Chapter 7

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105 Terms

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binary fission

how most bacterial and archaeal cells reproduce

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cell cycle

the complete sequence of events extending from formation of a new cell through the next cell division; has three phases

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origin of replication

site at which replication begins

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terminus

site at which replication is terminated; located opposite to the origin

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replisome

DNA synthesis machinery

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partitioning system

has three components: ParA protein, ParB protein, and parS region on chromosome

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cytokinesis

formation of two daughter cells following cell division

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septation

formation of cross wall between two daughter cells

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septation steps

  1. selection of site for septum formation

  2. assembly of Z-ring (composed of protein FtsZ)

  3. assembly of cell wall synthesizing machinery

  4. constriction of cell and septum formation

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FtsZ

involved in assembly of Z-ring, first protein to localize to the future division site, monomers polymerize, localize with Min system to establish division site at midcell

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importance of Z-ring timing

location of PtsZ polymerization mist coordinate with timing; if occurs too early, Z-ring could constrict preventing proper partitioning

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nucleoid occlusion

coordinates chromosome movement and cell separation; SlmA coats chromosome except at the replication termination region (Z-ring can form when SlmA-tagged chromosome has moved away)

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divisome formation

Process in bacterial cell division where a protein complex called the divisome assembles at the midcell, leading to the formation of a septum that divides the cell into two daughter cells. Essential for successful cell division and involves multiple proteins and regulatory factors.

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peptidoglycan synthesis scheme

Process in which N-acetylglucosamine and N-acetylmuramic acid are cross-linked by peptide bridges to form a mesh-like structure in bacterial cell walls. Inhibited by antibiotics like penicillin.

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cell shape determination

cellular location of peptidoglycan synthesis plays role in determining cell shape

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coccus shape

peptidoglycan only forms at central septum, FtsZ localization placement involved

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rod shape

elongasome (rod complex) is used; MreB is scaffold by creating filaments along cytoplasmic face of plasma membrane; growth occurs in numerous bands around cell, not at the poles

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curved shape

crescentin localizes to one side of the cell, resulting in asymmetric cell wall and vibroid shape

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sulfolobus cell cycle

similar to mitotic cell cycle; growth phase (G1) followed by DNA replication (S phase), then G2 phase, segregation of chromosomes, and cytokinesis

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segregation in sulfolobus cell cycle

occurs via use of SegA/SegB protein system that is similar to bacterial partitioning systems

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SegA

similar in structure and function to ParA

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SegB

unique to archaea but thought to function similarly to ParB

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does archaea have DNA sequences similar to parS?

there is no evidence that has been found yet

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CdvA

binds the membrane and forms a non-contractile ring at midcell

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CdvB

ring constricts to separate the daughter cells

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CdvC

recruited with CdvB to the site of division

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FtsZ

Z-ring associates with new S-layer

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is growth referring to individual cell growth or population growth?

population growth

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batch culture

incubated in a closed vessel with a single batch of medium

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lag phase

cell synthesizing new components; replenishes ribosomes and ATP, adapts to new medium/conditions, cells replicate DNA, increase in mass, and divide; first phase

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exponential phase

rate of growth and division is constant and maximal; population is most uniform in terms of chemical and physical properties during this phase; second phase

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exponential growth phase depends on…

nutrient availability; final net growth increases with the initial amount of the limiting nutrient present, then growth rate increases with nutrient concentration but saturates over time

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stationary phase

when growth eventually ceases and the total number of viable cells remains constant (balance between cell division and death); happens due to nutrient limitation, limited oxygen availability, toxic waste accumulation, or critical population density has been reached; third phase

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death phase

number of viable cells declines exponentially, with cells dying at constant rate; nutrient deprivation and buildup of toxic wastes causes irreparable harm to cells; fourth phase

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long-term stationary phase

bacterial population continually evolves; process marked by successive waves of genetically distinct variants; natural selection occurs within a single culture; fifth phase

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generation/doubling time

time required for population to double in size; varies depending on species of microorganism and environment

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growth rate constant (k)

number of generations per unit time; formula: g=1/k

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extremophiles

grow under harsh conditions that would kill most other organisms

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most microbes live in a…

hypotonic environment

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mechanosensitive (MS) channel

in plasma membrane, allows solutes to leave

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protists expel excess water via…

contractile vacuoles

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halophiles

require NaCl at a concentration above about 0.2M

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extreme halophiles

require salt concentrations between 3M and 6.2M

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osmotolerant

microorganisms that can grow over wide ranges of water activity but optimally at higher levels

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xerotolerant

microbes that withstand high solute concntrations

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acidophiles

grow best between pH 0 and 5.5

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alkaliphiles

grow best between pH 8 and 11.5

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fungi prefer an environment…

with a pH 4-6

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psychrophiles

grow best in 0-20 degrees C

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psychotrophs

grow best in 0-35 degrees C

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mesophiles

grow best in 20-45 degrees C

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thermophiles

grow best in 45-85 degrees C

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hyperthermophiles

grow best in 85-100 degrees C

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protein structure of thermophiles

stabilized by more H bonds, more proline and less flexible peptides, and chaperones aid in folding

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membrane structure of thermophiles

stabilized by more saturation, more branched and higher molecular weight, and ether linkages resistant to hydrolysis

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obligate aerobe

requires oxygen

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obligate anaerobe

usually killed in presence of oxygen

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microaerophile

requires 2-10% oxygen

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facultative anaerobes

does not require oxygen but grows better in its presence

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aerotolerant anaerobes

can grow with or without oxygen

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reactive oxygen species (ROS)

superoxide radical, hydrogen peroxide, hydroxyl radical

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how microorganisms protect against ROS

aerobes produce protective enzymes like superoxide dismutase (SOD), catalase, or peroxidase

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barotolerant

adversely affected by increased pressure, but not as severely as nontolerant organisms

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peizophilic (barophilic)

requires high pressure for growth; change membrane fatty acids to adapt to increasing pressure (lipids become more unsaturated and shorter)

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ionizing radiation

X-rays and gamma rays that cause mutations that indirectly result in death; disrupts structure of many molecules (breaks H bonds and destroys ring structures)

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Deinococcus radiodurans

endospores are resistant to ionizing radiation

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UV radiation

most lethal wavelength is 260nm because it is absorbed by DNA

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visible light

at high intensities generates singlet oxygen, a powerful oxidizing agent; carotenoid pigments protect many light-exposed microorganisms from photooxidation

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microbial environments

are complex and constantly changing; expose a microorganism to overlapping gradients of nutrients and environmental factors; contain micro-and macro-organisms

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eutrophic

nutrient rich environments

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oligotrophic

low nutrient environments

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growth arrest

when a microbe enters a stationary phase in response to starvation or stress

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sessile

microbes that grow attached to surfaces

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planktonic

microbes that grow free floating

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biofilm

complex, slime enclosed communities of microbes; ubiquitous in nature in water; can be formed on any conditioned surface

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extracellular polymeric substance (EPS)

microbes reversibly attach to conditioned surface and release polysaccharides, proteins, and DNA; additional polymers are produced as microbes reproduce and biofilm matures

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quorum sensing

bacterial cells communicate via small molecules that diffuse in the environment; requires sufficient number of microbes participating

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N-acylhomoserine lactone (AHL)

autoinducer; moves across plasma membrane from the cytoplasm to the outside of the cell; when cell population is high, AHL diffuses into the cell which induces specific gene expression

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autoinducing peptides (AIP)

in gram-positive bacteria, autoinducing short peptides

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culture medium

solid or liquid mixture of nutrients and other components; used to grow, transport, and store microorganisms in the lab; must contain all growth factors microorganisms require

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defined/synthetic medium

each ingredient can be defined with a chemical formula

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complex media

contain some ingredients of nonspecific chemical composition

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agar

sulfated polymer solidifying agent; most microorganisms cannot degrade it

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peptones

partial proteolytic digestion of protein sources

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extracts

aqueous extracts that contain amino acids, peptides, nucleotides, organic acids, vitamins, and minerals (usually beef or yeast)

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supportive media

sustain growth of many microorganisms (can be made up of tryptic soy broth and agar)

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enriched media

supportive media supplemented with special nutrients (like blood agar)

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selective media

allow growth of particular microorganisms, while inhibiting the growth of others; gram-negative bacteria can grow on bile salts while gram-positive cannot

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differential media

distinguish among different groups of microbes and even permit tentative identification of microbes based on their biological characteristics

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blood agar

distinguish between hemolytic versus nonhemolytic bacteria

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MacConkey agar

distinguish between lactose fermenters versus non-fermenters

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what are candle jars used for?

anaerobic microbe cultivation

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pure or axenic culture

population of cells arising from a single cell; allows for study of single type of microorganism in mixed culture

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enrichment culture

encourages growth of microbes with a particular characteristic, while inhibiting growth of others

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three factors considered in enrichment culture

a suitable source of microbes, nutrients that should and should not be included in the culture medium, and environmental conditions

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streak plate

technique of spreading a mixture of cells on an agar surface using an inoculating loop or swab; goal is to obtain individual cells that are separated from each other (each cell can reproduce to form a separate colony)

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spread plate

small volume of diluted mixture is transferred to center of an agar plate and spread evenly over surfaces with a sterile bend rod (dilution made by serial dilution)

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pour plate

sample is serially diluted and mixed with liquid agar which is the poured into sterile culture dishes; used when sampling heterogenous populations of microbes that might produce overgrown colonies

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culturomics

use miniature cultures and incubate in many different conditions to find the best one

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direct counts

counting chambers (special slides and cover slips with grids to facilitate counting), membrane filter technique (microbes are filtered then stained), flow cytometry (stream of cells so narrow that one cell at a time passes through the laser beam), and electronic counters (like the Coulter counter)