Microbial Nutrition and Growth Quiz

Microbial Nutrition and Growth

• Microbial 'growth' is an increase in the population of microbes, resulting from the reproduction of individual microbes.
• Results of microbial growth include discrete colonies (aggregations of cells from a single parent cell) and biofilms (collections of microbes living on a surface in a complex community).

Oxygen Requirements

• Oxygen in O₂ and H₂O is non-toxic.
• Highly reactive oxygen can damage proteins, enzymes, and lipids.
• Reactive oxygen will steal electrons from compounds.
• Oxidizing agents are forms of reactive oxygen.
• Some toxic forms of oxygen include singlet oxygen (O₂), superoxide radicals (O₂-), peroxide anion (O₂²⁻), and hydroxyl radical (OH).
• Many organisms can live in various oxygen concentrations.
• Obligate aerobes require oxygen.
• Obligate anaerobes cannot tolerate oxygen.
• Facultative anaerobes can grow with or without oxygen.
• Aerotolerant anaerobes do not use oxygen but can tolerate its presence.
• Microaerophiles require a low percentage of oxygen.

Other Chemical Requirements

• Microbes require carbon (used by autotrophs and heterotrophs).
• Nitrogen is needed for amino acids and nucleotide bases.
• Phosphorus is essential to nucleic acids.
• Sulfur is important for protein folding.
• Trace elements are needed in small amounts.
• Growth factors are necessary organic chemicals that cannot be synthesized by some organisms.

Temperature

• Temperature affects the three-dimensional structure of proteins and lipid-containing membranes of cells and organelles.
• If temperature is too low, membranes become rigid and fragile, if it is too high membranes become too fluid.
• Temperature affects microbial metabolic activity (minimum, maximum and optimum growth temperatures).
• Different microbes thrive in different temperatures.

pH

• Organisms are sensitive to changes in acidity.
• Neutrophiles thrive in a narrow range around a neutral pH (6.5-7.5).
• Acidophiles prefer acidic environments.
• Alkalinophiles prefer alkaline environments.

Water Requirements and Growth

• Microbes need water to dissolve enzymes and nutrients.
• Water is an important reactant in many metabolic reactions.
• Endospores and cysts cease most metabolic activity in dry conditions.
• Water affects microbes through osmotic and hydrostatic pressures.

Osmotic Pressure

• Osmotic pressure is the pressure exerted on a semipermeable membrane by a solution containing solutes that cannot cross the membrane freely.
• Hypotonic solutions have lower solute concentrations than the inside of the cell, while hypertonic solutions have greater solute concentration.
• Obligate halophiles require high salt concentrations, while facultative halophiles tolerate high salt concentrations.

Hydrostatic Pressure

• Water exerts pressure proportional to its depth.
• Barophiles thrive under extreme hydrostatic pressure.
• Membranes and enzymes in barophiles depend on pressure to maintain their three-dimensional, functional shape.

Microbial Associations

• Organisms live in association with different species and they can be antagonistic, synergistic, and symbiotic.

Biofilms

• Microorganisms (MOs) predominantly reside in nature as biofilms.
• Biofilms form on surfaces such as rocks, medical devices and form as a result of quorum sensing.
• Within biofilms, there are complex relationships among numerous MOs, making many MOs more harmful when part of a biofilm.
• Scientists are seeking ways to prevent biofilm formation.

Culturing Microorganisms

• An inoculum (sample) is introduced into a medium, and the resulting growth is called a culture.
• Collected samples include clinical specimens, stored specimens, and environmental specimens.
• Proper standard precautions are essential to avoid contamination and infection.

Obtaining Pure Cultures

• Pure cultures are made up of cells from a single progenitor (aka axenic).
• Progenitor is termed colony-forming unit (CFU).
• Aseptic techniques prevent contamination of sterile substances or objects.
• Streak plates and pour plates are techniques used to achieve pure cultures.

Culture Media

• Variety of liquid and solid media are used to culture microbes.
• Nutrient broth is a common liquid medium (e.g., beef extract and peptones).
• Agar is a common addition to make media solid (e.g., Petri plates and slant tubes).
• Six types of general culture media include defined (synthetic), complex, selective, differential, anaerobic, and transport.

Preserving Cultures

• Refrigeration can store cultures for short periods.
• Deep-freezing at -50°C to -95°C can store cultures for years.
• Lyophilization can store cultures for decades.

Growth of Microbial Populations

• Most microbes reproduce by binary fission (one cell divides into two).
• Binary fission involves four steps.
• Generation time is the time required for one bacterial cell to grow and divide, and for a population of cells to double in number.
• Bacteria can be differentiated by their growth phases (lag phase, log phase, stationary phase, death phase).

Continuous Culture in a Chemostat

• A chemostat is an open system used to maintain a microbial population in a specific growth phase.
• It requires continually adding fresh medium and removing old medium.

Estimating Microbial Numbers

• Estimating the number of microorganisms is helpful for assessing infection severity, evaluating food preservation, measuring water contamination and evaluating disinfectants and antibiotics.