#bacterial growth

Microbial Physiology

What is the optimum growth temperature for hyperthermophiles?

Hyperthermophiles are extremophiles with optimum growth temperature above eighty degrees Celsius, maximum often exceeding 100, isolated from submarine hydrothermal vents black smokers, terrestrial solfataras, geothermally heated sediments and deep oil reservoirs. Members include archaeal Pyrolobus fumarii 106 degrees, Thermococcus kodakarensis, Thermus, bacterial Thermotoga maritima, Aquifex aeolicus chemolithoautotroph. Adaptations include proteins with increased ionic networks, compact hydrophobic cores, higher charged residue proportion, reduced thermolabile asparagine glutamine, oligomeriz

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 19: Hyperthermophiles - Optimum >80°C.

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Microbial Physiology

In the log phase, bacterial cell numbers increase by a factor of:

Balanced exponential growth implies each cell divides into two, so number after one generation doubles. In log phase cultures specific growth rate constant, generation time minimal, cells divide asynchronously but average population doubling per generation time. Starting N0, after n generations N equals N0 times two to n. Therefore per generation increase factor exactly two, not one meaning no growth, nor four or eight which would imply multiple fission or formation of tetrads and octads seen in some cocci Sarcina but not typical rods Escherichia coli bacilli dividing by binary transverse fiss

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Log phase - Cell number doubles factor 2.

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Microbial Physiology

The diauxic growth curve results from the metabolism of:

Historical diauxie experiment performed by Jacques Monod in 1940s used Escherichia coli growing in mixture of glucose and lactose where total sugar limited growth. Growth curve displayed first rapid exponential on glucose, plateau slight lag, second slower exponential on lactose. Reasoning glucose metabolized via Embden Meyerhof pathway directly to pyruvate yielding ATP quickly, while lactose requires uptake via LacY permease and hydrolysis by beta-galactosidase LacZ to glucose plus galactose then Leloir pathway. Regulation ensures lac operon silent during glucose phase due to low cAMP and abs

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Section: The lac operon and diauxic glucose-lactose metabolism.

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Microbial Physiology

Which of the following is not a factor affecting bacterial growth?

Microbial growth influenced by physicochemical variables reflecting physiology. Temperature controls enzyme catalysis activation energy, membrane fluidity, protein thermostability, cardinal minima optima maxima distinct per species. Oxygen availability categorizes obligate aerobes requiring cytochrome oxidases and superoxide dismutase, obligate anaerobes lacking detoxification killed by oxygen, facultative anaerobes switching via Fnr ArcAB, microaerophiles needing low oxygen. pH affects proton motive force, amino acid charge, solubility nutrients. Water activity aw controlled by osmotic solute

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 7: Factors affecting growth - Mitochondria absent.

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Microbial Physiology

If a bacterial culture starts with 200 cells and undergoes 5 generations, how many cells will be present?

Bacterial population expansion follows geometric doubling law Nt equals N0 times two to power n where n number of generations completed. This exponential power explains rapid colonization from few cells. For inoculum 200 cells undergoing five generations calculation yields successive doublings: after one generation 400, second 800, third 1600, fourth 3200, fifth 6400 cells assuming no mortality. Therefore final yield after n generations grows quickly even with modest No. Relationship assumes balanced exponential phase, constant generation time, negligible death, typical early batch before subs

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Population formula Nt=No2^n.

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Microbial Physiology

What is the primary reason for an extended lag phase in bacterial cultures?

Extended lag phase not caused by high density per se but by requirement for extensive macromolecular synthesis before replication can resume. Cells transferred from old, stationary, or differently composed medium lack enzymes for new carbon source utilization, transport permeases, central metabolic dehydrogenases, and contain degraded ribosomes, oxidized proteins, and damaged DNA. They must induce transcription of catabolic operons lac, mal via cAMP CRP, synthesize ribosomal proteins rps, rpl, produce tRNA, generate ATP via substrate level phosphorylation, repair chromosome via Uvr, Rec system

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Extended lag - Enzyme synthesis requirement.

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Microbial Physiology

The rate of bacterial cell decline in the death phase follows:

Loss of viability after stationary eventually outweighs division, producing decline phase where total colony forming units drop. Empirical measurements show semi-log plot of survivors versus time yields linear decay, indicating constant probability of death per unit time per surviving cell, independent of absolute numbers. This defines first order kinetics analogous to chemical decomposition rate minus kd N integrated ln N equals ln No minus kd t. Decimal reduction value D equals ln10 over kd, time required for tenfold drop, used in sterilization validation. Mechanistically stochastic oxidativ

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Death kinetics - First-order decline.

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Microbial Physiology

Which equation best describes exponential bacterial growth?

Exponential increase in bacterial population when resources unlimited follows first order kinetics proportional to current population. Mathematically rate change dN over dt equals mu N, where N cell number, mu specific growth rate inverse time. Factor mu reflects nutritional quality, temperature, aeration, strain genotype. Integration yields N(t) equals N0 e to mu t, equivalently N0 2 to power t over g, where g equals ln2 over mu generation time. Taking natural logarithm ln N versus time gives straight line slope mu, confirming balanced growth. Monod equation refines mu as function substrate c

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Exponential growth equation dN/dt=μN.

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Microbial Physiology

The formula for calculating generation time (g) in bacterial growth is:

Quantitative estimation of bacterial growth uses relationship between elapsed time and number of doublings. Definition generation time g equals total incubation time t divided by number of generations n realized in that interval, g equals t over n. Generation number derived from cell counts using formula n equals log2 Nt over N0 equals log10 Nt minus log10 N0 over 0.301, where N0 initial density, Nt final. This equation derives from geometric progression Nt equals N0 times 2 to n. Therefore knowing t and n yields g, alternatively g predicts expected increase. Reciprocal relationship gives spec

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Formula for generation time g=t/n.

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Microbial Physiology

What is the generation time in bacterial growth?

Generation time defines kinetic metric of prokaryotic proliferation, interval required for population to double in cell number during balanced growth. Since bacteria propagate by binary transverse fission, each mother cell splits into two genetically identical daughters after chromosome replication, partition via ParABS, and septal wall formation by divisome. Therefore cell number doubling corresponds to one complete cell cycle. During exponential phase generation time g remains constant, specific growth rate mu equals 0.693 over g. Values vary dramatically: Vibrio natriegens fastest known 10

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Generation time and doubling.

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Microbial Physiology

Which equation best describes the exponential bacterial population growth?

Exponential growth is idealized as first-order autocatalytic process where instantaneous rate of new cell formation is proportional to existing population. Differential equation is dN/dt equals mu times N where N is cell number at time t and mu is specific growth rate per hour reflecting intrinsic replication speed. Separation and integration yields Nt equals N0 times e to power mu t giving linear relationship between ln Nt and time with slope mu during log phase representing balanced growth. During true log phase mu approximates constant as all components increase proportionally. Alternative

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 4: Exponential Growth Equation dn/dt = μN.

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Microbial Physiology

Which phase of bacterial growth is best suited for industrial fermentation?

Industrial fermentation aims to maximize volumetric productivity of biomass, recombinant proteins or primary metabolites in minimal time with reproducible quality. Log phase cells are physiologically most uniform population with high ribosome content, active glycolysis and TCA cycle, abundant ATP and NADPH and low stringent response. Enzyme systems for substrate uptake like PTS and product synthesis operate at peak specific activity providing fastest conversion per cell per hour. Transferring mid-exponential inoculum into production vessel shortens nonproductive lag phase improving batch turna

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 12: Log Phase for Industrial Fermentation and Biomass Production.

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