Practice question

Batch culture progression from exponential to stationary triggered primarily by depletion of limiting substrates and buildup of inhibitory waste. During log phase glucose, ammonium, phosphate abundant, oxygen well dissolved, growth maximal. Cells actively metabolize producing organic acids acetate via overflow metabolism, carbon dioxide, secondary metabolites that acidify medium, increase osmolarity, reduce water activity. Oxygen consumption outpaces transfer creating microaerophilic conditions, electron transport slows, proton motive force drops. Sensors RelA synthesizes ppGpp upon uncharged tRNA, SpoT monitors fatty acid starvation, activating stringent response redirecting transcription from rRNA to stress genes governed by RpoS sigma. Consequently division rate declines, cell size reduces, storage compounds polyphosphate, glycogen accumulate, ppGpp inhibits initiation. When growth limiting threshold reached, culture enters stationary where cryptic growth recycles lysed cells. This nutrient and waste governed transition explains classic growth curve shape observed in closed system without replenishment, distinguishing batch from continuous chemostat where fresh medium maintains log phase indefinitely for industrial production.