L4-5: MICROBIAL GROWTH AND INDUSTRIAL KINETICS

Microbial Growth

refers to an increase in the number of microbial cells

Cell Biomass

mor accurately in many industrial processes, an increase in __

Binary Fission

microorganisms growth usually occurs through ___

DNA replication, chromosome segregation, cell elongation, septum formation, two daughter cells

A typical bacterial cell undergoes:

Saccharomyces cerevisiae

bread, beer, ethanol

Lactobacillus spp.

lactic acid, fermented foods

Aspergillus niger

citric acid

Streptomyces spp.

antibiotics

Escherichia cli

recombinant proteins

Bacillus spp.

Enzymes, antibiotics

Corynebacterium glutamicum

amino acids

Growth Curve

When microorganisms are inoculated into a fresh culture medium an their population is measured over time, a characteristic ___is obtained

Lag phase, Exponential or log phase, Stationary phase, death or decline phase

Four major phases of microbial growth

Lag Phase

• cells are adapting to new environment

• cells synthesize enzymes and proteins

• DNA and RNA synthesis occur

• Cell increase in size

• metabolic activity is high

• little increase in cell number occurs

Lag Phase

A healthy and actively growing inoculum can shorten the ___

Exponential or Log Phase

• period of rapid cell multiplication

• cells divide at approx. constant rate

• nutrients are abundant

• toxic products are relatively low

• cells are metabolically active

• growth rate is at or near its maximum under the given conditions

Exponential or Log Phase

this phase is particularly important when the desired product is associated with active growth

Stationary Phase

• rate of cell formation approximately equals the rate of cell death

• nutrient depletion

• oxygen limitation

• accumulation of toxic metabolites

• changes in pH

• limited space or other environmental limitations

Stationary Phase

some industrial products, particularly secondary metabolites, may accumulate strongly during or near this phase

Death or Decline Phase

• number of viable cells decreases

• sever nutrient depletion

• toxic metabolite accumulation

• extreme pH changes

• loss of essential environmental conditions

Microbial Kinetics

quantitative study of how microorganisms grow and how growth is affected by environmental and nutritional conditions

Growth rate, Yield, Productivity

three important kinetic parameters (3)

Growth Kinetics Parameters

helps engineers and microbiologists evaluate fermentation

Growth Rate

rate at which microbial biomass increases

Yield

Amount of biomass/product obtained from the substrate consumed

Productivity

rate at which product is produced

Growth rate

how fast do the cells grow?

Yield

how efficiently is the substrate converted?

Productivity

how much product is produced per unit?

Growth rate

microbial growth

Yield

conversion efficiency

Productivity

production speed

Growth rate

determining how rapidly biomass develops

Yield

determining substrate utilization efficiency

Productivity

determining fermentation production performance

Specific Growth Rate

• represented by μ (mμ (, expresses the growth rate relative to the amount of biomass already present

u

common symbol for growth rate

Y X/S or Y P/S

common symbol for yield

QP

common symbol for productivity

h^-1

typical unit for growth rate

g/g

typical unit for yield

g/L/h

typical unit for productivity

Doubling Time

time required for the population or biomass to double

Maximum Specific Growth Rate

under favorable conditions, microorganisms have a __

Yield

tells how efficiently the substrate is converted into biomass or product

Growth-associated products

product formation occurs primarily during active microbial growth

Non-growth-associated products

product formation can occur even when significant cell growth has slowed

Productivity

how rapidly the desired product accumulates

High Productivity

high yield does not necessarily means __

Substrate, Microbial growth, Product

Industrial fermentation concept (3)

• high growth rate = rapid biomass generation

• high yield = efficient substrate utilization

• high productivity = more product produced per unity volume and time

Osmotic stress, substrate inhibition, overflow metabolism, undesirable by-products

Excess substrate can sometimes cause (4)

Temperature, pH, Oxygen, Substrate Concentration, Nutrient Availability, Toxic Metabolites

Factors affecting microbial growth kinetics (6)

Enzyme activity, membrane transport, nutrient availability, cell integrity

pH affects (4)

Monod Equation

The relationship between substrate concentration and growth is represented by models such as the

Carbon, Nitrogen, Phosphorus, Sulfur, Minerals, Vitamins or growth factors

Microbial growth requires (6) nutrients

Toxic Metabolites

• products metabolism may accumulate and inhibit growth

• one reason industrial fermentation requires careful process monitoring

Batch Culture

fixed amount of medium is initially placed in the fermenter

Inoculation, growth, product formation, harvest

General sequence of batch culture (4)

Fed-Batch Culture

• additional substrate is gradually added during fermentation

• initial medium + controlled feeding = fermentation

• widely used in industrial biotechnology

Continuous Culture

Fresh medium continuously enters while culture broth continuously leaves

Dilution Rate

key parameter of continuous culture

Continuous Culture

this provides an important connection between microbial growth kinetics and bioreactor operation

Lower Ks

__ generally indicates that the microorganism can achieve a given growth rate at a lower substrate concentration

Growth associated products

Substrate - cell growth - product

Non-growth associated products

Cell growth - metabolic development - secondary metabolite production

Product yield

Measure efficiency

Productivity

Measures speed