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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
Thank you