Bacterial Physiology By Dr. Zubaida Najat Mustafa

Microbial Growth: Refers to an increase in cell number, not in cell size. Bacteria grow and divide by binary fission,a rapid and relatively simple process. In which parent cell divides to form a progeny of two cells

Microbial Growth

Microbial Growth

Requirements for Growth Physical Requirements 1. Temperature: Microbes are loosely classified into several groups based on their preferred temperature ranges. A. Psychrophiles: “Cold-loving”. Can grow at Two groups:

1-Temperture A-Psychrophiles: 1- True Psychrophiles: Sensitive to temperatures over20˚. Optimum growth at 15C ˚ or below. Found in very cold environments (North pole, ocean depths). Seldom cause disease or food spoilage. Psychrotrophs: Optimum growth at 20 to 30C˚. Responsible for most low temperature food spoilage.

1- Temperture B. Mesophiles Mesophiles: “Middle loving”. Most bacteria. Include most pathogens and common spoilage organisms. Best growth between 25 to 40oC. Optimum temperature commonly 37oC. Many have adapted to live in the bodies of animals

1. Temperature: C. Thermophile C. Thermophiles: “Heat loving”. Optimum growth between 50 to 60oC. Many cannot grow below 45oC. Adapted to live in sunlit soil, compost piles, and hot springs. Some thermophiles form extremely heat resistant endospores.

1. Temperature: C. Thermophile Extreme Thermophiles (Hyperthermophiles): Optimum growth at 80oC or higher. Archaebacteria. Most live in volcanic and ocean vent

Requirements for Growth Physical Requirements 2. pH: Most bacteria prefer neutral pH (6.5-7.5). Acidity inhibits most microbial growth and is used frequently for food preservation (e.g.: pickling). Alkalinity inhibits microbial growth, but not commonly used for food preservation. Acidic products of bacterial metabolism interfere with growth

Requirements for Growth Physical Requirements 2. pH Organisms can be classified as: A. Acidophiles: “Acid loving”. Grow at very low pH (0.1 to 5.4) example Lactobacillus produces lactic acid B. Neutrophiles: Grow at pH 5.4 to 8.5. u Includes most human pathogens. C. Alkaliphiles: “Alkali loving”. Grow at alkaline or high pH (7 to 12 or higher) example Vibrio cholerae and Alkaligenes faecalis optimal pH 9.

Requirements for Growth Physical Requirements 3. Osmotic Pressure Cells are 80 to 90% water.. Hypertonic solutions: High osmotic pressure removes water from cell, causing shrinkage of cell membrane (plasmolysis). Used to control spoilage and microbial growth. Sugar in jelly. u Salt on meat. B. Hypotonic solutions: Low osmotic pressure causes water to enter the cell. In most cases cell wall prevents excessive entry of water. Microbe may lyse or burst if cell wall is weak.

Requirements for Growth Physical Requirements 3. Osmotic Pressure Halophiles: Require moderate to large salt concentrations. Ocean water contains 3.5% salt. Most bacteria in oceans. Extreme or Obligate Halophiles: Require very high salt concentrations (20 to 30%). u Bacteria in Dead Sea, brine vats Facultative Halophiles: Do not require high salt concentrations for growth, but tolerate 2% salt or more.

Requirements for Growth Chemical 1. Carbon: Makes up 50% of dry weight of cell. Structural backbone of all organic compounds. Bacteria obtained carbon in two maine way:- Heterotrophs: Obtain carbon from their energy source: lipids, proteins, and carbohydrates. Autotrophs and Photoautotrophs: free living Obtain carbon from carbon dioxide.

Requirements for Growth Chemical Requirements 2 Requirements for Growth Chemical Requirements 2. Nitrogen, Sulfur, and Phosphoru A. Nitrogen: Makes up 14% of dry cell weight. Used to form amino acids, DNA, and RNA. Sources of nitrogen: Protein: Found in organic matter u Nitrogen gas (N 2 ): Obtain N directly from atmosphere. Important nitrogen fixing bacteria, live free in soil or associated with legumes (peas, beans, alfalfa, clover, etc.). Legume cultivation is used to fertilize soil

Requirements for Growth Chemical Requirements 2 Requirements for Growth Chemical Requirements 2. Nitrogen, Sulfur, and Phosphorus Used to form proteins and some vitamins (thiamin and biotin). Sources of sulfur: Protein : Most bacteria Hydrogen sulfide u Sulfates: Salts that dissociate to give SO 4 Phosphorus: Used to form DNA, RNA, ATP, and phospholipids. Sources: Mainly inorganic phosphate salts and buffers.

Requirements for Growth Chemical Requirements Other Elements: Potassium, magnesium, and calcium are often required as enzyme cofactors. Calcium is required for cell wall synthesis in Gram positive bacteria. . Trace Elements:. Many are used as enzyme cofactors . Usually metals needed in very little amount but are critical to cell function e.g. Nickel(Ni), selenium (Se), Tungsten ( W), copper (Cu), Cobalt (Co).

Organic Growth Factors Organic compounds obtained from the environment and needed in very small amount only by some cells Vitamins, amino acids, purines, pyrimidines

Requirements for Growth Chemical Requirements Oxygen A. Obligate Aerobes: Require oxygen to live. B. Facultative Anaerobes: Can use oxygen, but can grow in its absence. Have complex set of enzymes. Examples: E. coli, Staphylococcus, yeasts, and many intestinal bacteria. C. Obligate Anaerobes: Cannot use oxygen and are harmed by the presence of toxic forms of oxygen. Examples: Clostridium bacteria that cause tetanus and botulism.

Toxic Forms of Oxygen Utilization of O2 during metabolism yields toxic by-products including singlet oxygen:(1O2), superoxide free radicals (O2), hydrogen peroxide (H2O2) and Hydroxyl radical(OH). Toxic O2 products can be converted to harmless substances if the organism has catalase (or peroxidase) and superoxide dismutase (SOD) enzymes.

Anaerobic Culture Methods Candle jar CO2-packe

Capnophiles require high CO2

Microbial Growth Culture Media Culture Medium -Culture Medium: Medium containing nutrients that support microbial growth -Sterile: No living microbes -Inoculum: Introduction of microbes into medium -Culture: Microbes growing in/on culture medium Types of Culture Media Enrichment Culture Nutrient media Special media Selective Media Differential Media Selective and Differential Media

Microbial Growth Phases of Growth Bacterial Growth Curve: When bacteria are inoculated into a liquid growth medium, it regulated by nutritional environment . Four phases of Bacterial Growth:

1. Lag Phase a- Period of adjustment to new conditions. b- Little or no cell division occurs, population size doesn’t increase. C- May last from one hour to several days

2- Log Phase: Cells begin to divide and generation time reaches a constant minimum. Period of most rapid growth. Number of cells produced > Number of cells dying Cells are at highest metabolic activity. Cells are most susceptible to Antibiotics

3- Stationary Phase (Growth rate = death rate) Population size begins to stabilize. Number of cells produced = Number of cells dying Overall cell number does not increase. Cell division begins to slow down. Note/ Factors that slow down microbial growth: Accumulation of toxic waste materials Acidic pH of media Limited nutrients Insufficient oxygen supply (Growth rate = death rate)

4- Death or Decline Phase Population size begins to decrease. Number of cells dying>Number of cells produced Cell number decreases at a logarithmic rate. Cells lose their ability to divide. A few cells may remain alive for a long period of time death rate is greater than growth rate

Bacterial genetics Genetics is the study of inheritance and variation. All inherited characteristics are encoded in DNA, except in RNA viruses The bacterial chromosome The bacterial chromosome contains the genetic information that defines all the characteristics of the organism. It is a single, continuous strand of DNA with a closed, circular structure attached to the cell membrane of the organism.

Replication Chromosome replication is an accurate process that ensures that the progeny cells receive identical copies from the mother cell. The replication process is initiated at a specifc site on the chromosome(oriC site ) where the two DNA are locally denaturated

Genetic variation in bacteria can occur as a result of mutation or gene transfer. 1- Mutation A mutation is a change in the base sequence of DNA, as aconsequence of which different amino acids are incorporated into a protein, resulting in an altered phenotype. A- Frame shift B- Insertion

Gene Transfer:Recombination The transfer of genetic information can occur by: A-conjugation B- transduction C- transformation D- transposition The result is a recombinant cell that has a genome different from either the donar or the recipient.

Conjugation in E.coli Is the process by which bacteria transfer genes from one cell (Donor-male ) to the recepient(female) by cell to cell contact

Transformation:- Is the process a free double stranded DNA enters the recepient cell . One of the two strand destroy by cell nuclease , the remaing single strand invade the resident chormosome seeking a homologous sequence Conjugation in E. coli

Transduction by a Bacteriophage Is the process transferring of gene from one cell to another Via a Phage without cell to cell contact

Transposons Transposons, also called jumping genes, are pieces of DNA that move readily from one site to another, either within or between the DNAs of bacteria, plasmids and bacteriophages. In this manner, plasmid genes can become part of the chromosomal complement of genes

Plasmide Plasmids are extrachromosomal double-stranded circular DNA molecules . They are capable of replicating independently of the bacterial chromosome i.e. they are (replicons). Plasmids occur in both Gram-positive and Gram- negative bacteria, and several different plasmids can often coexist in one cell.

Plasmids

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