Microbiology Chapter 4: Microbial Growth

Exponential growth

Growth of a microbial population in which cell numbers double within a specific time intervenal

Exponential growth equation

N = N₀* 2ⁿ

What does the N mean in the exponential growth equation

Final cell number

What does N0 mean in the exponential growth equation?

Initial cell number

What does n meaning in the exponential growth equation

The number of generations during the period of exponential growth

With exponential population growth, what is happening

The population is doubling every generation

Generation time

time required for microbial cells to double in number

What is the range of generation time

10 mins to several hours/days

Generation time equation

g = t/n

What is t in the generation time equation

The duration of exponential growth (days/hours/minutes)

What is n in the generation time equation?

The number of generations during the period of exponential growth

instantaneous growth rate constant (k)

expresses the rate at which the population is growing at any instant

What is the equation of specific growth rate

k = 0.693/g

Growth in an open system

- continual provision of nutrients

- continual removal of wastes

What happens to cells in an open system during log phase

They remain at a constant biomass concentration for extended periods

Microtubules

The biggest kind of protein structure

Helps support the cell and maintain the position of organelles

Intermediate filaments

Second largest protein structure

Makes up the framework of cell

Confers the shape and size of the nucleus

Helps cells withstand strand

Actin

The smallest protein structure

• Helps support the plasma membrane

• Involved in cell motion

• Involved in cell division

What kind of reproduction do eukaryotic microbes undergo

Asexual and sexual with haploid or diploid progeny

What kind of reproductive strategy do Bacteria and Archaea do

Asexual reproduction with haploid progeny only

What is conjugation considered/why isn’t it considered sexual reproduction

It is considered “variability assurance”

What does the growth of cellular constituents result in

• An increase in cell size

• An increase in cell number

What does the growth in bacteria refer to

Population growth rather than growth of individual cells

Binary fission

Cell division following enlargement of a cell to twice its minimum size

Septum

A partition between dividing cells, pinches off between two daughter cells

What is the difference between bacterial growth and binary fission?

Growth results in an increase in the number of cells while binary fission results in cell division

Generation time

Time required for microbial cells to double in number

What does the generation time of bacterial cells depend on

Nutritional and genetic factors as well as temperature

What does the daughter cells of bacteria get at the end of cell division

Receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell

Two pathways of bacterial cell cycle

1. DNA replication and partition

2. Cytokinesis

What bacteria have cell cycles that are studied extensively

E. coli, Bacillus subtilis, and Caulobacter crescentus

Origin of replication in bacteria

Only one; site at which replication begins

Terminus

Site at which replication is terminated, located opposite of the origin

Replisome

Group of proteins needed for DNA synthesis. These proteins push daughter chromosomes to opposite ends

In what direction does DNA replication proceed in bacterial cells

In both directions from the origin

SMC proteins

Structural maintenance of chromosomes proteins. These proteins aid in the condensation of daughter chromosomes by pulling DNA molecules to each end

MreB

Murein cluster B is an actin homolog that plays a role in determining cell shape and chromosome segregation

Determines cell diameter and elongation as Z ring forms in the center in cocci bacteria

What do new origins of replication associate with

They associate with MreB tracks

What happens if MreB is mutated

The chromosomes don’t segregate

Septation

Formation of cross walls between daughter cells

What are the steps of septation

1. Selection of a site for septum formation

2. Assembly of a Z ring

3. Linkage of the Z ring to plasma membrane (cell wall)

4. Assembly of cell wall synthesizing machinery

5. Constriction of cell and septum formation

FtsZ

A protein that serves as a tubulin homologue; its polymerization forms the Z rings and thus filaments of meshwork

MinCDE system

Made up of MinC, MinD, and MinE that oscillate from one side of the cell to the other. Links the Z ring to the cell membrane

Z ring

Constricts and results in the cell wall synthesis of septal wall

FtsA, ZipA

Anchors Z ring to plasma membrane F

FtsK

Aids in chromosomes segregation and separation of chromosome dimers

FtsQLB

May provide a scaffold for assembly of proteins involved in peptidoglycan synthesis

FtsL and FtsW

Aids in peptidoglycan synthesis

FtsN

Thought to trigger constriction initiation

What is cellular growth and shape determined by

Peptidoglycan synthesis of bacteria

PBPs

Penicillin binding proteins.

They link peptidoglycan strands and catalyze controlled degradation for new growth

Autolysins

Enzymes of PBPs

Degrade peptidoglycan and site new units added

Cocci divisome

New peptidoglycan forms only at central septum.

FtsZ determines site of cell wall growth and may also recruit PBPs for synthesis of the septum

Rods

Are similar to FtsZ proteins but elongate prior to septation

What does vibrio MreB do

Has helical polymerization throughout the cell

Crescentin

An intermediate filament homologue

Localizes to short, curved side of cell

Asymmetric cell wall synthesis forms from the curve

Batch Culture

A closed-system microbial culture of fixed volume

What are the four phases of a bacth culture

1. Lag phase

2. Log phase

3. Stationary phase

4. Death phase

Lag phase

Period in which the metabolism is happening but no cell division occurs

Tublin

A protein that is the main constituent of living cells

• Provides structural support for the cell

• A pathway for transport

• Can force generation in cell division

Log phase

Bacteria dividing exponentially

Stationary Phase

As division occurs, bacteria uses up media and excrete waste. Some bacteria begin to starve while others die from toxic waste

Death Phase

Excess of waste and starvation, Bacteria die off faster than they can reproduce

Chemostat

A type of continuous culture device that enables control over both the specific growth rate and growth yield of a microbial culture. Fresh sterile medium is added to a culture vessel and spent media is washed out at equal rates, resulting in a culture that maintains a fixed volume

Oligotrophic environment

An environment with low nutrient concentrations

Sessile

Attached to surfaces

Extracellular Polymeric Substance

Formed from polysaccharides, proteins, and DNA

First step of biofilm formation

The substratum is preconditioned by ambient molecules

Second step of biofilm formation

Cells deposist

Third step of biofilm formation

Cells adsorb to the surface of the substratum

Step Five of Biofilm Formation

Cells signal to one another for form the extracellular polymer substance

Sixth step of biofilm formation

Nutrients and O₂ are transported

Seventh Step of biofilm formation

The cells begin to replicate and grow

Eighth step of biofilm formation

The cells secrete the polysaccharide matrix

Ninth step of biofilm formation

The cells detach, erode the surface, and slough

Sessile growth

Growth of microbes that are attached to surfaces

Planktonic growth

Growth of free-floating or free swimming cells

Biofilm

A population of cells enmeshed in a polysaccharide matrix that is attached to a surface

What is heterogeneity in biofilms

Differences in metabolic activity and locations of microbes

What protects microbes from harmful agents in biofilms

The EPS and change in the attached organisms’ physiology

What are harmful agents to microbes in biofilms

UV light, antibiotics, and antimicrobials

What can sloughing off of organisms in biofilms result in

Contamination of water phase above the biofilm such as in a drinking water system

Psychrotolerant

Also known as psychrotrophs; organisms that can grow at 0 degrees Celsius but have an optima of 20 degrees to 40 degrees Celsius

What kind of sheet do cold organisms typically have in their pro tie ins

More A-helices than B-sheets

Quorum Sensing

Density-dependent communication between bacterial cells. A regulatory mechanism that assesses population density. Bacterial cells produce small proteins that increase in concentration as microbes replicate and convert a microbe to a competent state

Bacteriocins

Bacterial proteins

What does accumulation of signaling molecules from quorum sensing result in

Coordinated group behaviors

Acylhomoserine lactone (AHL)

An autoinducer molecule produced by many gram-negative organisms

What does acylhomoserine lactone do

It can diffuse across plasma membranes and induce the expression of target genes that regulate a variety of functions

Why do some bacteria use quorum sensing

To ensure that sufficient cell numbers of their own species are present before initiating activities that require a certain cell density to work effectively

Autoinducers

A specific molecule employed by species that use quorum sensing. Can diffuse into the cell and can bind to a specific transcriptional activator protein or a sensor kinase of a two-component system ultimately triggering transcription of specific genes

Types of quorum sensing systems

Symbiosis, DNA uptake, and pathogenicity and increased virulence factor production

A symbiosis quorum sensing system

Bioluminescence caused by Vibrio fischeri and squids

Cardinal temperatures

The minimum, optimum, and maximum temperatures at which an organism grows

Psychrophile

Optimal growth temperatures with a maximum between 15-20 degrees Celsius and a minimum of 0 degrees Celsius (0-(15-20 degrees Celsius) ; found in cold environments

Mesophile

Midrange temperatures, most commonly studied

Thermophiles

Growth temperature optima between 45 degrees Celsius and 80 degrees Celisus ; found in hot environments

Hyperthermophiles

Organisms with optima greater than 80 degrees Celsius; found in extremely hot habitats such as hot springs and deep-sea hydrothermal vents

Extremophiles

Organisms that grow under very hot or very cold conditions

Psychrotolerant

Organisms that can grow at 0 degrees Celsius but have optima of 20 degrees Celsius to 40 degrees Celsius.