Lecture 4: Cell Surface structure, motility, and endospores

External surface layers of prokaryotic structures

Glycocalyx; slime layer, capsule

S-layer

Glycocalyx

network of polysaccharides with a slimy/gummy texture

Not structural

Types of glycocalyx

slime layer and capsule

Slime layer

diffuse, unorganized, and thin

loosely attaches and is easily removable

gliding mobility

Gliding mobility

smooth translocation of cells over a surface by an active process (E)

The pili extend, attach, and retract to pull the cell forward

The slime layer helps propel the cell forward by

decreasing frictionC

Capsule

well organized, firmly attached, and not easily removed

Capsules features

resist phagocytosis and desiccation

formation of biofilm

Phagocytosis

engulfed by another cell

ex: WBC or protozoans

Desiccation

drying out

the polysaccharide is hydrophilic thus retains water

Biofilm

complex, polysaccharide-enclosed communities

require a surface to attach to

Where do biofilms grow?

anywhere there is moisture, nutrients, and a surface

Hospital-Acquired infections (HAI)

resistant to antibiotics, are very costly

Streptococcus mutans

leading cause of tooth decay

glucose undergoes glucosyltransferase to make dextran

Dextran

forms capsules that adhere to enamel and form plaques that produce acids that lead to tooth decay

S-layer are made of

protein or glycoproteins in a regular geometric pattern

S-layer functions

selective sieve

protection

adhesions

S-layer protects against

enzymes, phagocytosis, bdellovibrio

pili and fimbriae are made of

pilin

Functions of pili and fimbriae

adhesions

overcome electrostatic repulsion

conjugation

Pili/fimbriae adhesion

allows prokaryotes to colonize surfaces

Pili/fimbriae overcome electrostatic repulsion

binding to host without being close

pilling depolymerized, decreasing the distance between cells and allowing for adhesins to make contact

Pili/fimbriae Conjugation

transfer of DNA from one bacterium to another

enables genetic recombination (evolution, genetic diversity)

Flagella

locomotion, attachment, virulence factor

Polar monotrichous flagellum

single pole at one end

Polar amphitrichous flagellum

single pole at each end

Lophotrichous flagellum

tuff/multiple at one or both poles

Peritrichous flagellum

all over the surface

Flagella main parts

filament

hook

basal body

Filament

rigid, helical

extends from surfaces F

Filament synthesis

flagellin subunits produced in the cytoplasm are transported through the hollow tube and attached to the growing tip in helical chains

Hook

at base allows for flexible coupling

Basal body

most complex component

L ring, P ring, MS ring, C ring, Central rod

L ring

anchored in OM

P ring

Anchored in PG

MS ring

In PM

C ring

cytoplasmic side of the MS ring

Central rod

goes through the rings

In gram-pos bacterium there are ___ rings

2, outer and inner

Flagellum function

motor rotates rapidly

flagellum rotates, propelling bacterium through fluid

Mot A and Mot B proteins

forms a channel where PMF occurs

gives energy for the flagellum to rotate

Fil proteins

helps with direction of rotation

Taxis

directed movement in response to stimulus

Functions of taxis

towards resources, away from unfavorable conditions

wants to increase survival and reproduction

Taxis are attracted to ____ and repelled from

nutrients

toxin and waste products

Positive response

towards stimulus

Negative response

away from stimulus

Types of responses

chemotaxis, phototaxis, osmotaxis, aerotaxis, thermotaxis

Chemotaxis in e.coli

response to chemical gradient

2 types of swimming behavior

Runs and tumbles

Runs

smooth forward motions in a straight line

Tumbles

cell stops and jiggles

interrupts runs to allows a new direction in the next run

Directions of flagellar rotation of monotrichous

runs:

tumbles:

counter clock wise

clockwise

Directions of flagellar rotation of peritrichous

runs:

tumbles:

bundles and counter clock wise

unbundles and clockwise

Biased random walk

movement in one direction tends to be prolonged

In bias random walks if there is high [attractant] or low [repellent]

the bacterium tumbles less frequently and has longer runs as both cIn bias random walks if there is high [attractant] or low [repellent]onditions are favorable

In bias random walks if there is low [attractant] or high [repellent]

bacterium tumbles as a normal rate as both are harmful

tumbles for a higher chance of reorienting in a “better” direction

The net movement of flagellum is always towards a ...

optimal environment

Endospores

produced by certain gram-pos

not a reproductive structure

resistant, dormant survival form

Structure of endospore internal to external

coat

germ cell wall

core

cortex

inner membrane

exosporium

outer membrane

core - inner membrane - germ cell wall - cortex - outer membrane - coat - exosporium

core

nucleoid, ribosome, etc

inner membrane

phospholipid bilayer

germ cell

PG

cortex

PG

outer membrane

phospholipid bilayer

Coat

multi-layered, highly crossed-linked, multiple proteins

Exosporium

glycoproteins

Phospholipid bilayers restrict the passage for

hydrophilic and charged molecules

Endospores are highly resistant to

antibodies, most disinfectants, physical agents(radiation, boiling, and drying)

Endospores can survive up to ____ and can be killed by

1000 years, autoclave (high steam pressure)

Endospores are highly resistant because of

calcium-dipicolinate in core

small acid-soluble spore proteins

dehydration of core

DNA repair enzymes

Calcium-dipicolinate in core

inserts between DNA bases and protects endospores from heat

Small acid-soluble spore protein

binds to DNA, protects for UV, desiccation, and heat

Dehydration of core

less water than cytoplasm as water can be destructive

DNA repair enzymes

function during germination

Germination

triggered by detection of sugars and AA

transforms into vegetative cell (living normally)

Sporulation

forming of endospore

triggered by nutrient limitation