Bacterial Cell Inclusions and Endospores PDF

2-7: Bacterial Cells – Inclusions and endospores Lecture Overview: • Inclusions found within bacterial cells and the formation of endospores • Textbook: Chapter 2.7 / 2.8 Cell inclusions & microcompartments o Prokaryotic cells can contain “inclusions” - bodies or aggregates within the cell o Can...

2-7: Bacterial Cells – Inclusions and endospores Lecture Overview: • Inclusions found within bacterial cells and the formation of endospores • Textbook: Chapter 2.7 / 2.8 Cell inclusions & microcompartments o Prokaryotic cells can contain “inclusions” - bodies or aggregates within the cell o Can have diverse functions – often related to storage of a substance o Related, bacterial cells can also have “microcompartments” – protein shells than encase specific enzymes/metabolites/cofactors that carry out specific metabolism Carbon storage polymers • Bacteria (and other microbes!) store carbon when times are good, to be accessed during periods of starvation. • Diverse prokaryotes store carbon as lipids known as poly-β-hydroxyalkanoates (PHA), the most common of which is poly-βhydroxybutyric acid (PHB) • This polymer is produced when there is an excess of carbon/energy. It aggregates and forms large granules • Granules/polymers broken down for carbon/energy when needed PHA storage granules Textbook fig 2.20 Other storage granules o Similar storage granules are produced by select microbes that store other nutrients/molecules o Inorganic phosphate stored in polyphosphate granules (excess of phosphate). Broken down to produce nucleic acids/phospholipids, etc. o Sulfur storage granules produced by bacteria (and archaea) that oxidize reduced sulfur compounds for energy Polyphosphate (top) & sulfur (bot) storage granules Textbook fig 2.21 Gas vesicles o Some bacteria/archaea can float because they produce gas vesicles o Protein structures that keep water/solutes out, but allow gas in o Confer buoyancy – bring these microbes to a favourable environment o Example: cyanobacteria “blooms” at the surface of water – sunlight more intense, photosynthesis more efficient Floatation of a cyanobacterium due to gas vesicles in a freshwater lake Textbook fig 2.23 Microcompartments make challenging Some bacteria produce ↑ microcompartments – polyhedral protein shells that encase specific enzymes/metabolites/cofactors Chem more efficient Reactive (toxic) intermediate Carboxysomes – concentrate enzymes involved in carbon fixation – increases efficiency and reduces unwanted side reactions ↳Central part of Metabolism ↳ Do well Other microcompartments protect cell against toxic/reactive intermediates/biproducts Microcompartment used to protect against toxic intermediates produced during 1,2-propanediol degradation Frank et al., Journal of biotechnology, 2013 Endospores o Endospores are highly differentiated, dormant cells that can survive starvation and very harsh environmental conditions o Range of “spore” structures produced by different bacteria – but endospores only produced by certain members of the phylum Firmicutes (Gram positive). Much more resistant than other kinds of bacterial spores. o Endospores are extremely resistant to heat, radiation, drying, nutrient depletion, chemicals, and more! o Can survive for hundreds of years (or more) and then germinate and grow again!!! Wowzers! Endospores…kind of like cryogenically freezing yourself Endospores Textbook Fig 2.26 Vegetative cells (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 Endospore germination in B. subtilis Textbook Fig 2.26 Endospore features Metabolism/cell activities shut off Provide resistance/stability Textbook table 2.1 Creating a stable and resistant core Dehydration of the core is key - water goes from >80% to < 25% increases resistance to desiccation, heat, chemicals – 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 DPA structure 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 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 Textbook Fig 2.28 Major events in endospore formation Forespore contained within mother cell Textbook Fig 2.29