080506 Möllby

1

Modern concepts about bacterial cell

E-content for Programme: B.Sc.Botany (modern concept about bacterial

cell)

Prepared by Prof. Kanchan kumari ,

Department of Botany

S.U College, Hilsa

Patliputra university

email-kanchanancbio@gmail.com

080506 Möllby

2

Approximate timing of major events in the history of life on Earth.

080506 Möllby

3

080506 Möllby

4

ProcaryoteEucaryote

080506 Möllby

5

Composite Bacterial Cell

080506 Möllby

6

BACTERIAL DNA

• One circular chromosome packed to ”nucleoid”

• Plasmids: smaller circular DNA structures

• Genome size: 0.5 to 6 Mb (500 to 6000 genes)

- extrachromosomal DNA

- multiple copy number- genes for antibiotic-resistance- genes encoding toxins- multiply independently of cell division

080506 Möllby

7

Cytoplasmic membrane

• Lipid bilayer • Semipermeable barrier• No sterols

Contains:• Structural proteins• Transport proteins• Electron transport system• Enzymes• Ion pumps• Flagellum anchor

080506 Möllby

8

CYTOPLASM

Cell wall• rigid, protecting cell from osmotic lysis

• made up of PEPTIDOGLYCAN

Cell membrane

Bacteria have no inner cytoskeletonCell wall = outer skeleton

080506 Möllby

9

NAG NAM

Basic components of peptidoglycan

080506 Möllby

10

Structure of peptidoglycan

G = NAGM = NAM

080506 Möllby

11

All bacteria have aPEPTIDOGLYCAN cell wall

Cell envelopes are different

basis for stain reaction developed byChristian Gram, 1884

BUT

*

*Exception: genus Mycoplasma

Gram positive G+Gram negative G-

080506 Möllby

12

Gram positive cell wall

080506 Möllby

13

TEICHOIC ACIDPolymer of phosphorylated sugar alcohols/glycerol

Ribitol based

Glycerol based

LIPOTEICHOIC ACIDfatty acid anchorin cell membrane

080506 Möllby

14

Fluid Mosaic model (by Singer and Nicholson) of bacterial membrane structure

(under EM) Most of these proteins have one or more trans membrane (TM) segments,

and they interact closely with nearby lipids as well as other proteins. In addition, there

are peripheral membrane proteins that associate at the surface of the membrane and

lipid anchored proteins that are held into the membrane by covalently attached fatty

acids or lipids. hydrophilic moieties are always on the portions of glycoproteins and

glycolipids external to the membrane bilayer.

Like

hopanoids

Hydrophobic

-helix

080506 Möllby

15

Gram negative cell wall

Lipopolysaccharide

Outer membrane

Periplasmic space

Cytoplasmic membrane

Cytoplasm

Peptidoglycan

Porin proteins

080506 Möllby

16

Lipopolysaccharide = endotoxin

O-antigen

Core poly-saccharide

Lipid A isanchored inouter mem-brane (OM)

080506 Möllby

17

IMPLICATIONS OF GRAM REACTION

• Diagnostically useful

• LPS in G- and TA in G+ activate complement &

are important for pathogenicity

• Sensitivity to antibiotics, lysozyme, complement

080506 Möllby

18

Flagella and Motility

• Size-20 nm across and up to 15 to 20m long.

• Monotrichous-single and located at one end

• Amphitrichous- single flagellumat each pole

• Lophotricous-cluster of flagella at one or both ends

• Peritrichous-spread over the whole surface

• Flagella can rotate at rates as fast as 40 to 60 revolutions per second.

080506 Möllby

19

Pseudomonas Proteus

Escherichia coli

080506 Möllby

20

Flagella and Motility

• The mechanism of flagellar movement appears to be rotation; the hook and helical structure of the flagellum causes the flagellum to act as a propeller, thus driving the bacterium through its watery environment

• Counterclockwise rotation causes forward motion (called a run)

• Clockwise rotation disrupts forward motion (resulting in a tumble)

080506 Möllby

21

FLAGELLA = locomotory organelles• project as long strand(s) from bacterial surface• embedded in cytoplasmic membrane• flagellin (protein) subunits• hollow tubular structure•move bacteria by propeller like action

Outer membrane

Peptidoglycan

Cytoplasmic membrane

THE FLAGELLUM ROTATOR MACHINE

M ringS ring

Hook filament

P-ring

L-ring

080506 Möllby

22

Chemotaxis

• Chemotaxis is directed movement of bacteria either towards a chemical attractant or away from a chemical repellent

• The concentrations of these attractants and repellents are detected by chemoreceptors in the surfaces of the bacteria

• Directional travel toward a chemoattractant (biased random walk toward attractant) is caused by lowering the frequency of tumbles (twiddles), thereby lengthening the runs when traveling up the gradient, but allowing tumbling to occur at normal frequency when traveling down the gradient

• Directional travel away from a chemorepellent (biased random walk away from repellent) involves similar but opposite responses

• The mechanism of control of tumbles and runs is complex, involving numerous proteins and several mechanisms (conformation changes, methylation, and phosphorylation) to modulate their activity;

• despite this complexity chemotaxis is fast, with responses occurring in as little as 200 meters/second

080506 Möllby

23

AXIAL FILAMENTS

• spirochetes, e.g., Treponema pallidum• similar function to flagella• run lengthwise along the cell• snake-like movement

080506 Möllby

24

Pili = Fimbriae

• Short hair-like projections

• Aid in adhesion to host epithelium (e.g. cornea)

• Special (longer) F-pili for conjugation

080506 Möllby

25

CAPSULE AND SLIME LAYER

• outside cell envelope

• ”capsule” well defined

• ”slime layer” or ”glycocalyx” not so defined

• usually polysaccharides

• often lost in vitro

• protective in vivo (important virulence factor)

080506 Möllby

26

Encapsulated bacteria are less well phagocytosed

080506 Möllby

27

BACTERIAL CELL DIVISION

Binary fission

• Chromosome attaches to membrane• DNA is replicated• Cell membrane + envelope invaginate• Daughter cells separate

NOTE:Plasmids replicate independently

080506 Möllby

28

BACTERIAL ENDOSPORE

080506 Möllby

29

BACTERIAL METABOLISM IN RELATION TO OXYGEN

Aerobic

Anaerobic

Facultative

Microaerophilic

Obligate aerobes require molecular oxygen

Obligate (strict) anaerobes can not grow in presence of oxygen

Facultative anaerobes grow both with and without oxygen (most bacteria)

Prefer reduced amount of oxygen

080506 Möllby

30

SPORE FORMATION

Triggered at adverse conditions, such as lack of nutrients,dryness, heat, etc.

15% of the spore’s dry

weight consists of dipicolinic

acid complexed with

calcium ions. Calcium

dipicolinate stabilizes DNA

at high temperature

080506 Möllby

31

WHAT IS A BACTERIAL SPORE?

•Dormant state designed for long-term survival

• Contains the whole genome

• Germinates when life

looks better again

•Contains calcium bound to dipicolinic acid

080506 Möllby

32

ENDOSPORE CYCLE

Bacillus & Clostridium

Bacterial spores are NOT for

multiplication

To kill spores: autoclave 120°C, 20 min

Septum

formation

Lysis of sporangium

Germination of

endospore

080506 Möllby

33

080506 Möllby

34

CLASSIFICATION OF BACTERIA

Kingdom Monera MoneraPhylum

Class

Order Eubacteriales Eubacteriales

Family Enterobacteriaceae Micrococcaceae

Genus Escherichia Staphylococcus

Species coli aureus

Type O157:H7 MRSA

080506 Möllby

35

Binomial Nomenclature

Genussuggestive of morphology, discoverer, other characteristics(Streptococcus, Staphylococcus, Neisseria, Escherichia, Mycobacterium)

speciessuggestive of metabolic features, biochemical characteristics, disease(pyogenes, aureus, gonorrhoeae, coli, tuberculosis, anthracis)

More examples:Bordetella pertussis, Yersinia pestis, Haemophilus influenzaeLegionella pneumophila etc etc

080506 Möllby

36

Helicobacter Pseudomonas

Staphylococcus Borrelia

080506 Möllby

37

BACTERIA

• Variable morphology• Single circular chromosome• Unique type of cell wall

•Size 1-5 mmCoccus

Spiral

080506 Möllby

38

Bacillus anthracis

080506 Möllby

39

Staphylococcus aureus