Microbial growth kinetics, isolation, preservation & maintenance of industrial microbes Flashcards
3 setting for applied microbiology
Disease related : infection control, chemotherapy
Environmental
Industrial: Food/ Beverage, pharmaceutical and genetic engineering
Define microbes
- Unicellular, microscopic size/ invisible to naked eye
- Exist in single-celled form/ colony of cells
- Example: Viruses, bacteria, cyanobacteria, algae, fungi like mold, yeast, protozoa, larvae and egg forms of Helminths.
Importance of microbes to human
Causes diseases (medical doctors find the symptoms, diagnosis and treatment according to the microbe that is causing disease)
Involve in fermentation, used industrially
Microbial growth definition
Microbes grow, multiply by cell division and die.
Microbial growth is the result of both cell division and change in cell size.
Growth can happen in variety of physical, chemical and biological changes.
It is also the conversion of nutrients into biochemical compounds which are used as a energy source to product energy and biosynthesis. It is also called autocatalysis.
What is autocatalysis in microbes
It is also the conversion of nutrients into biochemical compounds which are used as a energy source to product energy and biosynthesis. (self-sustaining)
What are the 4 phases of microbial growth
-Lag phase
- Log growth phase
-Stationary phase
-Death phase
Lag phase description
Lag time is defined as the initial period in the life of a bacterial population when cells are adjusting to a new environment before starting exponential growth.
Occurs when cells are first introduced into fresh culture
medium
- NO increase in cell number
- Period of adaptation of cells to a new environment
- NO change in number, but an increase in mass
Cell division does not commence straight away
Cell may need to synthesize components such as ATP,
ribosomes and essential cofactors
Medium change may require new enzymes to be synthesized to use different nutrients
Cells may be injured and need to recover
Log phase description
It is a growth period of a cluster of cells in a culture medium. During this phase, there is an exponential increase in the number indicated by a section of the growth curve.
- Growth rate is higher
- Increase in cell mass and cell number with time exponentially
- Exponential phase
Period of balanced growth, in which all the components of cell grow at the same rate - Composition of biomass remains constant.
At which phase require new inoculation of microbes into new culture medium
Lag phase
What is diauxic growth
Multiple lag phases may be observed due to multiple source of carbon or nutrients.
What does length of the lag phase depend on?
Characteristics of microbial species
Media conditions
What does length of the lag phase depend on?
Characteristics of microbial species
Media conditions
Why log phase a straight line?
Growth and division occurring at the maximum possible rate given the existing conditions.
Bacteria grown at binary fission.
– Rate of growth is constant; doubling at regular intervals
– exponential growth = balanced growth
• Balanced growth - cell components are manufactured at constant rates
relative to each other
– Unbalanced growth can occur if nutrient levels or environmental
conditions change
• Unbalanced growth – rates of synthesis of cell components vary
relative to one another until a new balanced state is reached
Stationary phase description
Growth rate= Death rate
Net growth is zero
Even though net growth is zero, cells are metabolically active and product secondary metabolites
In closed systems population growth eventually ceases
and the growth curve becomes horizontal.
For bacteria this is usually when the population reaches
around 109 cells per ml
Total number of viable cells remains constant
Balance between cell division and cell death
Population may cease to divide but remain metabolically
active
Could occur for many reasons:
Nutrient limitation
Oxygen limitation
Accumulation of toxic waste products
Critical population level is reached
Death phase description
Number of cells multiplying = number of cells dying
Death Phase (Senescence)
Was originally thought to be simply the build up of
toxic end products resulting in the loss of viability
Now another suggestion :
Viable but Nonculturable (VBNC)
Cells become dormant without changes in morphology
Could resume growth if conditions change
Describe what involves in Basic Research Microbiology
By kind of organism: Microbial taxonomy, Bacteriology, Physiology, Mycology, Protozoology, Parasitology and Virology.
By Process: Microbial metabolism, genetics amd ecology.
In relation to disease: Immunology, Epidemiology and Etiology.
Briefly Describe microbial kinetics in Batch culture
Culture system containing a limited amount of nutrient, which is inoculated with the microorganism.
• Cells grow until some component is exhausted or until the environment changes so as to inhibit growth.
What is a deceleration phase
The exponential phase is followed by deceleration phase,
period of unbalanced growth.
• • In this phase, the growth decelerates due to either
depletion of one or more essential nutrients or the
accumulation of toxic by products of growth
Growth of the population is studied by analyzing the growth curve of a microbial culture grown in a closed system.
What is a closed system?
– No fresh medium added
– Nutrients decline and wastes
increase
What are sigma factors
Bacterial protein transcription factors that facilitate promoter recognition by RNA polymerase, thus enabling gene transcription ultimately, gene expression. Each RNA polymerase molecule consists of one sigma factor and a core factor (consisting of several units). The expressiona of the genes recognised by sigma factor results in the expression of useful phenotypes that protect cells from a range of stress experienced in stationary phase.
The Sigma Factors of Escherchia coli
Sigma factor 70: Housekeeping Sigma factor - recognises genes required for growth
Sigma Factor 19: The ferric Sigma factor recognizes the fec gene for iron transport.
Sigma Factor 24: Regulates and responds to extracytoplasmic functions.
Sigma Factor 28: Could of flagella and pilli synthesis
Sigma Factor 32: Controls the production of heat shock proteins.
Sigma Factor 38: Control the general stress response of cells entering the stationary phase
Sigma Factor 54: Controls the response to nitrogen limitation.
Quorum sensing
quorum sensing or quorum signalling is the ability to detect and respond to cell population density by gene regulation.
Is a energy dependent transformation.
When there is a decrease in nutrients, quorum sensing is required to produce flagerium bacteria so bacteria can move during pH changes. Quorum sensing also helps in biofilm formation.
Example of quorum sensing system
Signal molecule: Gamma-butyrolactones
Controlled Property:
Initiation of secondary metabolism and morphological differentiation
Taxonomic Group:
Streptomyces spp.
Level of sigma factors controlled by what?
Growth rate and degree of nutrient limitation
NOT biomass concentration.
At low growth rate under nutrient depletion or toxin accumulation, sigma factors are enhanced and undergo a series of energy dependent transformations to adapt to starvation conditions before source of energy is completely depleted.
Characteristics influenced by sigma factors
- Cell size: cells are smaller in stationary phase than exponential phase: hence increasing surface area to volume ratio and facilitate the enhanced uptake of limiting nutrients.
- production of detoxifying enzymes such as catalase and superoxide dismutase
- repair and protection systems including DNA repair and protein protection by chaperonins
- resistance to osmotic stress
5.
resistance to high temperatures
6.
resistance to adverse pH.
What is programmed cell death
Carefully controlled process resulting in cell death that is beneficial to development and survival of the colony. It has been observed in several prokaryotes, on grown on solidified medium enabling the development of defined colonies.
The development of streptomyces antibioticus on solidified medium involves distinct stages
- Compartmentalised young mycelium (MI) develops from germinated spores.
- Selected MI mycelium die, remaining viable segments develop into multinucleated second mycelium (MII) using substrate from dead cells.
- MII develops in the agar medium until second PCD.
Surviving MII synthesis outer hydrophobic layer and grow into the air at expense of dead cells. - The aerial mycelium produces aerial spores
What are the classes of molecular chaperones?
Hsp60s, Hsp40, Hsp90s, sHsps and Hsp70.
What are molecular chaperones?
Defined as the specialized proteins/ enzymes that interact with improperly folded polypeptides or partially folded, which corrects folding pathways or providing microenvironments for stabilization of folding intermediates and prevention of protein misfolding and aggregation. Act at stationary phase to prevent misfolding.
What is osmotic stress
During stationary phase, toxic wastes accumulate and outside the cell(bacterium) will be increasing which will dehydrate the bacteria since water will move outside.
