chapter 5 Brock Flashcards
Define microbial growth
an increase in cell numbers.
the final result of of the doubling of all cell components prior to actual division that yields two daughter cells.
most microorg. grow by binary fission.
binary fission is…
cell division following enlargement of a cell to twice its minimum size
biofilm
an attached polysaccharide matrix containing bacterial cells
bacteriocidal agent
an agent that kills bacteria
bacteriostatic agent
an agent that inhibits bacterial growth
divisome
a complex of proteins that directs cell division processes in prokaryotes
exponential growth
growth of a microbial population in which cell numbers double within a specific time interval
germicide (antiseptic)
a chemical agent that kills or inhibits growth of microorganisms and is sufficiently nontoxi to be applied to living tissues
halophile
a microorganism that requires NaCl for growth
halotolerant
a microorganism that does not require NaCl for growth but can grow in the presence of NaCl, often high levels
HEPA filter
a high-efficiency particulate air filter that removes particles, including microorg from intake or exhaust air flow.
hyperthermophile
a prokaryote that has a growth temperature optimum of 80 deg C or greater
mesophile
an organism that grows best at temperatures between 20 and 40 deg C
microaerophile
an aerobic organism that can grow only when O2 tensions are reduced from that present in air
minimum inhibitory concentration (MIC)
the min. conc. of a substance necessary to prevent microbial growth
neutrophile
an organism that grows best at neutral pH, between pH 5.5 and 8.
obligate anaerobe
an organism that cannot grow in the presence of O2
osmophile
an organism that grows best in the presence of high levels of solute, typically a sugar
plate count
a method of counting viable cells; the number of colonies on a plate is used as a measure of cell numbers
psychrophile
an organism with a growth temperature optimum of 15 deg C or lower and a max growth temp below 20 deg C
psychrotolerant
capable of growing at low temperatures but having an optimum above 20 deg C
sanitizer
an agent that reduces microorg to a safe level but may not eliminate them
sterilant/steriliser/sporicide
a chemical agent that destroys all forms of microbial life
sterilisation
the killing or removal of all living organisms and viruses
thermophile
an organism whose growth temperature optimum lies between 45 and 80 deg C
transpeptidation
formation of peptide crosslinks between muramic acid residues in peptidoglycan synthesis
viable
capable of reproducing
viable count
a measurement of the conc. of live cells in a pop.
xerophile
an organism that is able to live, or that lives best, in very dry environments.
What are the roles of Fts proteins in cell division and chromosome replication?
With the help of MinE, FtsZ defines the cell division plane and helps assemble the divisome, the protein complex that orchestrates cell division
What’s the role of MreB?
MreB helps define cell shape, and in rod-shaped cell walls, MreB forms a cytoskeletal coil that directs cell wall synthesis along the long axis of the cell.
What is the equivalent of MreB in Caulobacter?
Crescentin plays analogous role to MreB in Caulobacter, leading to formation of a curved cell.
How is new cell peptidoglycan synthesised during bacterial cell growth?
by the insertion of new glycan tetrapeptide units into preexisting peptidoglycan.
Bactoprenol facilitates transport of these units through the cytoplasmic membrane.
Transpeptidation completes the process of cell wall synthesis by cross-linking adjacent ribbons of peptidoglycan at muramic acid residues.
Typical microorganism growth pattern?
When inoculated into a fresh culture medium:
lag phase, exponential growth, [essential nutrients depleted & toxic products build up] growth ceases and population is in stationary phase. Further incubation can lead to cell death.
What’s a chemostat?
An open system used to maintain cell populations in exponential growth for extended periods [controls the dilution of culture with fresh culture medium, and conc. of growth limiting nutrients dissolved in medium]
When do we use counting chambers?
Microscopic counts measure the total no. of cells in a sample - good for assessing the total cell numbers in a microbial habitat.
Are viable cell counts (plate counts) accurate?
They measure only the living population present in the sample with the assumption that each colony originates from the growth and division of a single cell. Depending on the growth medium and conditions used, can be fairly accurate or highly unreliable. Repeats?
Are turbidity measurements useful?
Indirect, very rapid way of measuring microbial growth. Need to establish a standard curve of turbidity value and direct cell number first, for comparison of samples.
Abiotic factors affecting microbial growth?
Temperature;
pH;
water;
oxygen
Some of those funny -phile names please!
Psychrophiles - opt below 20 deg C Thermophiles - opt between 45 and 80 deg C Hyperthermophiles - opt above 80 deg C Acidophiles - opt low pH Alkaliphiles - opt high pH
