6. microbial growth Flashcards
this is the orderly increase in the sum of all the components of an organism
growth
the survival of any microbial group within an environmental niche is ultimately influenced by successful competition for ___________
nutrients
what are the two ways microbial growth can be measured by?
- cells concentration (the number of viable cells per unit volume)
- biomass concentration (dry weight of cells per unit volume of culture)
this is typically considered the measure of cell concentration; this is done by serial dilution
viable cell count
T/F: dead bacteria within the suspension do not contribute to the final bacterial count
true \
what is the equation used to find the # of colony forming units
CFU/mL = (no. of colonies x dilution factor)/ volume of culture plate
is the stepwise dilution of a substance in solution; used to calculate the concentration of microorganisms
serial dilution
this can be measured using a spectrophotometer; it is based on the fact that microbial cells scatter light striking them. the amount of scattering is directly proportional to the biomass of the cells
turbidity
this can be measured directly by determining the dry weight of a microbial culture after it has been washed with distilled water; it can also be estimated indirectly by measuring an important cellular component such as protein, DNA or pigment
biomass
when microorganisms are cultivated in liquid medium (closed system), they are grown in _________ where there is no fresh medium provided during incubation, nutrient concentration declines and the concentration of waste decreases
batch culture
the growth of bacteria can be plotted as the log of the number of viable cells vs the incubation time which is known as
the growth curve
what are the 4 phases of the growth curve
- lag phase
- log (exponential growth) phase
- stationary phase
- decline (death) phase
this phase of the growth curve is where the cells adapt to their new environment. the cells synthesize new components, enzymes and proteins to a limit that permits growth to resume. cell division DOES NOT occur in this phase
lag phase
this phase of the growth curve is where microorganisms are growing and dividing at the maximal rate. this continues until either nutrients in the medium become exhausted or toxic metabolic products accumulate and inhibit growth
the log phase
this phase of the growth curve is the exhaustion of nutrients and the accumulation of toxic products. there is a slow loss of cells through death, which is balanced but the formation of cells through growth
the stationary phase
this phase of the growth curve is when cell viability begins to decrease at a defined rate due to the nutrient deprivation and build up of toxic waste. the death rate increases until it reaches a steady level. after the majority of the cells have died, a small number of survivors may persist for months, even years
the decline phase
after the death phase of the growth curve, as some bacteria form spores as a survival mechanism, others can become dormant without changes in morphology, and show a _____________ phenomenon which is when these cells will not grow again in a culture, but may grow and cause disease if get inside an animal
viable but not cultural (VBNC)
in some bacteria, after the death phase, some microbes have a long period where the population size remains more or less constant. during this time, the persistent cells are those best able to use the nutrients released by the dying cell, and best able to tolerate the accumulated toxins. this phase is called:
the long-term stationary phase - can last for months or years
these are complex, slime0encased communities of microbes; they are ubiquitous in nature (seen as layers of slime on rocks, plaque on teeth); a single bacterium nucleating on a surface followed by cell division and ultimately to the formation of an intimate community called:
biofilm
the biofilm surrounds itself with ____________ for environmental protection and to keep the biofilm community intact
extracellular matrix (ECM) or glycocalyx
this is the process of propagating organisms by providing the proper environmental conditions
bacterial cultivation
what are the main elements associated with bacterial cultivation
CHNOPS
