L2: Bacterial Growth

spread plate method

directly spread ~100uL of culture onto a plate

serial dilution

dilute original sample by several factors and plate each dilution factor

optical density

cell counting method measured by opaqueness of sample, does not distinguish between different cells and live/dead cells

colony count

grow medium on a culture plate; only counts living cells but takes time for colonies to grow

direct microscopic count

place drop of culture in counting chamber, count number of cells per grid. Can detect different cell types, cannot tell live vs. dead cells

rich/complex medium

not chemically defined medium, contains complex organic molecules

defined/minimal medium

medium with precise amounts of known chemicals

exponential growth formula

N = N0 × 2^n

batch culture

closed culture where bacterial growth depletes nutrients and alters environment

stationary phase

phase of bacterial growth where conditions in batch culture change (ex. cells run out of nutrients, cells accumulate toxic waste product) and growth is limited

lag phase

phase of bacterial growth where bacterial pause growth to settle into new environment and synthesize necessary proteins

exponential phase

phase of bacterial growth where bacteria population repeatedly doubles over a certain period of time

obligate aerobes

microbes that use O2 as a terminal electron acceptor in respiration

microaerophiles

microbes that only live in places with low O2 concentration

aerotolerant anaerobes

microbes that do not use O2 for respiration, but are not harmed by it. Growth is unaffected by presence of O2

facultative anaerobes

microbes that can use O2 as well as other metabolic strategies. Grow faster with O2

obligate anaerobes

microbes that die in presence of O2

microbial adaptations to heat: avoiding denaturation

microbes have more stable proteins containing more ionic bonding, chaperones that refold proteins, solutes that stabilize proteins

microbial adaptations to heat: membrane stability

microbial cells produce phospholipids with longer, saturated tails. They are linear and can pack tightly

microbial adaptations to cold: slow reaction rate

microbial proteins are built to be more flexible, with more gly and less ionic bonds

microbial adaptations to cold: decreased membrane fluidity

microbial cells produce phospholipids with shorter, unsaturated fatty acids. Do not pack as tightly

microbial adaptations to cold: ice crystals in cytoplasm puncture cell wall

microbial cells produce cytoprotectants to prevent ice crystal formation

microbial adaptations to external osmolarity: hypotonic medium

microbes have rigid cell walls; mechanosensitive channels leak solutes out

microbial adaptations to external osmolarity: hypertonic medium

microbes synthesize/import solutes