Bacterial Physiology and

Genetics

Understand the meaning of the growth.

Important factors for growth.How genetic variation occur in

bacteria?

Meaning of Bacterial physiology ?

The biochemical reactions that together enable bacteria to live, grow and reproduce.

Microbial Growth

Microbial Growth - refers to the number of cells

Requirements for Growth• Physical• Chemical

Nutritional Requirements

Physical Requirements

Autotrophs Heterotrophs

Organic and Inorganic substances

Physical Requirements

Temperature• psychrophiles (cold loving microbes )

• range 00 C - 200 C

• mesophiles (moderate temp. loving microbes)• range 250 C - 400 C

• thermophiles (heat loving microbes)• range 550C - 880 C

pH

Most bacteria grow between pH 7.2 - pH 7.4

Very few can grow at below pH 5• many foods, like cheeses are preserved from spoilage

by acids produced during fermentation

Oxygen

Bacteria can be classified base on their oxygen requirements

1. Obligate Aerobes

2. Obligate Anaerobes

3. Facultative Aerobes

Facultative Anaerobes

4. Microaerophilic

Oxygen is lethal to some organisms All organisms produce superoxide ( O2-)

Superoxide is toxic to cells Superoxide must be neutralized

Superoxide dismutase

O2- + O2- + 2 H+ -------> H2O2 + O2

Hydrogen peroxide is also toxic to cells and it must be neutralized

Catalase

2 H2O2 --------> 2 H2O + O2

Obligate Anaerobes lack:• Superoxide dismutase ( SOD )• Catalase

Phases of Growth

4 Phases

1. Lag Phase 2. Log Phase 3. Stationary Phase 4. Death Phase

1. Lag Phase

Bacteria are first introduced into an environment or media

Bacteria are “checking out” their surroundings

cells are very active metabolically # of cells changes very little

2. Log Phase

Rapid cell growth (exponential growth) population doubles every generation microbes are sensitive to adverse conditions

• antibiotics

3. Stationary Phase Death rate = rate of reproduction cells begin to encounter environmental

stress• lack of nutrients• lack of water• not enough space• metabolic wastes• oxygen• pH

Endospores would form now

4. Death Phase

Death rate > rate of reproduction Due to limiting factors in the environment

Bacterial Growth - increase in the # of cells

Binary Fission

Generation Time (Doubling Time)• time required for a cell to divide• most about 1 Hr. To 3 Hrs.

• E. coli - 20 minutes

• Mycobacterium tuberculosis - 24 Hrs.

Binary Fission - unchecked

E. coli - generation time of 20 min. 20 generations (about 7 hrs.)

• 1 million cells 30 generations ( about 10 hrs.)

• 1 billion cells 72 generations ( about 24 hrs.)

• 1 x 1021 • 1,000,000,000,000,000,000,000 cells

Limiting factors in the environment Lack of food, water or nutrients space accumulation of metabolic wastes lack of oxygen changes in pH temperature

Bacterial Genetics

Genetics is the study of heredity and variation.

Bacterial genetics is used as a model to understand DNA replication, genetic characters, their changes & transfer to next generations.

Double helical structure of DNA Double helical structure of DNA

Replication

Important enzymes involved in Replication: DNA-dependent DNA polymerase.

if Error: nuclease enzyme

Restriction enzymes

Genetic Information In BacteriaCarries properties like virulence, pathogenicity & resistance

Extrachromosomal genetic material in the cytoplasm

Replicate independently

Virus infecting bacteria

Chromosome

Plasmid

Bacteriophage

PLASMIDS

Circular DNA molecules

Important vectors in genetic engineering

EPISOME • Plasmid DNA integrated with chromosomal DNA.

…………………………………………………….

• Transmissible and non-transmissible Plasmids

Mechanisms Of Genetic Variations

Mutation

Transfer or exchange of genetic material1. Transformation

2. Transduction

3. Conjugation

4. Transposition

1. Base substitution

Results of mutation -

• Missense mutation – triplet code is altered so that a different amino acid is present at a particular position in the protein.

• Nonsense mutation – converts a codon that specifies an amino acid into a termination codon.   

2. Frame Shift Mutation

Cause - Deletion or insertion of a base - changes all of the codons downstream from the change

3- Insertion

Additional pieces of DNA

Gene Transfer in bacteria:

Conjugation. Transduction. Transformation. Transposition.

Process of Conjugation

Process of Transduction

Process of Transformation

4- Tranposition.

By Transposone

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