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#bacterial growth curve

7 public questions tagged with this topic.

Microbial Physiology

What is the primary reason for bacterial death in the death phase?

Transition to death phase reflects inability to maintain energy homeostasis and repair. Prolonged incubation exhausts fermentable carbon, electron acceptors, phosphate, amino acids, halting ATP generation via respiration and substrate level phosphorylation. Concomitantly toxic end products accumulate: organic acids acetate and lactate lower pH below 5, alcohols ethanol, ammonia, hydrogen sulfide inhibit cytochrome oxidases, and reactive oxygen species superoxide and H2O2 from autooxidation damage iron sulfur clusters. Oxidative lesions cause DNA strand breaks, protein carbonylation, membrane l

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Death phase - Toxic metabolites accumulation.

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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

Which phase is characterized by exponential bacterial growth?

Log phase also termed exponential phase represents balanced growth state where every cellular constituent doubles at identical specific rate. Under saturating nutrients and aeration, DNA replication initiates synchronously via DnaA ATP activation at oriC, elongation by PolIII, segregation by MukBEF SMC complex, and cytokinetic ring FtsZ with FtsA ZipA divides cells with constant interdivision time. Specific growth rate mu maximal, defined by mu equals ln2 over generation time g. Equation dN over dt equals mu N integrated yields N equals N0 times e to mu t, producing straight line on semi-log p

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Exponential phase and balanced growth.

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Microbial Physiology

In which phase of the bacterial growth curve do bacteria adapt to their environment?

After transfer to fresh medium, cells display temporarily static numbers while metabolic machinery adapts, called lag phase. Stationary phase inoculum carries oxidative damage, aggregated proteins, low rRNA pool, condensed nucleoids, and altered membrane fatty acids. Cells sense new environment via two component systems PhoP PhoQ, EnvZ OmpR, induce specific sugar transporters, amino acid biosynthesis operons, and pentose phosphate pathway to generate NADPH. Ribosomal RNA operons rrn rapidly upregulated, increasing ribosome content, tRNAs charged, ATP pools rebuilt via substrate level phosphory

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 6: Lag phase adaptation.

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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

Which of the following occurs in the stationary phase of bacterial growth?

When batch cultures exhaust carbon, nitrogen or phosphate and accumulate organic acids like acetate lowering pH, growth rate decelerates and matches death rate producing plateau termed stationary phase. This phase triggers global reprogramming governed by alternative sigma factor sigmaS encoded by rpoS in Escherichia coli and master regulator Spo0A in Bacillus subtilis. Cells activate stringent response via RelA sensing uncharged tRNA and SpoT synthesizing alarmones ppGpp and pppGpp which inhibit stable RNA promoters and redirect transcription to survival genes. Adaptations include highly resi

Ref: Prescott's Microbiology, 11th ed., Chapter 6: Stationary Phase, Sporulation and Secondary Metabolites.

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Microbial Physiology

Which phase of the bacterial growth curve is also known as the acclimatization phase?

Batch growth exhibits four phases in closed culture: lag, log, stationary and death. Lag phase immediately after inoculation into fresh medium appears flat by cell number but represents highly active metabolic acclimatization. Cells sense new nutrient composition, pH, osmolarity and oxygen via EnvZ-OmpR and chemoreceptors, induce necessary transporters and catabolic operons such as lac when lactose present, repair oxidative damage accumulated in stationary-phase inoculum via base excision repair, and massively synthesize ribosomes, tRNAs and aminoacyl-tRNA synthetases to prepare for rapid prot

Ref: Prescott's Microbiology, 11th ed., Chapter 6: Lag Phase as Acclimatization Phase of Growth Curve.

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