1

Fig. 4.1

Bacterial Cell Structure

2

Cytoplasm

• dense gelatinous solution of sugars, amino acids, & salts

• 70-80% water

• serves as solvent for materials used in all cell functions

3

Chromosome

• single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell

• DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid

DNA temperature melting DNA temperature melting Bacteria classificationBacteria classification

4

A +T

G + C

5

plasmids

• small circular, double-stranded DNA• free or integrated into the chromosome• duplicated and passed on to offspring• not essential to bacterial growth & metabolism• may encode antibiotic resistance, tolerance to

toxic metals, enzymes & toxins• used in genetic engineering- readily manipulated

& transferred from cell to cell

6

Ribosomes• made of 60% ribosomal RNA & 40%

protein

• consist of 2 subunits: large & small

• procaryotic differ from eucaryotic ribosomes in size & number of proteins

• site of protein synthesis

• All cells have ribosomes.

7

8

Inclusions, granules

• intracellular storage bodies

• vary in size, number & content

• bacterial cell can use them when environmental sources are depleted

• Examples: glycogen, poly--hydroxybutyrate, gas vesicles for floating, sulfur and polyphosphate granules

9

10Fig 4.10

11

Cytoplasmic membrane Cytoplasmic membrane ProtoplastProtoplast

SpheroplastSpheroplast L formsL forms

12

4 groups based on cell wall 4 groups based on cell wall compositioncomposition

1. Gram positive cells

2. Gram negative cells

3. Bacteria without cell walls

4. Bacteria with chemically unique cell walls

13

Gram positiveGram positive

Gram negativeGram negative

14

Gram positive Gram negative

Fig 4.16

15

Lipopolysaccharide

Lipid A• Glucosamine disaccharide

• Beta hydroxy fatty acids

Core • Heptoses• Ketodeoxyoctonic acid

O-antigenHighly variablen

(Hydroxy myritic Acid)

LPS functionLPS functionEndotoxinsEndotoxinsExotoxinsExotoxins

16

17

Gram positive wall

18

Gram negative cell wall

19

Peptidoglycan

20

CytoplasmCytoplasm

CytoplasmCytoplasm

Lipoteichoic acid Peptidoglycan-teichoic acid

Cytoplasmic membrane

Inner (cytoplasmic) membrane

Outer Membrane

LipopolysaccharidePorin

lipoprotein

Peri

plas

mic

spa

ce

21

r r rrr

r

Gram Positive Cell EnvelopeGram Positive Cell Envelope

CytoplasmCytoplasm

rrrr

Lipoteichoic acid

Peptidoglycan-teichoic acid

Cytoplasmic membrane

22

Glycocalyx

• Coating of molecules external to the cell wall, made of sugars and/or proteins

• 2 types1. capsule - highly organized, tightly attached2. slime layer - loosely organized and attached

• Functions– attachment– inhibits killing by white blood cells– Receptor (K antigen)

23

2 Types of Glycocalyx

24

Biofilms

25

FlagellaFlagella

26

lophotrichous

Monotrichous

amphitrichous peritrichous

27Fig 4.2b

28

Fimbrae

• Adhesion to other cells and surfaces

29

pili

• rigid tubular structure made of pilin protein

• found only in Gram negative cells

• Functions – joins bacterial cells for DNA transfer (conjugation)– adhesion

30

Conjugation

31

endospores

Important components in endospore:

CalciumCalciumDipicolinic AcidDipicolinic Acid

32

SporulationSporulation

The endosporeThe endospore

34

35

36

Major Taxonomic Groups of Major Taxonomic Groups of BacteriaBacteria

• Gracilicutes – gram-negative cell walls, thin-skinned

• Firmicutes – gram-positive cell walls, thick skinned

• Tenericutes – lack a cell wall & are soft• Mendosicutes – archaea, primitive

procaryotes with unusual cell walls & nutritional habits

Grwth in BacteriaGrwth in Bacteria

• Temperature

• Nutrients

• pH

• Osmotic pressure

37

38

• Minimum temperature – lowest temperature that permits a microbe’s growth and metabolism

• Maximum temperature – highest temperature that permits a microbe’s growth and metabolism

• Optimum temperature – promotes the fastest rate of growth and metabolism

TemperatureTemperature

39

3 temperature adaptation groups

Bacterial MetabolismBacterial Metabolism

• Phototropho Photoautotroph (Photolitotroph)o Photoheterotroph (Photoorganotroph)

• Chemotropho Chemoautotroph (Chemolitotropho Chemoheterotroph (Chemoorganotroph)

40

Stages of metabolism in Stages of metabolism in chemoheterotrophic bacteriachemoheterotrophic bacteria

• Digestion

• Absorption (Passive and active transportation)

• Preparation for oxidation

• Oxidation

41

42

Oxygen requirements

43

44

Fermentation

• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

• Uses organic compounds as terminal electron acceptors

• Yields a small amount of ATP• Production of ethyl alcohol by yeasts acting on

glucose• Formation of acid, gas & other products by the

action of various bacteria on pyruvic acid

45

Fermentation

46

Binary divisionBinary division

Growth Curve

Con

tinuo

us C

ultu

re, C

hem

osta

t

Chemostats are a means of keeping a culture in log phase indefinitely.

49

Methods in bacterial identification

1. Microscopic morphology2. Macroscopic morphology – colony appearance3. Physiological / biochemical characteristics4. Chemical analysis5. Serological analysis6. Genetic & molecular analysis

• G + C base composition• DNA analysis using genetic probes• Nucleic acid sequencing & rRNA analysis

Bacterial Colonies

• Standard Bacterial Count

• Colony-Forming Units

• Plaque-Forming Units

•Spread Plate

• Pour Plate

• Soft-Agar Overlay

Solid Medium

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53