Microbial Nutrition and Growth

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