lecture 4 4.10 flagella and motility 4.11 gliding motility 4.12 bacterial responses: chemotaxis,...
TRANSCRIPT
Lecture 4
• 4.10 Flagella and Motility• 4.11 Gliding Motility• 4.12 Bacterial Responses: Chemotaxis,
Phototaxis, and other Taxes• 4.13 Bacterial Cell Surface Structures
and Cell Inclusions• 4.14 Gas Vesicles• 4.15 Endospores
Flagellar motion
• > 40 genes involved, include regulators
• movement driven by propeller-like rotation
• can propel cells up to 60 cell lengths/s
• equivalent of 2.5x faster than a cheetah!
• expensive process: must confer strong selective advantage
Motility in non-aqueous environments
1. polysaccharide “slime layer”— secreted slime used to pull cell along a
surface
2. special proteins in the outer membrane act like feet, which are activated by inner membrane proteins resulting in “crawling”
Cell structures and inclusions
• fimbriae - aid cell adherence to surfaces
• pili - conjugation, attachment to host cell
• glycocalyx - polysaccharide layer outside cell, attachment to host cells, protection from host immune system, resistance to dessication
• polyhydroxyalkanoate deposits - intracellular carbon and energy store
• polyphosphate - intracellular reserves
• elemental sulfur - intracellular granules
• magnetosomes - intracellular magnetite crystals (iron oxide)
• gas vesicles - cell buoyancy
Poly-3-hydroxybutyrate Poly-3-hydroxybutyrate (PHB)(PHB)
Carbon and energy reserveCarbon and energy reserve Accumulates intracellularly when carbon source is Accumulates intracellularly when carbon source is
not limiting for growthnot limiting for growth Can be utilized under carbon starvation conditionsCan be utilized under carbon starvation conditions Biodegradable bioplasticsBiodegradable bioplastics Production does not contribute greenhouse gases
CH3
—O·CH·CH2·C—
O[ ]n ~ 25,000
Endospores
Fig. 4.62Resistant to heat, radiation, acids, drying, chemicalsDo not contain RNADehydrated (only 10-30% H2O as vegetative cell)
Table 3.2 Differences between endospores andvegetative cells
Characteristic Vegetative cell Endospore
Microscopicappearance
Nonrefractile Refractile
Calcium content Low HighDipicolinic acid Low HighEnzymaticactivity
High Low
Metabolism (O2
uptake)Present Low or absent
Macromolecularsynthesis
Present Absent
mRNA Present Low or absentHeat resistance Low HighRadiationresistance
Low High
Resistance tochemicals andacids
Low High
Stainability bydyes
Stainable Stainable onlywith specialmethods
Action oflysozyme
Sensitive Resistant
Water content High, 80-90% Low, 10-25%Small acidsoluble proteins
Absent Present
Cytoplasmic pH ~7 5.5-6.0
How long can spores survive?
• See page 97, report that 250 million year old spores have been revived
• These spores were preserved in salt crystals of Permian age
• bacteria revived from brine deposits
• environmental contaminants prevented by steriliziation; controls for sterility
Endospore Formation
• triggered by sub-optimal growth conditions (heat, starvation, dessication, etc.)
• return to optimal conditions sees germination of spores within minutes
• studied by isolating mutants that do not form spores and studying at what point sporulation is blocked