MCB3020 Week 3: Growth & Nutrition

Nutrients

Supply of monomers required by cells for growth, with some macronutrients being required in large amounts and some micronutrients being required in small amounts.

Cell dry weight

Carbon, oxygen, nitrogen, hydrogen, phosphorous, sulfur, selenium.

Carbon

Required by all cells where heterotrophs get this from organic sources and autotrophs get this from inorganic sources

Nitrogen

Key element in proteins, nucleic acids

Phosphorous

Required by cell for synthesis of nucleic acids and phospholipids

Sulfur

Plays structural role in S-containing amino acids and is present in several vitamins and coenzyme A

Potassium

Required by enzymes for activity

Magnesium

Stabilizes ribosomes, membranes, and nucleic acids, as well as being required for many enzymes

Calcium

Stabilizes cell walls in microbes and plays key role in heat stability of endospores

Sodium

Required by some microbes, particularly marine microbes

Iron

Major role in cellular respiration, ferrous soluble form under anoxic conditions, ferric insoluble form under oxic conditions

Siderophores

Produced by cells to obtain iron from insoluble mineral form

Growth factors

Free-floating structures around the cell to do the job of growing cells

Culture media

Nutrient solutions (food) used to grow microbes in the lab

Defined media

Cell is fed an exact diet

Complex media

Cell is fed a little of everything

Selective media

Used to kill some cells in a culture but not all

Differential media

In cultures with more than one cell, dye is used to tell them apart

Pure culture

Culture with only one kind of microbe

Binary fission

Cell division happens by the cell growing twice it’s size then dividing

Generation time

Time needed for cell population to double, depending on nutritional factors, genetic factors, and temperature. Difference in nature compared to the lab due to having limited resources and competition

Budding

Cell division happens by unequal cell growth by elongating, growing a bud, then splitting off into a new cell

Biofilms

Group of planktonic cells attach to a surface where they build a polysaccharide matrix. Very resistant to chemicals, antibiotics, abrasion, and grazers. Found on toothbrushes, implanted medical devices, and in cystic fibrosis

Exponential cell growth

N = N02^n where N = final cell number, N0 = initial cell number, n = number of generations during the period of exponential growth

Generation time

Exponential growing populations g = t/n where t = duration of exponential growth, n = number of generations during the period of exponential growth.

Exponential cell growth

N = N02^n can also be expressed as n = 3.3(log N – log N0)

Specific growth rate

(k) rate at which the population is growing at any instant, dN/dt=kN

Division rate

(v) or v=1/g which gives the number of divisions per unit time (ex. Per hour)

Batch culture

Closed-system microbial culture of fixed volume that has four phases; lag, exponential, stationary, and death.

Lag phase

Interval of time between when a culture is inoculated and when growth begins

Exponential phase

Cells in this phase are in the healthiest state

Stationary phase

Net growth of population is zero; one divides and one dies

Death phase

An essential nutrient is used up or waste product of the organism accumulates, exponential

Continuous culture

Open-system microbial culture of fixed volume, where a chemostat is used commonly

Dilution rate

Rate at which a fresh medium is pumped in and spent medium pumped out

Microbial growth

Measured by using microscopic counts, viable cell counting, or turbidimetric methods

Microscopic counts

Number of microbial cells is counted by hand but yields unreliable results, as live and dead cells cannot be differentiated, small cells are hard to see, precision inaccurate, stain needed.

Viable cell counts

Measurement of living, reproducing populations of cells, done with either the spread-plate method, serial dilutions, or the pour-plate method

Pour-plate method

Viable count method where sample is pipetted into plate, sterile medium is added and solidified, surface and subsurface colonies visible. More accurate than spread plates but have lower counts due to the heated agar

Serial dilution

Viable count method where 1mL of broth is placed into a tube of water, where that tube of water then has 1mL taken from it into a new tube of water and the cycle continues down. The number of colonies lessens and becomes easier to count. The number of colonies counted is multiplied by the dilution factor to find the cells per millimeter of original sample.

The Great Plate Anomaly

Direct microscopic counts of natural samples typically reveal far more organisms than are recoverable on plates of any given culture medium due to microscopic methods counting dead cells as well as live ones, and different organisms in even a very small sample may have very different requirements for resources and conditions in a laboratory culture.

Cardinal temperatures

Minium, optimum, and maximum temperatures at which an organism grows. Minimum and maximum growth aren’t possible, but optimum growth is the most rapid

Psychrophile

Microorganism grows best in low temperatures, found in permanently cold environments where less than 15 C but higher than 0 C is the most optimal

Mesophile

Microorganisms grow best in midrange temperatures, found in warm-blooded animals, terrestrial and aquatic environments, temperate and tropical latitudes. Ex. E. coli

Thermophile

Microorganisms grow best in high temperatures, optimal growth temperature ranges 45C-80C

Hyperthermophile

Microorganisms grow best in very high temperatures, optimal growth temperature is above 80C with archaea being above 100C and bacteria being about 95C. Found in boiling hot springs and seafloor hydrothermal vents. Chemoorganotrophic and chemolithotrophic species present. They also produce enzymes that are widely used in industrial microbiology

Extremophile

Organisms that have evolved to grow optimally under very hot or very cold conditions

Psychrotolerant

Organisms that can grow at 0 C, but optima range 20C-40C and is more widely distributed in nature than psychrophiles

Growth

Some other environmental factors impacting cell’s _ are microbial growth at low or high pH, osmotic effects on microbial growth, oxygen and microbial growth, toxic forms of oxygen

Neutrophiles

Most organisms grow best at pH 6 to 8

Acidophiles

Organisms grow best below pH 6, with some being obligate due to their membrane being destroyed at a neutral pH. Stability of the cytoplasmic membrane is critical

Alkaliphiles

Organisms grow best above pH 9, with some having a sodium motive force alongside the proton motive force

Halophiles

Organisms grow best at reduced water potential and have a specific requirement for NaCl

Extreme halophiles

Organisms that require high levels of (15-30%) of NaCl for growth

Halotolerant

Organisms can tolerate some reduction in water activity of environment, but generally grow best in the absence of the added solute NaCl

Aerobes

Requires oxygen to live

Facultative organisms

Can live with or without oxygen

Aerotolerant anaerobes

Can tolerate oxygen and grow in its presence even though they cannot use oxygen

Microaerophiles

Can use oxygen only when it is present a level reduced from that in air

Anaerobes

Does not require oxygen and may even be killed by exposure

Toxic forms of oxygen

Can be formed by cell processes such as reducing O2 to water, and includes O, O2-, H2O2, and OH radical

Vitamins

Most required growth factors where most function as coenzymes

Coenzymes

Works alongside the main enzyme

Turbidity

Measurements that are an indirect but very rapid and useful method of measuring microbial growth