3. Microbial Growth

N= N₀ x 2ⁿ

• N= final cell number
• N₀ = initial cell number
• n = number of generations

g = t/n

t = time elapsed during exponential growth

• closed system of a fixed volume where bacterial growth alter environment
• 1) lag phase
• 2) log phase
• 3) stationary phase
• 4) death phase

• when a stationary phase culture is diluted into fresh medium or when cells transferred from rich to minimal medium
• must synthesize proteins for rapid growth or specific proteins needed to produce nutrients not in culture medium

• growth is limited
• run out of essential nutrient or accumulate toxic waste product
• no net change in cell number
• some processes can continue
• sigma s protein controls response to stresses

open system maintained in chemically constant environment

• dilution rate = fraction of volume replaced per time
• too fast - culture washes out, cell division can't keep up
• too slow - nutrient isn't supplied fast enough

• increase nutrient concentration - growth rate and yield affected, then only yield affected
• total yield determined by most limiting nutrient

contains complex organic molecules

contains precise amounts of known chemicals

• can get all of the C they need to build structures from CO₂
• can gain energy from photons or by oxidizing inorganic compounds

• require an organic C source
• most use NH₃- or NO₃- as nitrogen source
• only nitrogen-fixing bacteria can use N₂

must use O₂ as an electron receptor in respiration

must avoid O₂

can use O₂ in respiration or use other metabolic strategies

require low O₂ concentration

• ignore O₂
• only ferment

• cause cell damage
• superoxide radical union
• hydrogen peroxide
• hydroxyl radical

• enzymes remove toxic oxygen species
• superoxide dismutase
• catalase
• peroxidase

• critical enzymes are denatured
• membranes too fluid and cannot maintain barrier

• proteins are more stable because contain fewer glycine residues and N-termini H-bonded to rest of protein
• synthesize chaperones to refold
• synthesize phospholipids with saturated fatty acids, pack tightly to form membrane

• not much thermal motion, perform reactions slow
• membrane fluidity decreases, inhibits function of critical proteins

• proteins are more flexible
• phospholipids with highly unsaturated fatty acids, remain mobile

• water enters the cell
• bacteria have rigid cell walls, prevent lysis
• mechanosensitive channels can leak specific solutes out

• water exits the cell
• can synthesize/import compatible solutes

small molecules or ions that do not disrupt cell metabolism, increase internal osmolarity, help retain water

• bacteria that require high NaCl concentration for growth
• proteins adapted because use K+ as compatible solute

• membranes are more impermeant to protons
• ether-linked lipids are less leaky and more resistant to acid hydrolysis

expend energy to scavenge protons from environment using Na+/H+ antiporters, use membrane gradient of Na+ to drive flagellar rotation, nutrient uptake because H+ is limiting