W3 Growth and Physiology Flashcards
what happens during lag phase of the growth curve
when cells do not immediately divide when inoculated in a fresh medium
cells may become larger and more active while they gear up for cell division
older cultures have longer lag phases > exponential cells usually do not have a lag phase in new culture
what happens during exponential growth in the growth curve
when cells are undergoing a constant and maximal growth rate in the given conditions
what happens during stationary phase of the growth curve
phase after exponential phase where cells are alive but not growing
cells often become smaller; reduce number of ribosomes
induction of genes for survival and maintenance
sporulation increases (starvation)
what is stationary phase caused by
substrate limitation
O2 limitation due to high respiration rates and low solubility of O2
toxins (waste products)
NOT due to cell crowding
definition of cryptic growth
where death = growth rate
what happens during death phase of growth curve
decline in cell numbers highly variable and not predictable by any mathematical relationship
may be linear or exponential
sometimes accompanied by cell lysis
measurements of microbial growth
direct count: cells counted under special microscopic slide
viable plate counts: small sample of cells spreader on agar plates and incubated
turbidimetric: culture tube is measured in spectrophotometer for turbidity
other indirect methods: O2 consumption, CO2 production, ATPase
how does direct count work
fastest method and very accurate
usually stain cells
dead cells are counted
how does viable plate count work
sample pipetted onto surface of agar plate > spread evenly over surface of agar
assumes that single cell will divide and after a suitable incubation period > give rise to single colony forming unit (CFU)
how does turbidimetric work
indirect method using spectrophotometer
detect cloudiness
more cells > more light scattered > less light detected
what are aerobes
obligate: requires O2 for growth
microaerophile: grow with O2 at levels less than atmospheric
what are anaerobes
obligate: grow only in absence of O2 by anaerobic respiration or fermentation; killed by O2
aerotolerant: grow by fermentation in the presence of O2 but can not use it
facultative: grow with O2 but can also grow using inorganic electron acceptors and/or by fermentation
how do microbes adapt to low nutrients
become more competitive in nutrient capture and use of available resources
morphological changes to increase surface area and ability to absorb nutrients
mechanisms to sequester certain nutrients
what are extremophiles
microorganisms that grow under harsh conditions that would kill most organisms
most are prokaryotes
still have ranged below or above which they will not grow
environmental factors and their ranges
temperature: from -36 degrees to 122 degrees
pH: 0 to 11.5
osmotic effects: from pure water to 30% NaCl
O2: with or without
high pressure: occurs in deep sea and called barophiles
radiation: 3 to 6 mega million rads
