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BIO 220

4. Microbial Growth(From Brock Chapter 6)

Growth is defined as an increase in the number of cells. Prokaryotes do not undergo mitosis, but instead

employ a process called Binary Fission. Cellular division is characterized by an increase in biosynthesisreactions.

Growth Rate =

Generation Time = Doubling TimeTime required for 1 cell to divide into 2

Grow proportionally = in balanced growth

Binary FissionCell elongation, DNA replication, formation of septum (cell membrane), pinching off of cell membrane andcell wall, 2 daughter cells arise.

Fts Proteins and the cell division planeFts- Filamentous temp sensitive (cells w/ mutations for coding Fts proteins, form filamentous cells

that fail to divide)FtsZ, key Fts prot, imp in cell div, all proks

Found in all proks (mostly Bact), Mito, ChloroFts prot sim in structure to tubulin, imp cell-div prot in euks

Fts prot polymerize into ring (will be cell-div plane), recruit enzymes involved in mem (ZipAanchors, FtsA too+recruits)and cell wall synth (FtsI=penic-bind prot, for prptido synth) -(after elong +repl begins) Divisome, thendivision septum =new mem,wall material

before nucleoids sep, they block form ofFtsZ ringpg 120, 151

-filam temp sens-in all mini-Fts like tubulin-Divisome: Fts ring, enzymes in mem+wall synth

Cell shape and the role of MreBMreB forms an actin-like cytoskeleton (spiral bands) in proksFilamentous, spiral shaped polymer just underneath the cell membrane.Cells lacking the MreB gene are cocci shaped.

-MreB like actin

Peptidoglycan synthesis and cell divisionCell wall elongation involves simultaneous cutting of peptidoglycan and insertion of new

peptidoglycan units. Subunits are shuttled across cell membrane by hydrophobic compoundBactoprenol.

Transglycosylation - N acetylglucosamine, N acetylmuramic acid moieties are added to glycanlayers surrounding cell.

Transpeptidation- formation of peptide crosslinks between muramic acid residues in adjacentglycan chains- solidifies the new cell wall structure.

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Time

# of cells (or mass)

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Growth CurveApplies to populations not individual cellsSee board

A = Lag PhaseB = Exponential Growth Phase (log phase)C = Stationary Phase

D = Death Phase

Why is growth not instantaneous?

Lag:Cellular repairRe-synthesis of cellular enzymes

Over 2000 chemical reactions taking place

Exponential Growth (logarithmic growth):Constant growth rateAside: competent cells vs. DNA isolation

Stationary Phase:Limiting nutrients, O2, H20, Carbon source, Nitrogen SourceAccumulating wastesSurvival genes expressed

Death Phase:# of dying cells exceeds # of new cellsGlycocalyx may aid in survivalSpore formation

Factors Affecting Growth:Available nutrients

TemperatureOxygen concentration

Acidity/alkalinity (pH)SalinityGenetics

Measurement of GrowthTurbidityDirect microscopic countViable countDry weightOxygen uptake

TurbidityAs bacteria grow culture becomes cloudyMeasure turbidity using photometer or spectrophotometerDisadvantage: dead cells counted

Loss of accuracy at high turbidityAdvantage; quick, easy, no loss of sample

Direct Microscopic CountPlace cells on slide, dry them and countCounting chamber

Chamber of grids under glassPrecise volume to each squareCount provides # cells/volumeDisadvantage: dead cells counted

Precision must be goodUnseen cells are not counted

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Viable CountPlate count or colony countAccomplished via spread plate or pour plateUses serial dilutionsAdvantage: counts only living cellsDisadvantage: requires accurate plating and good dilution technique

2 cells may form one colony if close enough together

Not all cells develop at same rate (mixed culture)

Industrial app: Food Industry, dairy industry

Continuous CultureChemostat

Permits control of both population density and growth rateUtilizes: Dilutions of cells

Limiting nutrients

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