Bacterial Growth and Reproduction

Reproduction Bacteria can reproduce using three methods: 1. Binary Fission 2. Conjugation 3. Spore Formation

Binary Fission A form of asexual reproduction When a cell has almost doubled in size it will replicate its DNA and divide in half This produces 2 identical daughter cells Asexual reproduction does not invovle the exchange of genetic material

Binary Fission

Conjugation Is a form of sexual reproduction A long bridge of proteins forms between two bacterial cells DNA is transferred from one cell (donor) to another (recipient) Genetic Information is exchanged between individuals

Conjugation

Spore Formation Bacteria form spores during unfavorable conditions One type is called an endospore Cell forms a thick internal wall the encloses its DNA Spores can remain dormant for months or even years until conditions improve When conditions become favorable, the endospore will open, and the bacterium will grow again

Spore formation

Generation time Time required for one cell to produce two new cells. Varies depending on the type of organism and environmental conditions. Average 15 - 20 min. (varies - 10 minutes to 24 hrs.)

Bacterial Growth Increase in numbers (size of population) Constantly doubles - increases exponentially Expressed as logarithmic function of base 2 x Population doubles - 2 X - # times population doubles 1 cell reproducing every 20 min.  over 1 million cells in 7 hours  1 billion in 10 hrs.

Generation Time

Factors Affecting Bacterial Growth 1. Temperature 3. Oxygen 2. Light 4. Ph (acidity) 3. Nutrients 5. Moisture

Temperature All bacteria grow within temperature range (minimum  maximum) Most rapid reproduction occurs at the optimal temperature Starting at minimum temp. growth slowly increases Reaches maximum rate at optimum. As temp. continues to rise growth rapidly decreases.

Bacteria can be divided into 3 groups according to their growth temperature Mesophiles - 20C - 45C (50C) Ex. Environmental bacteria, pathogen Thermophiles - 45C (50) - 80C Extreme thermophiles - up to 110C Ex. Hot springs, volcanoes in ocean, decomposers Psychrophiles - 0C - 20C Ex. Cold springs, lakes; polar regions; refrigerator.

Light (Radiation) Very small group photosynthetic bacteria (cyanobacteria) - require UV light Non-photosynthetic bacteria (eubacteria) UV light is lethal (causes mutations)

Oxygen Bacteria can be divided into 3 groups based on requirement of gaseous oxygen: Aerobes - require the presence of gaseous (molecular) oxygen Anaerobes - require absence of gaseous oxygen (utilize O in oxygen containing compounds - chemical oxygen). Facultative - either condition

Nutrients Basic requirements for growth : C - building blocks of cell components N2 - production of proteins, nucleic acids H2 - occur in organic compounds O2 - involved in the production of energy Minerals, Trace Elements - required in small amounts Special metabolites ( growth factors ) Substances required for growth that the cell cannot produce using the basic requirements already listed. ( Ex. : vitamins, amino acids, carbohydrates, blood factors )

Two types of organisms based on source of nutrients Autotrophs - utilize inorganic compounds ( C - CO2, carbonates; N - NH4, N2, NO3 ) Heterotrophs - utilize organic compounds ( C - CHO, lipids; N - proteins )

Ph Concentration of H+, OH- ions 1 ------------------------- 7 --------------------------14 Acid Neutral Basic Bacteria grow within a pH range Optimum pH - pH at which maximum growth occurs

Bacteria can be divided into three groups according to PH Neutrophiles (5 -8) (optimal 7-7.2) Acidophiles (0-5) Alkalinophiles (8-12) (Soil Bacteria)

Moisture All metabolically active bacteria require presence of water: Cells largely water Most nutrients, wastes soluble in water to cross cell membrane. Site of metabolic reactions (cytoplasm)