Dr. Magdy Muharram Associate professor of Microbiology Microbial Growth

Bacterial growth It is increase in number of bacterial cells rather than increase in size of individual bacteria. growth = increase in number of cells, not cell size One cell becomes colony of millions of cells

Factors Regulating Growth Chemical requirements: (Nutrients): Water, Carbon, Nitrogen, Sulfur, Phosphorus and Trace Elements Environmental conditions: temperature, pH, osmotic pressure Generation time

Chemical Requirements water Elements  C (50% of cell’s dry weight) and HONPS  Trace elements Organic  Source of energy (glucose)  Vitamins (coenzymes)  Some amino acids, purines and pyrimidines  Nitrogen source. In amino acids, proteins. Most bacteria decompose proteins and some bacteria use NH4 or NO3. Few bacteria use N 2 in “nitrogen fixation” take atmospheric nitrogen and form compounds. in legumes Inorganic elements Sulfur  In amino acids, thiamine, biotin. Most bacteria decompose proteins  Some bacteria use SO 4 or H 2 S. Phosphorus source  In DNA, RNA, ATP, and membranes.  PO4-2 is a source of phosphorus Trace elements  Inorganic elements required in small amounts: Usually as enzyme cofactors eg. copper, iron, magnesium

Element% dry wgtSource Carbon50organic compounds or CO 2 Oxygen20H 2 O, organic compounds, CO 2, and O 2 Nitrogen14NH 3, NO 3, organic compounds, N 2 Hydrogen8H 2 O, organic compounds, H 2 Phosphorus3inorganic phosphates (PO 4 ) Sulfur1SO 4, H 2 S, S o, organic sulfur compounds Potassium1Potassium salts Magnesium0.5Magnesium salts Calcium0.5Calcium salts Iron0.2Iron salts

Nutritional Categories Carbon sources – CO 2 = autotrophic – organic = heterotrophic Energy sources – sunlight = phototrophic – organic = chemotrophic

Chemoheterotrophic: Derive both carbon and energy from organic compounds. Chemoorganoautotrophic: Derives energy from organic compounds and carbon source from inorganic compounds. Chemolithoautotrophic: Neither sunlight nor organics used, rather it relies totally on inorganics. Saprophytic– lives on organic matter of dead organisms. Parasitic: lives on organic matter of living host = pathogens.

Environmental Factors Influencing Growth Temperature O 2 pH Osmotic Pressure and atmospheric pressure

Temperature Psychrophiles: cold-loving Mesophiles: moderate temperature-loving Thermophiles: heat-loving Each has a minimum, optimum, and maximum growth temperature. Optimum growth temperature is usually near the top of the growth range Death above the maximum temp. comes from enzyme inactivation Mesophiles most common group of organisms 5°C slows or stops growth of most microbes

Fig. 7.8

Oxygen Requirements  Obligate aerobes: require O 2  Facultative anaerobes: can use O 2 but also grow without it  Obligate anaerobes: die in the presence of O 2.  Aerotolerant: exhibit very low growth in the presence of oxygen  Microaerophilic: require low concentration of O 2

II- Chemical requirements : 1-Oxygen Some organisms need oxygen for its growth while Other cannot live if it is present and some will tolerate Can grow …..

pH Most bacteria grow between pH 6.5 and 7.5, Neutrophiles Molds and yeasts grow between pH 5 and 6 Acidophiles grow in acidic environments while Alkalophiles grow in alkaline environments Acidotolerant grow best at pH 7 but can also grow at lower pH Alkotolerant grow best at pH 7 but can also grow at higher pH below pH 4: good preservative for pickles and milk products (cheeses).

Osmotic Pressure Hypertonic environments, increase salt or sugar, cause plasmolysis Extreme or obligate halophiles require high osmotic pressure Facultative halophiles tolerate high osmotic pressure

Measuring Bacterial Growth

Microbial Division Bacteria divide by binary fission Alternative means  Budding like yeasts  Conidiospores (filamentous bacteria)  Fragmentation

Fig. 7.13

Filamentous fungi –Asexually by fragmentation of hyphae –Asexual and sexual reproduction by spores Yeasts –Asexually by budding or fission: Fission: e.g. Schizosacchromyces pombe. Budding e.g. Saccharomyces cerevisiae. –Sexual reproduction by spores (in high stress condition)

Saccharomyces cerevisiae: the budding yeast Yeasts are eukaryotic microorganisms classified in the kingdom Fungi,eukaryotic microorganisms kingdomFungi with 1,500 speciesspecies Yeasts are unicellular, although some species with yeast forms may become multicellular through the formation of strings of connected budding cells known as pseudohyphae,unicellularmulticellular pseudohyphae Yeast size can vary greatly depending on the species, typically measuring 3–4 µm in diameter, although some yeasts can reach over 40 µmµmdiameter Most yeasts reproduce asexually by mitosis, and many do so by an asymmetric division process called buddingasexuallymitosis budding

Conidiospore –Multiple (chains) or single spores formed at the end of an aerial hypha –Not enclosed within a sac –Eg: Aspergillus spp. and Penicillium spp.

Chlamydospores Arthrospores Sporangiospores Conidiospores Blastospores 1 3 1A 1B 2

Generation Time Time required for cell to divide/for population to double Average for bacteria is 1-3 hours Each microorganism has its own generation time (see table examples) E. coli generation time = min  20 generations (7 hours), 1 cell becomes 1 million cells!

Population growth Growth rate = change in cell number or cell mass it time. Generation = formation of 2 daughter cells from one cell Generation time = time for one generation to occur; generation time = doubling time Note during one generation both cell number and cell mass double

Phases of Growth Lag phase: adaptation for new conditions and making new enzymes in response to new medium. Log phase (exponential growth):the cells are growing as fast as they can, limited only by growth conditions and genetic potential. During this phase, almost all cells are alive, they are most nearly identical, and they are most affected by outside influences like disinfectants. Stationary phase: Due to nutrient depletion and/or accumulation of toxic end products, replication stops and there is no net change in cell number.by means death rate = division rate. Death phase: occurs when cells can no longer maintain viability and death exceeds division

Standard Growth Curve

Measuring Growth 1.Direct methods – count individual cells

Fig. i7.6

Serial dilution method

2.Turbidity

3.Metabolic Activity

4.Dry Weight

Basic Chemostat System

Lab Chemostat System

Culture Media Complex (contains undefined components) Chemically defined (all concentrations are known) Selective (favors the growth of a particular organism or group of organisms) Differential (has reactions that give isolates different appearance) Anaerobic (oxygen-free)

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Characteristics of Media

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