Ch. 9: Microbial Growth Flashcards
Binary fission
most common mechanism of cell replication in bacteria
FtsZ protein
directs process of cytokinesis & cell division
Z ring
anchored by FtsZ binding proteins & defines the division plane between the two daughter cells
Septum
a peptidoglycan cell wall that divides the two daughter cells
Generation time
the time between the same points of a life cycle in 2 generations
Doubling time
time it takes for a population to double through 1 round of binary fission; also called generation time in prokaryotes
Growth curve
a graph modeling # of cells in a culture over time
Culture density
defined as number of cells per unit volume
Inoculum
a small number of cells; beginning of the growth curve
Culture medium
a nutritional broth that supports growth
The lag phase
initial phase of growth curve; cells are gearing up for next phase of growth
The log phase
cells are actively dividing by binary fission & their numbers increase exponentially
- stage where bacteria are most susceptible to action of disinfectants & antibiotics that affect protein, DNA, & cell wall synthesis
Stationary phase
waste products accumulate, nutrients gradually used up, total number of live cells reaches a plateau
Death (decline) phase
number of dying cells exceeds number if dividing cells, leading to exponential decrease in total number of cells
Intrinsic growth rate
generation time under specific growth conditions (nutrients, pH, temp, etc.) is genetically determined
Persisters
these few cells are characterized by a slow metabolic rate
- medically important because they are associated with chronic infections that don’t respond to antibiotic treatment
Direct microscopic cell count
- simplest way to count bacteria
- involves transferring a known volume of a culture to a calibrated slide & counting the cells under a light microscope
Petroff-Hausser Chamber
calibrated slide used in a direct microscopic cell count
Viable cells
live cells
Viable plate count
a count of viable or live cells
Colony forming unit
results of a count usually expressed this way because more than one cell may be in the same spot
Serial dilution
process used to obtain plates with CFUs in range 30-300; process usually involves several dilution of multiples of 10 to simply calculations
Pour plate method
sample mixed in warm liquid agar & poured into sterile petri dish, mixed by swirling, solidifies and is incubated, resulting colonies counted
Spread plate method
sample poured onto solid agar, spread onto agar using sterile spreader, incubated & resulting colonies counted
Membrane filtration technique
known volumes are vacuum filtered aseptically through membrane with pore size small enough to trap microorganisms; membrane transferred to Petri plate containing appropriate growth medium; colonies counted after incubation
Most probable number (MPN) method
statistical procedure for estimating the number of viable microorganisms in a sample
Turbidity
cloudiness of a sample
Fragmentation
new cells splitting from parent filament and floating away
Budding
tip of extension swells and forms a smaller cell (the bud) that eventually detaches from parent cell
Biofilms
complex and dynamic ecosystems that form on a variety of environmental surfaces
Extracellular polymeric substances (EPS)
composes the extracellular matrix, secreted by organisms in biofilm
Planktonic cells
free floating microbial cells that live in aquatic environments
Sessile
attached to a surface
Quorum sensing
- can occur between cells of different species within a biofilm
- enables microorganisms to detect their cell density through the release & binding of small diffusible molecules called autoinducers
Autoinducers
signaling molecule produced by a bacterial cell that can modify the activity of surrounding cells
Reactive oxygen species (ROS)
highly unstable ions & molecules derived from partial reduction of oxygen that can damage virtually any macromolecule or structure with which they come in contact
Thioglycolate tube cultures
starts with autoclaved thioglycolate medium, tubes inoculated and incubated
Thioglycolate medium
contains low percentage of agar to allow motile bacteria to move throughout medium
Anaerobic jar
include chemical packs that remove oxygen and release carbon dioxide; anaerobic bacteria must be grown in these
Anaerobic chamber
an enclosed box from which all oxygen is removed; gloves seal opening in box, allowing handling of cultures inside the box
Optimum oxygen concentration
the ideal oxygen concentration for a particular microorganism
Minimum permissive oxygen concentration
lowest concentration of oxygen that allows growth
Maximum permissive oxygen concentration
highest tolerated concentration of oxygen
Peroxidase
Superoxide dismutase (SOD)
breaks down powerful superoxide anions generated by aerobic respiration
Catalase
converts hydrogen peroxide to water and oxygen
Capnophiles
bacteria that grow best in a higher concentration of CO2 and a lower concetration of oxygen
Candle jar
used to grow capnophiles
Optimum growth pH
most favorable pH for growth of an organism
Minimum growth pH
lowest pH value that an organism can tolerate
Maximum growth pH
highest pH an organism can tolerate
Neutrophiles
grow optimally as a pH within 1 or 2 pH units of the neutral pH of 7
Acidophiles
microorganisms that grow optimally as a pH less than 5.55
Alkaliphiles
microorganisms that grow best as a pH between 8.0 & 10.5
Optimum growth temperature
best temperature for microorganism to grow at; growth rates are the highest at this temp
Minimum growth temperature
lowest temp at which an organism can survive and replicate
Maximum growth temperature
highest temp at which growth can occur
Mesophiles
adapted to moderate temps, optimal growth temps ranging from 20 degrees C to 45 degrees C
Pyschrotroph
also known as psychrotolerant, prefer cooler environments, from temp of 25 degrees C to 4 degrees C
Psychrophiles
microorganisms that can grow at 0 degrees C and below, have optimum temp of 15 degrees C, don’t grow above 20 degrees C
Thermophiles
organisms that grow at optimum temps of 50 degrees C to 80 degrees C
Hyperthermophiles
Halophiles
Halotolerant
Barophiles
Enriched media
Fastidious organisms
Chemically defined medium
Complex media
Selective media
Enrichment culture
Differential media
Cytokinesis
when the cell’s cytoplasm divides
4 phases of the growth curve
- lag phase
- log phase
- stationary phase
- death phase
1st stage of formation of a biofilm
involves attachment of planktonic cells to a surface coated with a substrate
2nd stage of formation of a biofilm
attachment to substrate is reversible, cells express new phenotypes to facilitate EPS formation, transition from planktonic to sessile lifestyle
3rd stage of formation of a biofilm
growth & cell division
4th stage of formation of biofilm
biofilm develops characteristic structure
5th & final stage of formation of a biofilm
cells on periphery of biofilm revert to planktonic lifestyle, sloughing off biofilm to colonize new sites
obligate (strict) aerobes
can’t grow without an abundant supply of oxygen
obligate anaerobes
killed by oxygen
facultative anaerobes
thrive in presence of oxygen but can also grow in its absence by relying on fermentation or anaerobic respiration
aerotolerant anaerobes
indifferent to presence of oxygen; don’t use oxygen because they usually have fermentative metabolism; aren’t harmed by presence of oxygen
microaerophiles
bacteria that require a minimum level of oxygen for growth
microaerophiles
bacteria that require a minimum level of oxygen for growth
