GROWTH OF MICROORGANISMS

Nutritional Classification

• Based upon energy and carbon sources

• Energy source- electron donors– Phototrophs (light nourishment)– Photosynthesis

Electron Donors• Chemotrophs

• Oxidation

• Reduction

• Breaking & forming bonds

Carbon Source

• Autotrophs (self)

• Heterotrophs ( different)

• Combination of terms

Photoautotrophs

• Energy(electrons) source-light

• Carbon source-CO2

• Green & purple Sulfur bacteria

Photoheterotrophs

• Energy source-light

• Carbon source –organic cpds

• Green & purple non Sulfur bacteria

Chemoautotrophs

• Energy source is oxidation -reduction reactions

• Carbon source

• Nitrifying bacteria

Chemoheterotrophs

• Energy & carbon source

• Remove electrons from H in organic cpds

• Final electron acceptor is oxygen

• Final electron acceptor is organic cpd

Physical Requirements for Growth

• Temperature-range– Psychrophiles

– Psychrotrophs

Temperature

• Mesophiles-25-40C

• Thermophiles-50-60C

• Hyperthermophiles

Determination of Range

• Maximum temperature

• Minimum temperature

• Optimum temperature is closer to max

pH

• Measures acidity or alkalinity

• Bacteria grow best at slightly alkaline pH

• Add buffers to bacterial cultures

• Molds & yeasts lower pH

Osmotic Pressure

• Microbes need water to grow

• Use salt/sugar to preserve food

• Obligate halophiles

• Facultative halophiles

Chemical Requirements for Growth

• Carbon source-50% of dry weight of cell

• Nitrogen source-amino acids, nucleic acids

Minerals

• Trace elements– Small amounts of Fe, Zn, Cu, Co etc.

– Macronutrients-S & P

• Water-medium for chemical reactions

Other Growth Requirements

• Growth factors-essential nutrients

• E. coli needs no growth factors

Other Growth Requirements

• Buffers

• A solidifying agent

Agar Advantages

• Few organisms degrade it

• Liquefies at 100 C

• Liquid until 40-50 C

• Lab-keep liquid at 50 C

• Once solidified, heat to 100 C

• Gelatin– Nutrient for some organisms– Liquefies at 35-37 C

Oxygen Requirements

• Aerobes– Use molecular oxygen for respiration– Superoxide free radicals (O. -)

– Superoxide dismutase- must have

– H2O2 is toxic

Oxygen Requirements

• Facultative anaerobes

Oxygen Requirements

• Obligate anaerobes

Oxygen Requirements

• Aerotolerants

• Microaerophiles

Growth of Bacterial Population

• Binary fission or budding

• Generation time-doubling time

Growth Curve

• Lag phase-preparing to grow

• Log phase

• Stationary phase-growth ceases

• Death Phase

Growth of a Colony

• Mass of cells –pure culture

• Some colonies are distinct

• Mixture of cells in different phases of growth

Growth of a Colony

• Location within colony determines access to oxygen

• Surface cells fully aerobic

• E. coli obtain energy aerobic respiration

• Embedded cells in center-anaerobic

Biofilms

• In nature, microbes in liquid environment

• Cells imbedded in extracellular slime– Excreted by cells

• Type of defense mechanism

Biofilms

• Quorum sensing

• Important role in infections

• Soaps & disinfectants