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.

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

The Flagellum

1000 H+ / rotation

> 40 genes involved

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

Steps in Biosynthesis of Flagella

Run

Types of Flagellar Arrangements

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”

Absence of chemical attractant

Fig. 4.46a

Presence of chemical attractant

Fig. 4.46b chemical gradient sensed in a temporal manner

Measuring Chemotaxis

control repellent

attractant

Other types of taxes

• phototaxis - light

• aerotaxis - oxygen

• osmotaxis - osmotic strength

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-ß-hydroxybutyrate (PHB)

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

Gas Vesicle Proteins

Fig. 4.58

watertight, gas-permeable structure(hydrophobic proteins)

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

Dipicolinic acid

Fig. 4.61Characteristic of endospores

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

Sporulation

Initiated when nutrients limiting

Stages determined by mutational analysis

~200 genes involved

SASP = small acid-soluble spore proteinsCortex is composed of peptidoglycanExosporium is a thin protein covering

8 h for entire process