Microbial Nutrition and Growth

Nutrition = Obtaining Required Substances from the

Environment

Essential Nutrients Must be Provided for an Organism to

Survive and Reproduce

Nutrients• Inorganic nutrients– atoms, ions or molecules

that contains a combination of atoms other than carbon and hydrogen– metals and their salts (magnesium sulfate, ferric

nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water

• Organic nutrients- contain carbon bonded to hydrogen and are usually the products of living things– methane (CH4), carbohydrates, lipids, proteins, and

nucleic acids

Macronutrients

• Required in Large Quantities

• Play principle roles in cell structure and metabolism

• Proteins (source of amino acids)

• Carbohydrates

Micronutrients

Needed in Small Amounts – like Minerals

Points about Bacterial Cytoplasm

• Mostly water

• Large proportion of protein

• 97% of dry weight is organic matter

• 96% of bacterial cell is composed of C, H, N, O, P and S

Challenge for Bacteria

How to get enough nutrients in forms that they can use to make

cell components

Bacteria Must Make

• Proteins

• Carbohydrates

• Lipids

• Nucleic Acids

Sources of Essential Nutrients

• Carbon – obtain in organic form, or reduce CO2

• Nitrogen – Fix N2 or obtain as NO3--

NO2-, or NH3

• Oxygen – Atmospheric or dissolved in water

• Hydrogen – Minerals, water, organic compounds

Nutrient Sources - Continued

• Phosphorous – Mineral deposits

• Sulfur – Minerals, H2S

• Metal Ions - Minerals

Mineral Nutrients Important in Microbial Metabolism

• Potassium – essential to protein synthesis and membrane function

• Sodium – used in some types of cell transport

• Calcium – cell wall and endospore stabilizer• Magnesium – component of chlorophyll;

membrane and ribosome stabilizer• Iron – component of proteins of cellular

respiration• Zinc, copper, nickel, manganese, etc.

Growth Factors

• Organic compounds that cannot be synthesized by an organism & must be provided as a nutrient– essential amino acids, vitamins

Nutritional Types

• Autotrophs - use CO2, an inorganic gas as carbon source

• Heterotrophs - obtain carbon in an organic form made by other living organisms

Autotrophs – “Self-Feeding”

• Phototrophs use light energy to reduce carbon or make ATP

• Chemotrophs use energy stored in inorganic chemical bonds to reduce carbon or make ATP

Heterotrophs

• Obtain reduced carbon compounds made by another organism

• Chemoheterotrophs – oxidize reduced carbon to make ATP

Two Kinds of Bacterial Heterotrophs

• Saprobes – Obtain nutrients from dead, decaying matter

• Parasites – Feed off a host organism

Environmental Influences on Microbial Growth

• Temperature

• Oxygen requirements

• pH

• Barometric pressure

3 Cardinal Temperatures

• Minimum temperature

• Maximum temperature

• Optimum temperature

3 Temperature Adaptation Groups

1. Psychrophiles – optimum temperature below 15oC, capable of growth at 0oC

2. Mesophiles – optimum temperature 20o-40oC, most human pathogens

3. Thermophiles – optimum temperature greater than 45oC

Ecological Groups by Temperature of Adaptation

Oxygen in the Microbial Environment

• Oxygen required by aerobic species (Bacillus, Pseudomonas) but produces toxic by-products; these species have efficient de-tox enzymes

• Facultative anaerobes can exist in presence of oxygen but have no requirement for it (E. coli, Staphylococcus, etc.)

Anaerobes – no Need for Oxygen

• Strict anaerobes cannot tolerate oxygen (Clostridium sp.)

• Aerotolerant anaerobes have atypical oxygen detox systems (Lactobacillus sp.)

• Capnophiles require higher CO2 pressures (Neisseria, Brucella, S. pneumoniae)

pH Effects on Growth

• Acidophiles require low pH (Thermoplasma)

• Alkalinophiles require high pH (Proteus)

Osmotic Effects

• Most microbes exist under hypotonic or isotonic conditions

• Halophiles – require a high concentration of salt

• Osmotolerant – do not require high concentration of solute but can tolerate it when it occurs

Miscellaneous Environmental Factors

• Barophiles require high environmental pressure (like deep sea Archae)

• Dehydrated Cell Stages – Spores

• Extreme radiation conditions - Dinococcus radiodurans

Ecological Relationships

• Symbiosis – existing together

• Mutualism – both parties benefit

• Commensalism – one party benefits without impacting the other

• Parasitism – one party benefits at expense of the other

• Synergism – multiple organisms working together

Microbial Biofilms

• Biofilms result when organisms attach to a substrate by some form of extracellular matrix that binds them together in complex organized layers

• Dominate the structure of most natural environments on earth

• Microorganisms communicate and cooperate in the formation and function of biofilms – quorum sensing

Ecological Relationships - Continued

• Antagonism – one party acts to inhibit or eliminate the other

• Example of antagonism:

Antibiosis – producing substances toxic to other organisms

Microbial Growth

Growth of a population at an exponential rate under optimal

conditions

Stages in Normal Growth

• Lag phase

• Exponential/log phase

• Stationary phase

• Death or decline

Mathematics of Population Growth

Growth Curve

Methods for Monitoring Growth

• Dilution Plating

• Turbidity analysis using spectrophotometer

• Direct count with hemacytometer

• Optical detection – Coulter Counter

Turbidity

Direct Microscopic Count

Electronic Counting

It is Ideal to Perform Most Manipulations of a Culture When

it is Growing in Log Phase