Bacterial Sensing and Motility

Flashcards covering bacterial sensing, including two-component systems, second messengers, alternative sigma factors, sporulation, motility, chemotaxis, and twitching motility.

Sensor Kinase

Extracellular receptor for metabolite; intracellular communication pathway.

Response-Regulator Protein

Activated by sensor kinase; DNA binding protein.

Sensor Kinases

Located in cell membrane; acts as kinase and sometimes phosphatase; normally dimerizes to autophosphorylate itself at conserved histidine residue using ATP.

Response Regulators

Cytoplasmic; accepts phosphate from sensor kinase to conserved aspartate; can bind DNA to control transcription or proteins to control activity.

EnvZ/OmpR

Senses osmolarity changes; represses ompF and activates ompC.

ArcBA

O2 sensor; controls ~9% of genes in E. coli.

NtrBC

Response to N2 starvation; controls gene for importing or recycling N compounds.

Second Messengers

Small molecules produced in response to a signal.

cAMP

Cyclic AMP; involved in catabolite repression.

C-di-GMP

Cyclic dimeric GMP; controls motility, biofilm production, etc.

ppGpp

Guanosine tetraphosphate; controls stringent response.

Diguanylate cyclases

Synthesize c-di-GMP; contain GGDEF domain.

Phosphodiesterases

Destroy c-di-GMP; contain EAL domain.

Stringent Response

Amino acid starvation leads to decreased production of tRNA and rRNA to conserve energy and increased production of genes needed for biosynthesis of amino acids.

Empty tRNA enters A site

Sensed by RelA; RelA makes ppGpp using ATP and GDP.

ppGpp interacts with RNApol

Stops transcription of tRNA and rRNA genes; upregulates transcription of amino acid biosynthesis genes.

DksA + ppGpp

Destabilize open complex during transcription of downregulated genes and enhances open complex during transcription of upregulated genes.

Sigma Factor

Helps the core enzyme recognize the start of genes

σ70

General house keeping/ exponential growth

σS

Stress and stationary phase

σE

Restore membrane integrity and proper folding of membrane proteins

σH

Heat shock and other stress

σF (σ28)

Flagella synthesis

σ60

Nitrogen metabolism

FecI σ

Iron starvation

Spores

Spore- differentiated cells that are highly resistant to heat, radiation and chemicals and are metabolically dormant.

Exosporium

Thin covering surrounding the spore.

Spore coat

Thick layers of protein forming the spore coat.

Cortex

Beneath the coat; thick peptidoglycan.

Core

Contains high levels of dipicolinic acid and calcium; dehydrates spore resulting in gel-like consistency; stabilizes DNA with help from small acid-soluble DNA-binding proteins (SASPs); low pH.

Activation

Prepare spores for germination; often results from treatments like heating.

Germination

Environmental nutrients are detected; spore swelling and rupture of absorption of spore coat; increased metabolic activity.

Outgrowth

Emergence of vegetative cell.

Swimming Motility

Flagella based; cells swim through liquid.

Monotrichous

Single polar flagellum.

Amphitrichous

Single flagellum on each side.

Lophotrichous

Tuft of polar flagella.

Peritrichous

Many flagella around the body.

Filament

Extends from cell surface to the tip; hollow, rigid cylinder of flagellin protein.

Hook

Links filament to basal body.

Basal Body

Series of rings that drive flagellar motor.

Class I genes

transcriptional regulator for class II

Class II genes

make basal body, rod, and hook

Class III genes

include flagellin and motor proteins

4 rings in flagellar movement

Controls direction (C-ring), turns and anchors (MS ring), interacts with PG (P-ring), interacts with OM (L-ring).

Stator

Mot A and Mot B proteins; form channel through plasma membrane; protons move through channels using energy of proton motive force.

CCW Flagella

Flagella bundle; cell moves forward.

CW Flagella

Individual filaments unbundle; cells tumble; reorients the swimming direction.

Chemotaxis

The movement of a cell corresponding to a gradient of concentration of a substance

Methyl-accepting chemotaxis proteins (MCPs)

Chemoreceptors in membrane; binds environmental chemicals; initiates a series of interactions with cytoplasmic proteins that affects flagellar rotation.

CheA

Sensor Kinase in chemotaxis

CheY

Response Regulator in chemotaxis

Twitching motility

Pili based; On surfaces

Type IV pili

Made of PilA

PilQ

pore for pili assembly.