ch 7 bacterial and archaeal growth Flashcards
binary fission
type of cell decision where the cell elongates as new cell envelope material is synthesized, nucleoid must replicate and partitioned in half, septum splits cell in half
cell cycle
the complete sequence of events extending from formation of a new cell through the next cell division
3 phases:
- initial growth
- chromosome replication and partitioning
- cytokinesis, during which a septum and daughter cells are formed
origin of replication
site at which replication begins
replisome
DNA synthesizing machinery
steps of septation
process of forming a cross wall btw two daughter cells
1. selection of the site where the septum will form
2. assembly of the Z-ring, which is a polymer of the cytoskeletal protein FtsZ
3. assembly of the machinery for synthesis of peptidoglycan and other cell wall constituents
4. constriction of the cell and septum formation
divisome formation
z-ring associates discontinuously at mid-cell
FtsZ filaments attach to the plasma membrane through anchoring proteins, which also coordinate the enzymes that synthesize and remodel peptidoglycan in the developing septum
cellular growth and determination of cell shape
after the cell is born, it enters growth where a single cell increases in size
cell shape is strict and passed on through generations
some microbes change shape under certain circumstances
cocci cell shape
cellular location of peptidoglycan synthesis determines coccus shape
rod and curved cell shape
rod: elongasome - MreB is scaffolded, creates filaments along cytoplasmic face of plasma membrane; growth occurs in numerous bands around the cell, not at the poles
curved: crescentin - localized to one side of the cell, resulting in asymmetric cell wall and vibroid shape
batch culture
incubated in a closed vessel with a single batch of medium
five phases of growth
- lag phase
- exponential phase
- stationary phase
- death phase
- long-term stationary phase
lag phase
when microorganisms are introduced into fresh culture medium and no immediate increase in cell number occurs
- cells are synthesizing new components
- replenish spent materials
- adapt to new medium or conditions
exponential phase
microorganisms grow and divide at the maximal rate possible given their genetic potential, the nature of the medium, and the environmental conditions
stationary phase
in a closed system, population growth eventually ceases and the growth curve becomes horizontal
- total number of viable cells remain constant
- balance btw cell division and cell death
- bc of nutrient limitation, limited oxygen, toxic waste accumulation, critical population density reached
death phase
number of viable cells declines exponentially, with the cells dying at a constant rate
- nutrient deprivation and the buildup of toxic wastes cause irreparable harm to the cells
long-term stationary phase
bacterial population continually evolves so that actively reproducing cells are those best able to use the nutrients released by their dying brethren and best able to tolerate the accumulated toxins
- process marked by successive waves of genetically distinct variants
- natural selection occurs within a single culture
mechanosensitive channels
mechanisms to protect the cell from changing osmotic concentrations
in a hypotonic solution, the membrane stretches due to an increase in hydrostatic pressure and cellular swelling. MS channels then open and allow solute to leave, protecting the cell from bursting
osmophiles
microbes adapted to extreme hypertonic solutions
- halophiles - require presence of NaCl at a conc above 0.2M
water activity (aw)
measure of the degree of water availability
equal to the ratio of solution’s vapor pressure to that of pure water
- most grow well at 0.98
osmotolerant
microorganisms that can grow over a wide range of water activity but optimally at higher levels
xerotolerant
microbes that withstand high solute concs
- can preserve dessication
cardinal temps
minimum, optimum, and maximum growth temps
five types of relationships to O2
- obligate aerobe - requires O2
- obligate anaerobe - usually killed in presence of O2
- microaerophile - require 2 tp 10% O2
- facultative anaerobes - do not require O2 but grow better in its presence
- aerotolerant anaerobes - grow with or without O2
barotolerant
adversely affected by inc pressure, but not as severely as nontolerant organisms
barophilic
requires high pressure for growth
sunlight
major radiation source on earth
eutrophic
nutrient rich environments
oligotrophic
low nutrient environments
growth arrest
stationary phase
microbes are not actively dividing, nor are they dead
they are stressed by lack of nutrients or by deviation from optimal conditions
viable but not culturable state (VBNC)
the transient inability to grow under conditions that previously permitted routine growth
may happen after an extended time in growth arrest
persisters
have the ability to survive exposure to an antibiotic even though they do not harbor antibiotic resistance genes
characterized by low ATP levels
sessile
microbes found on surfaces
planktonic
microbes that are free floating
biofilm
slime-encased communities of microbes
found everywhere in nature
extracellular polymeric substances (EPS)
carb and nucleic acid polymers secreted by biofilm bacteria that comprise the biofilm matrix
include polysaccharides, proteins, glycoproteins, glycolipids, DNA
steps of biofilm formation
- substratum preconditioning by ambient molecules
- cell deposition
- cell adsorption
- desorption
- cell-to-cell signaling and onset of exopolymer production
- convective and diffusive transport of O2 and nutrients
- replication and growth
- secretion of polysaccharide matrix
- detachment, erosion, and sloughing
emergent properties
population has properties that could not be predicted from studying its component single cells - - biofilms - interactions occur among the attached organisms, use molecules to communicate and DNA uptake can occur
quorum sensing
the process in which bacteria monitor their own population density or the presence of other species of bacteria by sensing the levels of signal molecules
autoinducer
a small molecule that induces synthesis of the enzyme responsible for the autoinducer’s synthesis
- N-acyl homoserine lactone (AHL)
moves across the plasma membrane from the cytoplasm to the outside of the cell
when cell population is high, AHL diffuses in the cell which induces specific gene expression (virulence factors, light)
culture medium
solid or liquid mixture of nutrients and other compounds used to grow, transport, and store microorganisms
defined/synthetic medium
each ingredient can be described with a chemical formula
complex media
contain at least one ingredient of nonspecific chemical composition such as peptones, meat extract, or yeast extract
supportive media
sustain growth of many types of microorganisms
ex. tryptic soy broth, tryptic agar
enriched media
when other nutrients are added to supportive media to encourage the growth
ex. blood
selective media
allow the growth of particular microorganisms, while inhibiting the growth of others
ex. gram-negative grow on media containing bile salts or dyes, gram-positive is inhibited
differential media
distinguish among different groups of microbes and even permit tentative identification of microorganisms based on their biological characteristics
goal of streak plate
obtain individual cells that are separated from each other
why/when is a pour plate useful
when sampling a heterogeneous population of microbes, some of which might produce colonies that overgrow an agar surface if isolated by the streak or spread plate method
culturomics
use mini cultures and robotics to formulate many types of media and incubate in many different conditions to find the best one
direct counts
- counting chamber
easy, inexpensive, quick
gives info about size and morphology - membrane filter technique
microbes filtered then stained with fluorescence - flow cytometry
creates a stream of cells that one cell at a time passes through a beam of laser light - electronic counters
coulter counter - microbe suspension of forced through a small hole, counted by electrical current flow
colony forming units (CFU)
the number of microorganisms that form colonies when cultures using spread plates or pour plates, an indication of the number of viable microorganisms in a sample
membrane filter method
bacteria from aquatic samples are trapped on membranes, soaked in culture media, then grown
colony count determines number of bacteria in sample
method of measuring cell mass
dry weight - cells from liquid culture are pelleted by centrifugation and weighed
spectrophotometry - amount of scattering is directly proportional to the biomass of cell present and indirectly related to cell number
continuous culture system
method of growing microorganisms in a system with constant environmental conditions maintained by supplying nutrients and removing wastes
allow study of microbial growth at very low nutrient concs, close to those present in natural environment
chemostat
method of continuous culture system
rate of incoming medium = rate of removal of medium
most stable and effective at lower dilution rates
turbidostat
continuous culture system
regulates flow rate of media through vessel to maintain predetermined turbidity
maintains a desired cell density
dilution rate varies, contains all nutrients in excess
best at high dilution rates
