
- dehydration of the core
- Dipicolinic acid (DPA)
- Small acid soluble proteins (SASPs)
Dehydration of the core is key -
increases dessication, heat, chemical resistance – inactivates (without denaturing) cell’s enzymes
Dipicolinic acid (DPA) – unique to spores. Is complexed with
Ca2+ (up to 10% of spore weight). Important for dehydration process, also binds/stabilizes DNA
Small acid soluble proteins (SASPs) only made during sporulation.
Bind DNA – help make it more compact, protect it from damage (UV, heat, denaturation, mutation). Also act as carbon/energy source during germination/outgrowth
Endospores - structure
- core
- cortex
- two membranes
- coat
Core is where
DNA/ribosomes are housed – will become the vegetative cell
Cortex
peptidoglycan layer
Two membranes
this “outer membrane” nothing like Gram negative OM – no LPS
Coat –
protective protein layer comprised of many different proteins
Some spores produce a second protein layer called the ___________
exosporium
Major events in Endospore formation
1) asymmetric cell division : commitment to sporulation septum formation
2) engulfment : (outer spore memb. Formed)
3) late sporulation: form coat and coat
4) maturation: dehydration of spore, Ca uptake
5) mother cell lysis
