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#growth phases

9 public questions tagged with this topic.

Microbial Physiology

During which phase does sporulation occur in spore-forming bacteria?

Endospore formation among Firmicutes is strategy for persistence when environmental conditions deteriorate, occurring specifically upon entry to stationary phase. Triggered by nutrient limitation, high cell density quorum peptides Phr, ComX, accumulation of guanosine tetraphosphate ppGpp produced by RelA SpoT. Phosphorelay KinA to KinE autophosphorylate and transfer to Spo0F to Spo0B to Spo0A, master transcription factor. Phosphorylated Spo0A activates genes for asymmetric polar septum via SpoIIE phosphatase dephosphorylating SpoIIAA leading to FtsZ relocation. Forespore compartment trapped ch

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 7: Endospore formation during stationary phase.

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Microbial Physiology

The bacterial growth curve represents the number of live cells over time when cultured in:

Laboratory bacterial growth curve plotting viable number versus time is obtained from synchronous population in closed liquid batch culture, typically nutrient broth shaken for aeration. Solid agar shows colonies spatially separated, diffusion limited, colony counts reflect single time point not temporal kinetics. In broth, aliquots removed at intervals, optical density at 600 nm measures light scattering correlated to biomass and serial dilutions plated counting colony forming units representing live cells. Curve reveals four phases lag adaptation, log exponential where nutrients exceed Ks Mo

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Bacterial growth curve - Batch liquid culture.

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Microbial Physiology

In which growth phase do bacteria prepare for sporulation?

Sporulation is energy expensive differentiation reserved for conditions where vegetative growth cannot continue. Throughout exponential phase nutrients abundant, ribosome content high, cells divide via FtsZ divisome and elongasome MreB. As population density rises and carbon nitrogen phosphate become scarce, quorum peptides ComX CSF and nucleotide second messengers ppGpp c-di-GMP accumulate, sensed by KinA KinB KinC histidine kinases. Kinases activate phosphorelay transferring phosphate from Spo0F to Spo0B to Spo0A master regulator. Phosphorylated Spo0A binds 0A boxes activating over 120 genes

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Bacterial sporulation - Stationary phase Spo0A phosphorelay.

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