Bacterial Growth, Nutrition, and Genetics

Catabolism

breaking of chemical bonds and the release of energy.

Anabolism

formation of chemical bonds which requires energy.

Lag Phase

The period of little or no cell division which can last for 1 hour to several days. However, the cells are not dormant during this time.

Log Phase or Exponential Phase

The cells begin to divide and cellular reproduction is most active during this period, and generation time reaches a constant minimum.

Stationary Phase

The period of equilibrium. Eventually, the growth rate slows, the number of microbial deaths balances the number of new cells, and the population stabilizes.

Death Phase or Decline Phase

The number of deaths eventually exceeds the number of new cells formed. This phase continues until the population is diminished to a tiny fraction of the number of cells in the previous phase or until the population dies out entirely.

Microorganisms are also affected by several factors

availability of nutrients, moisture, temperature, pH, osmotic pressure and salinity, barometric pressure, and gaseous atmosphere.

Protoplasm’s six major chemical elements

carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

Essential nutrients

materials that organisms are unable to synthesize, but are required for the building of macromolecules and sustaining life.

Autotrophs

Use inorganic carbon (CO₂) to build cellular biomass.

Heterotrophs

Depend on organic compounds (sugars, amino acids) for carbon and carbon backbones.

Phototrophs

Harness light energy through pigments

Photoautotrophs

harness light energy to fix carbon dioxide into biomass.

Photoheterotrophs

capture light energy but rely on organic molecules for their carbon skeletons. This mixotrophic lifestyle allows them to thrive where nutrients or light are limiting.

Chemotrophs

Obtain energy by oxidizing chemical compounds.

Chemoautotrophs

Oxidize inorganic molecules (e.g., H₂, NH₃, Fe²⁺) and fix CO₂ for biomass.

Chemoheterotrophs

Oxidize organic compounds for both energy and carbon.

Obligate Aerobe

Cannot survive without oxygen

Facultative Anaerobe

Primarily aerobic but can grow in the absence of oxygen

Microaerophilic

Only aerobic growth; grow maximally at low oxygen concentration of <0.5% to 0.3%

Aerotolerant Anaerobes

Only anaerobic growth, continues growth in the presence of oxygen.

Obligate Anaerobes

Cannot live with oxygen

Capnophilic organisms

Prefer an environment with increased CO2 of 3% to 10%

Psychrophilic

Cold-loving organisms

Mesophiles

Moderate-temperature loving organisms; 25–40°C

Thermophiles

Heat-loving organisms

minimum growth temperature

lowest temperature at which organisms grow

optimum growth temperature

temperature at which organisms grow best

maximum growth temperature

highest temperature at which organisms grow

Psychroduric organisms

prefer warmer temperatures, but can tolerate or endure very cold temperatures and can be preserved in the frozen state.

pH 6.5 to 7.5

Optimum pH of most bacteria is between

Acidophiles

highly acidic environment; pH of 2 to 5

Alkalophiles

Prefer an alkaline environment; pH of 8.5

Piezophiles

thrive deep in the ocean and in oil wells, where the atmospheric pressure is very high. Some archaea, for example, are piezophiles, capable of living in the deepest parts of the ocean.

Halophilic

salt-loving organisms

Haloduric

do not prefer to live in salty environments but are capable of surviving there (Staphylococcus aureus)

Constitutive genes

Genes that expressed at all times are called

Inducible genes

Genes that are expressed only when the gene products are needed

Mutation

A change in the characteristics of a cell caused by a change in the DNA molecule (genetic alteration) that is transmissible to the offspring is called a mutation.

Beneficial mutation

An example would be a mutation that enables the organism to survive in an environment where organisms without that mutation would die. Perhaps the mutation enables the organism to be resistant to a particular antibiotic

Harmful mutation

result in the production of nonfunctional enzymes.

Lethal mutation

happens when an enzyme that catalyzes a metabolic reaction essential to the life of the cannot catalyze the reaction, the cell will die.

Silent mutation

they have no effect on the cell.

Mutagens

Physical or chemical agents that caused an increased mutation rate

Mutants

organism containing the mutation

Lysogenic Conversion

temperate phages (also known as lysogenic phages) inject their DNA into the bacterial cell, involves bacteriophage and the acquisition of new viral gene.

Transduction

Transduction means “to carry across.” Some bacterial genetic material may be carried across from one bacterial cell to another by a bacterial virus; involves bacteriophages.

Transformation

a bacterial cell becomes genetically transformed after the uptake of DNA fragments (“naked DNA”) from the environment.

Conjugation

genetic material usually in the form of a plasmid, is transferred through a hollow sex pilus from a donor cell to a recipient cell.