Micro test 2 BIO 303 Liberty University

Cell cycle

The complete sequence of events extending from formation of a new cell through the next cell division.

Three phases:

Three phases of cell cycle/ binary fission

•Period of growth after the cell is born.

•Chromosome replication and partitioning.

•Cytokinesis, during which a septum and daughter cells are formed.

•Most bacterial and archaeal cells reproduce by .

binary fission

Some bacteria reproduce by forming a --- or -----

bud, multiple fission

Bacteria and Archaea can only undergo

Asexual reproduction

Most bacteria undergo

Binary fission.

In what process does the mother cell remains same size, bud grows on side of cell / Mother cell can have distinct properties than daughter cells

budding

Eukaryotes can undergo

sexual and asexual reproduction

Asexual reproduction in eukaryotes

Binary fission

Budding

Multiple fission

Fragmentation

Multiple fission

Mother cell produce many daughter nuclei (nucleus divides). Become multiple daughter cells after repeated cellular divisions

Fragmentation

- part of a multicellular/colonial organism breaks off and starts a new organism

Sexual reproduction in eukaryotes

meiosis (diploid → haploid → diploid (zygote - fusion of gametes))

Bacterial cells grow ----

exponentially

generation time

•Time required for population to double

•Varies among species and dependent on environmental conditions

Nt = N0 x 2n

(Nt ) final number of cells in population at specific time

(N0 ) starting number of cells in population

(n) number of generations

•Rapid generation time with ------- can yield huge populations quickly

optimal conditions

A typical growth curve occurs in a ------ and is characterized by five stages

batch culture/closed system

What are the five stages of a typical growth curve

Lag phase

Exponential phase

Stationary phase

Death phase

Long-term stationary phase

What happens in the lag phase.

•Initial phase, the number of cells does not increase

•Synthesize enzymes required for growth

•Length of time depends on nutrient availability and complexity

What happens in the exponential phase.

•Cells divide at constant rate

•Population doubles with each generation

•Maintain primary metabolites

•Most susceptible to antibiotics during this phase

•Cells enter late log phase when nutrients become limiting = increased competition

•Synthesize secondary metabolites

what is a primary metabolite

•Compounds required for growth

Why are bacteria susceptible to antibiotics during exponential phase.

•Most antibiotics target enzymes for metabolism & reproduction

Secondary metabolites

•Used to enhance survival via competition

•Ex: Antibiotics

What is stress induced in the late log phase.

sporulation in Endospore-formers

Stationary phase

•Nutrient levels low, cannot sustain exponential growth

•Total numbers remain constant

•Balance between cell division and cell death.

Death phase

•Decrease in viable cell count

•Nutrients very limiting

•Waste (toxic) increasing

Phase of prolonged decline / Long term stationary phase

•Remaining ~1% cells enter prolonged decline

Persistence phenotype

very low metabolic activity

What determine bacterial growth

environmental conditions

•In nature, most bacteria live in ------

multicellular associations

•Biofilms

Cause slipperiness of rocks in stream beds, slimy "gunk" in sink drains, scum in toilet bowls, dental plaque

Another multicellular association

•Swarms/fruiting bodies

Myxobacteria (slime bacteria) use gliding motility to form ------ (social motility) of cells that move over moist surfaces as a pack

swarms

Benefits to aggregation (swarm)

Collectively release enzymes and degrade organic material, including other bacterial cells

When water or nutrients become limiting, cells form protective fruiting body visible to naked eye

When water or nutrients become limiting, cells form ------ visible to naked eye

protective fruiting body

sessile

attached to surfaces

planktonic

free floating

biofilm

complex, slime enclosed communities of microbes

Extracellular Polymeric Substances (EPS)

a self-produced matrix used by a group of cells to stick to each other and adhere to a surface.

Formation of Biofilm

•Free-moving bacteria (Planktonic) adhere to an environmental surface

•Density increases (binary fission, other cells attach) - form microcolonies

•Secrete and communicate via chemical signals (autoinducers) - quorum sensing

Quorum sensing

•Cells communicate density with one another via chemical signals (autoinducers)

•In order to conduct business, a sufficient number of microbes must be present and participating.

•When a certain threshold is reached, this triggers changes in gene expression

•N-acylhomoserine lactone (AHL)

The autoinducer molecule that diffuses into and out of cells, thereby permitting an assessment of population density.

Phenotypic changes as a result of quorum sensing:

•Cells produce fimbriae to attach to substrate and each other

•Cells produce slimy extracellular matrix of proteins, polysaccharides, and nucleic acids (EPS)

•nutrients and oxygen in biofilm -----

deplete

Cells in outer layers detach and become ------

planktonic

•Biofilm Characteristics

•Most often composed of multiple species

•Channels present where nutrients and waste flow through

•Cells within a biofilm are phenotypically different than planktonic cells

Benefits of biofilm

•EPS provides protection from toxic compounds (antibiotics & disinfectants) and predation (phagocytes)

•Increased horizontal gene transfer (sharing genes)

Biofilms can cause chronic infections because

1.Poor penetration of antibiotics

2.Phagocytosis reduced

3.Resistant phenotype - because of limiting nutrients in older biofilms (ex: endospores)

4.Persistence phenotype - microbes in older biofilms that adopt a highly protected state = very low metabolic activity

5.Altered microenvironment - ex: changes in pH may affect antibiotic effectiveness

•Violacein

- Secondary metabolite produced in the presence of quorum sensing molecules (autoinducers) at high population densities (biofilm)

Biofilms have ------ properties because of the ------ produced

antifungal, violacein

Mutualism

A relationship between two species in which both species benefit

Syntropy

some bacteria live together and supply each other with essential nutrients.

The ----- of one organism feeds another

waste

Competitive interactions

•Secrete toxic compounds to inhibit competitors

•Some Gram-negative bacteria use syringe-like structures (Type VI secretion system) to inject toxic compounds (effector proteins) directly into competing bacteria

Robert Koch

•Developed solid culture media

•First used gelatin (low melting temp) to solidify nutrient broth

Fannie Hess

suggested agar she used to harden jelly

History of growing bacteria in culture

•Mixed/Mass culture common in early days of bacteriology

•Liquid broth media was common -> nearly impossible to isolate individual cells

•There was a great need for a pure culture

•Culture medium

—solid or liquid mixture of nutrients and other compounds.

Knowing the necessary growth requirements allows us to culture organisms on --------

labratory media

two types of laboratory cultivation

1.(Chemically) Defined

2.Complex

Chemically-defined media

•Composed of exact amounts of pure chemicals

•Used for research experiments

•Allows microbiologists to determine the exact nutrients required by a particular microorganism

Complex (undefined) media

•Exact chemical composition of ingredients of culture medium is unknown

•Practical for routine culture maintenance because very easy to make

The unique culture media used to detect/isolate particular microbes

•Selective media

•Differential media

Selective media

•Inhibits growth of certain organisms

Media type with antibiotics

•MacConkey agar

type of selective media

•Inhibits G+

•Allows G- enterics (e.g., E. coli) to grow

Differential media

•Usually causes some kind of color change to identify bacteria based on metabolism/phenotypic differences

•MacConkey agar contains

Lactose fermenters

•Fermentation → acid → pH, indicator (neutral red) changes color

•Blood agar

Differentiates between Hemolytic versus nonhemolytic bacteria

•Hemolysin lyses red blood cells

zones in blood agar

•Beta hemolysis = clear zone

•Alpha hemolysis = small partial cleared zone

•Gamma hemolysis = no hemolysis

Anaerobes

die in prescence of oxygen, must be grown in anaerobe jar which converts Oxygen into water

anaerobic chamber

An enclosed compartment maintained in an anaerobic environment; a special port is used to add or remove items

batch culture

•Prokaryotes grown on agar plates or in tubes or flasks of broth

Closed system

•Nutrients not renewed; wastes not removed

•Because of closed system, yields characteristic growth curve

•continuous culture

•Nutrients continuously added and waste removed

•Maintains microbes at exponential phase of growth

Growth curve for colonies on agar media

Very similar to broth, but...

------- within colony affects

nutrient availability

position

Cells at ---- of colony have more oxygen and nutrient availability

edge

Cells at ------ have higher competition, depleted nutrients/O2, wastes accumulate

center

Cultures can grow from a

•single prokaryotic cell

On solid media via binary fission, 1 cell can form 1 visible -------

colony = a visible mass of cells

Pure culture

population of cells derived from a single cell

------ of bacteria can be cultured with current techniques

•~1-10%

Goal of streak for isolation

Obtain pure culture, each successive streak decreases number of cells.

All colonies in streak for isolation have the same

morphotype = derived from single cell

T or F Prokaryotes can be extremeophiles

T

Major ababiotic factors that influence growth

•Temperature

•Oxygen

•pH

•Water availability

the temperature that has the highest growth rate

optimum growth temperature

T or F Microbes are divided into 6 categories based on optimum growth temperatures

F, 5

•Psychrophiles

-20°C to 15°C

•Prevent ice formation in cytoplasm using antifreeze proteins

White nose syndrome

•Psychrotrophs

0°C to 30°C

•Think food spoilage - opt. at RT but still grows in fridge

•Mesophiles

25°C to 45°C

Associated with humans (37 ° C) and other animals (mutualist - pathogen)

Thermophiles

45°C to 70°C

•Hot springs

•Hyperthermophiles

70°C to 110°C

•Most are Archaea

•Deep-sea hydrothermal vents

•Proteins of (hyper)thermophiles resist

denaturing

•Thermostability of hyperthermophiles comes from

amino acid sequence

•Refrigeration (~4°C) slows spoilage by limiting growth of otherwise fast-growing ----------

mesophiles

•Freezing preserves food; however it is not

effective at killing microbes

•Mycobacterium leprae

Hansen's disease (leprosy) in coolest regions (ears, hands, feet, fingers) due to lower thermal optimum

Treponema pallidum

(syphilis) - Plasmodium (malaria) used to treat by inducing fever (1920-1940) = pyrotherapy

Temperature varies among body regions, therefore

•Some microbes only cause disease in certain parts

•Temperature can influence phenotypic traits (------------)

gene expression