MB 251 Exam 2

What is binary fission?

Binary fission is the primary mechanism of asexual cell replication in bacteria.

What is cell expansion?

• The parent cell increases in size to ensure sufficient cytoplasm and cellular components are available for two daughter cells.

• The initial stage of binary fission where the cell increases in size to ensure there is enough cytoplasm and cellular components to distribute to two separate daughter cells
  
  

What is Chromosome replication & segregation?

•  The single bacterial chromosome is replicated into two copies, which are pulled to opposite poles of the cell using Par-A and Par-B proteins.

• The cell duplicates its single chromosome into two copies. In most bacteria, these copies are pulled to opposite poles of the cell using Par-A and Par-B proteins

What is Cytokinesis?

• Ring structures formed by FtsZ protein filaments assemble at the cell center and constrict inward to pinch the cell into two separate daughter cells.

• The division of the cell center, driven by a mesh of FtsZ filaments that assemble into a ring around the midpoint and constrict inward until the cell pinches into two

What is Cell wall synthesis?

• The cell synthesizes new peptidoglycan at the division plane to complete wall formation between the new cells.

• Simultaneous with cytokinesis, the cell synthesizes new peptidoglycan to form a dividing cell wall between the two emerging daughter cells
  
  

What is the Growth rate of bacteria?

Growth rate measures how quickly a bacterial cell completes binary fission to double its population.

What is exponential growth?

Under optimal conditions, bacteria grow exponentially, meaning the population doubles every generation 1→2→4→8

What is generation time?

• Fixed time it takes for a cell to grow and divide into two cells (must have unlimited resources)

• The time required for a population to double. Generation times vary significantly by species and environment (e.g., E. coli takes 20 minutes under optimal conditions vs. 60 minutes under non-optimal conditions; Mycobacterium tuberculosis takes 15 to 20 hours).

What is the generation time equation?

G= t/n

• g= generation time

• t= time

• n= number of generations

What is the exponential growth equation?

b= Bx2^n

• b= final number of bacteria

• B= starting number of bacteria

• n= number of generations

What is the batch culture environment in the phases of growth?

• Batch Culture Environment: When bacteria grow in closed laboratory systems (batch cultures), no fresh nutrients are added and no waste products are removed.

• A closed laboratory culture system where no additional fresh nutrients are supplied and no metabolic waste products are removed.

 

Under the conditions of batch culture environment what are the 4 predictable growth phases?

• Under these conditions, bacterial populations follow a predictable four-phase growth pattern: lag phase, log phase, stationary phase, and death phase.

 

When does the lag phase occur?

Occurs when bacteria are introduced into a new environment

Is bacteria replicated in the lag phase?

no

What is the activity of the lag phase?

• Cells adapt to environmental changes (such as temperature or nutrient availability) by synthesizing required proteins and enzymes.

• Considered an adaption period as bacteria adjust to the new envrionment

  • Synthesizing enzymes and proteins needed to adapt to the new conditions

• Binary fission does not occur during this phase; cells adapt to new environmental settings (such as shifted temperatures or available nutrients) and synthesize the specific proteins required for survival and future division

What does the lag phase depend on?

• Depends on the species and how significantly the new environment differs from the old one.

• Bacterial species

• How different the new environment is from the previous environment

• State of the cells themselves

What is the maximal division of the exponential (log) phase?

•  Cells grow and divide via binary fission at a constant, exponential rate by consuming available nutrients.

• Population most uniform during this time

What is the rate of growth in the exponential (log) phase?

• Rate of growth is constant and at maximal rate based on conditions available

  • Calculation of generation (doubling) time

  •  Generation time and growth rate equations are calculated using data strictly from this phase.

What is the growth of the stationary phase?

• The total population count stabilizes because the rate of cell division equals the rate of cell death.

• Population growth ceases

  • Combination of active cells slow reproduction and death rate equals growth rate

What is the cause of the ceases of population growth in the stationary phase?

• Nutrients become depleted and toxic metabolic wastes accumulate in the batch culture.

• Due to:

  • Nutrient/oxygen limitation

  • Toxic waste accumulation

  • Critical population density

• Cells produce secondary metabolites

What is the secondary mechanism of the stationary phase?

Bacteria produce molecules non-essential for basic growth—such as antimicrobials, antibiotics, and toxins—to kill neighboring microbes and secure scarce resources.

What is the population decline of death phase?

•  Toxic waste accumulation and severe nutrient depletion cause the cell death rate to exceed the rate of binary fission.

What is the cell death rate in the death phase compared to the growth rate?

• Cell death rate is greater than growth rate

  • Fraction of population genetically programmed to die

What is the long-term stationary of Death phase?

• Total population may never reach zero cells- some survive off cell debris from dying cells

• Successive waves of genetic variations (bacterial evolution)

•  The population decreases but never reaches absolute zero. Surviving cells sustain themselves by consuming nutrients released from dying, lysing cells, or by gaining beneficial mutations.

 

What are the chemostat systems of continuous culture?

• Industrial vessels continuously add fresh media and remove accumulated waste products.

• Continuous culture grown in a chemostat

  • Allows cells to be kept at constant growth rate and cell mass

What is the environmental control of continuous culture?

• Parameters such as pH, temperature, and oxygen levels are actively regulated.

• Chemostats actively regulate parameters such as pH, temperature, and oxygen concentration to sustain a steady growth rate and cell mass.

What us the use and requirements of continuous culture?

• Maintains bacterial cultures indefinitely in log phase to continuously produce commercially valuable products (such as vitamins and antimicrobials).

• Must have continuous addition of nutrients and removal of waste

• Advantageous for industrial microbiology

• Used primarily in industrial microbiology to maintain bacterial populations indefinitely in a single constant phase of growth, enabling continuous production of commercially valuable products like vitamins or antimicrobials. It requires specialized vessels called chemostats that continuously supply fresh nutrients/oxygen while removing accumulated waste products
  
  

What is the structure of Biofilms?

• Complex, dynamic microbial communities attached to surfaces and to each other, often comprising hundreds of distinct bacterial species.

• Complex and dynamic ecosystem

  • Highly structured communities

  • cells suspended in an extracellular matrix of extracellular chemicals or antibodies

What is extracellular matrix of biofilms?

• Cells are encased in self-produced

• 
  

What is extracellular polymeric substances in biofilms?

• , a polysaccharide-rich gel that protects bacteria from destruction, antibiotics, and chemical agents.

• Microbes in a biofilm secrete an extracellular matrix made of Extracellular Polymeric Substances (EPS). EPS is a polysaccharide-rich gel that maintains the structural integrity of the biofilm while protecting encased cells from chemical agents, antibiotics, and destruction

What type of community are biofilms?

• Dynamic, heterogenous community of microbes that adhere and grow on solid surfaces

  • How many microbes grow in nature

• Hard to destroy because cells are protected from chemicals or antibiotics

What do cells use in order to coordinate biofilm formation?

• Cells use quorum sensing to coordinate the biofilm formation

  • controls gene expression based on cell density

What is stage 1 of biofilm formation?

1. Reversible Attachment: Planktonic (free-floating) cells loosely bind to a surface.

What is stage 2 of biofilm formation?

Irreversible Attachment: Cells secrete EPS, permanently anchoring themselves to the surface.

What is stage 3 of biofilm formation?

Growth & Division: Bound cells multiply and continuously expand the EPS matrix.

What is stage 4 of biofilm formation?

Maturation: The biofilm forms complex structures containing water channels to deliver nutrients to deep cells.

What is stage 5 of biofilm formation?

Dispersal: Outer cells revert to planktonic growth and slough off to colonize new locations.

What is quorum sensing?

• Uses autoinducers to control gene expression in response to bacterial cell number

• A cell-to-cell communication mechanism bacteria use to detect population density and coordinate collective actions. Cells continuously secrete signaling molecules called autoinducers; as cell density rises, autoinducers accumulate, re-enter cells, and activate specific genes responsible for EPS production, biofilm maturation, or toxin release
  
  

What is cell communication of quorum sensing?

: A density-dependent mechanism bacteria use to coordinate group behaviors.

What are low density autoinducers of quorum sensing?

• Low Density: Autoinducers diffuse away harmlessly into the environment.

• When cell density is low, bacteria produce low amounts of autoinducers, allowing the signaling molecules to diffuse away into the surrounding environment without triggering gene expression.

What is high density of quorum sensing?

High Density: Autoinducers accumulate to high concentrations, re-enter bacterial cells, and trigger specific gene expression.

What is the different process of quorum sensing?

• Regulated genes can control different processes

  • 1. Biofilm formation

  • 2. Toxin production

  • 3. Luciferease production

• Regulated Behaviors: Coordinates EPS secretion for biofilm maturation, toxin release (e.g., cholera toxin by Vibrio cholerae), and bioluminescence (luciferase production).

Prokaryotes are the most what on Earth?

Prokaryotes are the most metabolically and physiologically diverse organisms on earth

What are the nutritional and energy requirements of Prokaryotes?

• All living organisms require a means to generate energy, along with essential nutrient building blocks (carbon, oxygen, nitrogen, and hydrogen) to construct macromolecules such as proteins and nucleic acids.

• Energy supply

What are essential nutrients?

• Elemental building blocks that must be obtained from the environment

  • Macronutrients- C, N, O, H, P, S

  • Micronutrients- Mg²+, Fe²+, K+ plus others

What is suitable habitat (environmental conditions) for prokaryotes?

• Physical parameters

  • pH, temperature, osmolarity, pressure

  • Proteins fold into their functional shape only in certain conditions → affects growth rate

• Chemical parameters

  • O2 nutrients

• Growth requires a suitable habitat supplying the correct physical parameters (pH and temperature) and chemical parameters (oxygen and nutrients).

 

What is the influence of environment on growth?

• Organisms can be classified based on their environmental growth requirements

  • Water activity (Solute/salt concentration_

  • pH

  • Temperature

  • Oxygen concentration

What is the physiological diversity of prokaryotes?

Prokaryotes are highly diverse and inhabit extreme environments across the planet, including deep-sea thermal vents and hot springs at Yellowstone.

What is the protein folding of prokaryotes?

Microbes require specific environmental parameters because their cellular proteins fold into correct, functional shapes only within their optimal habitats

What are the 4 environmental of prokaryotes?

Four key factors affect microbial growth: three physical factors (water activity, pH, and temperature) and one chemical factor (oxygen concentration).

What is water activity?

Water activity (\(a_w\)) measures the available water in an environment, where pure water has a value of 1. Related to the amount of water vapor pressure in a substance.

What is pure distilled water?

Aw= 1

What Aw is bacteria typically requiring?

Aw= 0.91

• Most bacteria require a water activity greater than 0.91.

What Aw is fungi typically require?

Aw= 0.7

• Fungi tolerate drier environments (water activity ~0.7), allowing molds to grow on dry bread where bacteria cannot.

What is the comparison of solute to Aw?

Higher the solute the lower the Aw

What is a hypotonic solution?

higher water activity

What is a hypertonic solution?

lower water activity

What is the solute impact of water activity?

• Dissolving solutes like sugars or salts increases solute concentration and decreases water activity.

• Honey has a low water activity (0.5 to 0.6) due to high sugar levels, making it an effective antiseptic that inhibits microbial growth.

• Drying foods (e.g., beef jerky) reduces water activity to prevent bacterial growth and spoilage.

Halophiles grow optimally in what?

• Grow optimally in presence of NaCl or other salts at concentration above 0.2 M

• "Salt-loving" microbes that require salt to grow, with an optimal salt concentration of approximately 0.2 M sodium chloride (NaCl). Standard ocean microbes grow at ~0.4 to 0.6 M salt.

What do extreme halophiles require?

• Require 2-6 M salt concentrations (.75 aw)

•  (about 10 times saltier than seawater) and live in habitats like the Great Salt Lake and the Dead Sea. They produce protective pigments that turn salt lakes pink.

What doe cellular macromolecules require high salt to what?

To maintain stability and activity

What are halotolerant?

 Microbes that do not require salt for growth (optimal at low solute levels), but can tolerate higher salt concentrations (e.g., skin flora).

What is the growth rate of Halophiles?

Microbes achieve their highest growth rates at their optimal salt concentration but can grow at reduced rates across lower or higher ranges.

What is the growth optimum pH of Acidophiles?

• pH of 0-5.5

• Grow optimally at low pH levels between 0.5 and 5 (typically around pH 3 to 4, similar to grapefruit juice).

What is the growth optimum pH of Neutrophiles?

• pH between 5.5-7

•  Grow optimally in neutral environments between pH 5.5 and 7 (similar to human cells).

What is the growth optimum pH of Alkaliphiles (alkaliphiles)?

• pH between 8.5-11.5

• Prefer basic environments, growing optimally between pH 8 and 11 (similar to ammonia or baking soda).

What maintains neutral internal pH

• Plasma membrane impermeable to protons

• Potassium proton pump

•  Microbes maintain cytoplasmic neutrality by either altering their immediate external environment (producing basic or acidic waste products) or adjusting proton (\(H^+\)) concentrations within their cytoplasm.

What maintains acid tolerance?

• Pumps protons out of cell

• Produce acid shock proteins to protect folding of cellular proteins

What can be produced in order to change the pH of environment?

By producing acidic or basic waste products

What is the internal neutrality of acidophiles and alkaliphiles?

Although acidophiles and alkaliphiles live in extreme external pH environments, their internal cytoplasmic pH remains neutral.

What are the distinct cardinal growth temperatures?

Minimal, maximum, optimal

What happens when temperatures are above maximal levels?

• Temperatures above maximal inhibit enzyme function and are lethal

•  Increasing temperatures past the optimum causes a sharp drop in growth. High heat denatures (unfolds) cellular proteins and collapses the cytoplasmic membrane due to excess fluidity, killing the cell.

• Protein denaturation cytoplasmic membrane collapse thermal lysis

What happens when temperatures are minimum levels?

• Temperatures below minimum, not necessarily lethal

•  As temperatures drop below optimum toward minimum, growth slows gradually. Below the minimum temperature, the plasma membrane solidifies into a gel-like consistency, stopping growth without killing the cell; warming can resuscitate frozen microbes (e.g., permafrost samples).

• Membrane gelling

What is the temperature range of Psychrophiles?

0 to 20 degrees Celsius

What is the temperature range of Mesophiles?

20 to 45 degrees Celsius

What is the temperature range of Thermophiles?

55 to 85 degrees Celsius

What is the temperature range of Hyperthermophiles?

85 to 113 degrees Celsius

What are Thermophiles and hyperthermophiles specific evolutionary adaption to survive extreme heat without protein or membrane faliure?

• Protein Stabilization: Proteins contain a higher number of hydrogen bonds and proline amino acids (which form disulfide bonds) to maintain structure.

• Chaperones: Chaperone proteins assist in keeping cellular proteins properly folded.

• DNA Protection: DNA structure is stabilized to prevent double strands from separating.

• Membrane Integrity: Plasma membranes incorporate longer, saturated (higher molecular weight) fatty acids to prevent melting.

What is thermophile adaptions of protein stabilization?

• More H-bonds

• More proline

• More chaperones to help folding

What is DNA stabilization of thermophile adaptions?

Histone-like proteins

What is membrane stabilization of thermophile adpatations?

More saturated, high MW lipids

What does growth depend on in Oxygen concentration?

• Metabolic processes, electron transport chains, and terminal electron acceptors

• Enzymes for reactive oxygen species

  • Superoxide dismutase, catalase, peroxidase

• Oxygen requirements depend on whether a microbe uses an electron transport chain requiring oxygen for energy production. Because oxygen metabolism produces toxic Reactive Oxygen Species (ROS) (such as hydrogen peroxide and superoxides), oxygen-utilizing cells must produce detoxifying enzymes (superoxide dismutase [SOD], catalase, and peroxidases).

What is obligate aerobes?

Require oxygen for energy; possess ROS detoxifying enzymes; grow exclusively at the top of liquid culture tubes where oxygen diffuses.

What are obligate anaerobes?

 Do not use oxygen for metabolism and lack ROS detoxifying enzymes; oxygen is toxic and kills them; grow only at the bottom of culture tubes.

What are facultative anaerobes?

Grow with or without oxygen; possess ROS detoxifying enzymes; produce more ATP and grow faster in the presence of oxygen; grow throughout the tube with dense growth at the top.

What are Aerotolerant anaerobes?

 Do not use oxygen for metabolism, but possess ROS detoxifying enzymes; oxygen is not toxic, so they grow evenly throughout the tube.

What are microaerophiles?

 Require oxygen for growth, but possess less effective detoxifying enzymes that are easily overwhelmed by high atmospheric oxygen; grow slightly below the liquid surface where oxygen levels are lower.

What must a lab do in order for microbes to grow?

• must provide correct nutrient

•  To cultivate microbes in a laboratory, all of their specific physical and chemical environmental growth conditions must be provided.

For bacteria you can classify media based on what?

• Chemical composition

• Physical nature

• Function

Why can’t many microbial species be grown in a laboratory setting?

Many microbial species cannot currently be grown in a laboratory setting because their exact natural environmental requirements remain unknown.

What must you provide for the host cells in viruses for them to grow in?

• In vivo- host cells provided by who living organism

• In vitro- cell grown in an artifical envrionment

  • Primary cell culture- cells freshly obtained from organs/tissue

  • Continuous cell lines- transformed cells able to be grown “indefinitely”

What is viral cultivation?

 Viruses cannot be grown on standard cell-free bacterial media and require living host cells to replicate. They are cultivated either in vivo (inside living organisms) or in vitro (in artificial cell cultures).

What is a defined media?

• All components and amounts known

•  Media in which the exact chemical identity and precise quantity of every component are known.

What is complex media?

• do not know exact composition

•  Media in which the general composition is known, but the exact molecular structures and precise amounts of ingredients vary. For example, media containing peptone (digested soybean) supplies amino acids, but the exact types and quantities are undefined.

What are the functional classifications of bacterial media?

• General purpose

• Enriched Media

• Selective Media

• Differential Media

What is general purpose (tsa)

• supports growth of many microorganisms

•  Media formulated to support the growth of a wide variety of different microbial species.

What is enriched media (blood sugar)?

• General purpose media supplemented with special nutrients

• General purpose media supplemented with specific nutrients to foster the growth of fastidious microbes.

What is selective media (MacConkey)?

• Only allows specific types of organisms to grow

•  Media containing components that inhibit the growth of specific organisms while allowing others to grow. For example, MacConkey's agar inhibits gram-positive bacteria (such as Staphylococcus aureus) while selecting for gram-negative bacteria.

What is differential media (MacConkey)?

• Allows you to distinguish between groups of microbes

• Media designed to distinguish between different species of bacteria based on observable metabolic differences. For example, MacConkey's agar differentiates lactose fermenters (which produce acid and turn colonies/media pink or red) from non-lactose fermenters (which appear yellow).