MP QUIZ 3: Microbial Growth

God Bless

Microbial growth

An increase in the number of cells

Minimum growth temperature

The lowest temperature at which a species will grow

Optimum growth temperature

The temperature at which a species grows best

Maximum growth temperature

The highest temperature at which growth is possible

Psychrophiles

Cold-loving microbes that grow at 0°C with an optimum of about 15°C; sensitive to temperatures above 20°C

Psychrotrophs

Organisms that grow at 0°C but have optimum temperatures of 20-30°C; common cause of food spoilage in refrigerators

Mesophiles

Moderate-temperature-loving microbes with optimum growth temperature of 25-40°C; most common type of microbe; includes most pathogens

Thermophiles

Heat-loving microbes with optimum growth temperature of 50-60°C; cannot grow below about 45°C

Hyperthermophiles

Extreme thermophiles with optimum growth temperature of 80°C or higher; mostly Archaea found in hot springs and hydrothermal vents

Record high temperature for bacterial growth

About 121°C near deep-sea hydrothermal vents

Why hyperthermophiles grow above 100°C in ocean depths

The immense pressure in the ocean depths prevents water from boiling even at temperatures well above 100°C

pH range for most bacteria

pH 6.5 to 7.5 (near neutrality)

pH range for molds and yeasts

pH 5 to 6 (more acidic than bacteria)

Acidophiles

Bacteria that are remarkably tolerant of acidity; can survive at pH values as low as 1

To neutralize acids produced by bacteria during growth that would otherwise inhibit their own growth

Why are chemical buffers added to culture media?

Peptones, Amino Acids, Phosphate salts

Examples of buffers in culture media

Advantage of phosphate salts as buffers

They exhibit buffering effect in the pH growth range of most bacteria and provide phosphorus (an essential nutrient)

Osmotic pressure

The pressure exerted by solutes in solution; high osmotic pressure removes water from cells

Plasmolysis

Shrinkage of the cell's cytoplasm when water leaves the cell in a hypertonic environment

Food preservation by osmotic pressure

High salt or sugar concentrations draw water out of microbial cells preventing their growth (e.g. salted fish honey sweetened condensed milk)

Extreme halophiles (obligate halophiles)

Organisms that require high salt concentrations for growth (e.g. nearly 30% salt in Dead Sea organisms)

Facultative halophiles

Organisms that do not require high salt concentrations but can grow at salt concentrations up to 2%; some tolerate up to 15% salt

Hypotonic environment effect on microbes

Water enters the cell; weak cell walls may cause osmotic lysis

Carbon

chemical requirement that is a a structural organic molecules and energy source

Percentage of bacterial dry weight that is carbon

50%

Organic materials: proteins, carbohydrates and lipids

Chemoheterotrophs carbon source

Carbon dioxide (CO2)

Autotrophs carbon source

14%

Percentage of bacterial dry weight that is nitrogen

About 4%

Percentage of bacterial dry weight that is sulfur and phosphorus combined

To form the amino group of amino acids in proteins

Primary use of nitrogen in cells

Decomposing proteins ammonium ions (NH4+), nitrates (NO3-) or gaseous nitrogen (N2) through nitrogen fixation

Sources of nitrogen for bacteria

Nitrogen fixation

The process by which certain bacteria convert gaseous nitrogen (N2) from the atmosphere into a usable form

Photosynthetic cyanobacteria and symbiotic bacteria living in legume roots (clover soybeans alfalfa beans peas)

Examples of nitrogen-fixing bacteria

Synthesis of sulfur-containing amino acids, thiamine and biotin

Give Sulfur uses in cells

Sources of sulfur for bacteria

Sulfate ion (SO4^2-), hydrogen sulfide (H2S) and sulfur-containing amino acids + most bacteria decompose proteins

Phosphorus uses in cells

Synthesis of nucleic acids (DNA RNA) and ATP; also found in phospholipids of cell membranes

Source of phosphorus for bacteria

Phosphate ion (PO4^3-)

Potassium magnesium and calcium

Give the other important elements microbes require as cofactors

Trace elements

Mineral or inorganic elements required in very small amounts (iron, copper, molybdenum, zinc); usually function as enzyme cofactors

Obligate aerobes

Organisms that require oxygen to live; grow only where high concentrations of oxygen have diffused

Facultative anaerobes

Organisms that can use oxygen when present but can continue growth by fermentation or anaerobic respiration when oxygen is not available; grow best where most oxygen is present but occur throughout

Examples of facultative anaerobes

Escherichia coli (E. coli) and many yeasts

Obligate anaerobes

Organisms that are unable to use molecular oxygen for energy-yielding reactions and are harmed by it; grow only where there is no oxygen

Examples of obligate anaerobes

Clostridium species (cause tetanus and botulism)

Aerotolerant anaerobes

Organisms that cannot use oxygen for growth but tolerate it fairly well; grow evenly throughout medium; oxygen has no effect

Examples of aerotolerant anaerobes

Lactobacilli (used in production of pickles cheese and other fermented foods)

Microaerophiles

Aerobic organisms that require oxygen but only at concentrations lower than those in air; grow only where low oxygen concentrations have diffused (middle of tube)

Reason obligate anaerobes are killed by oxygen

They lack the enzymes (superoxide dismutase and catalase) to neutralize toxic forms of oxygen

Singlet oxygen (^1O2)

Normal molecular oxygen boosted into a higher-energy state; extremely reactive

Superoxide free radicals (O2-)

Toxic form of oxygen formed during normal respiration; steals electrons from neighboring molecules causing chain reactions

Superoxide dismutase (SOD)

Enzyme that neutralizes superoxide radicals by converting them into molecular oxygen and hydrogen peroxide: 2O2- + 2H+ → H2O2 + O2

Catalase

Enzyme that converts hydrogen peroxide into water and oxygen: 2H2O2 → 2H2O + O2

Peroxidase

Enzyme that breaks down hydrogen peroxide without producing oxygen: H2O2 + 2H+ → 2H2O

Hydroxyl radical (OH-)

The most reactive form of oxygen; formed in cellular cytoplasm by ionizing radiation

Hydrogen peroxide

Toxic form of oxygen produced by SOD reaction; neutralized by catalase or peroxidase —> good disinfectant but not antiseptic

Catalase and superoxide dismutase (SOD)

Which enzymes do aerobes have?

Catalase and superoxide dismutase (SOD)

Which enzymes do facultative anaerobes have?

Neither catalase nor superoxide dismutase (SOD); they lack both

Which enzymes do obligate anaerobes have?

Superoxide dismutase (SOD) but not catalase

Which enzymes do aerotolerant anaerobes have?

Add hydrogen peroxide to a colony; if bubbles of oxygen are released catalase is present

How to detect catalase

Organic growth factors

Essential organic compounds an organism cannot synthesize and must obtain from the environment

Vitamins (function as coenzymes), amino acids, purines (A,G) and pyrimidines (C,U,T)

Examples of organic growth factors

Biofilm

A community of microorganisms attached to a surface and enclosed in a matrix of polysaccharides DNA and proteins (slime)

T

T/F: Most microbes grow attached to surfaces (sessile) rather than free floating (planktonic)

F: Biofilms can be found all around the environment

T/F: Biofilms are not ubiquitous in nature in water

T

T/F: Biofilms can be formed on any conditioned surface

Confocal Microscopy

how were biofilms discovered

Biofilm matrix composition

Primarily polysaccharides but also contains DNA and proteins; often called slime or hydrogel

Quorum sensing

Cell-to-cell chemical communication that allows bacteria to coordinate activity and group together into communities

70%

Percentage of human bacterial infections involving biofilms (CDC estimate)

Nosocomial infections related to biofilms

Infections acquired in health care facilities often related to medical catheters and indwelling devices

Dental biofilm

Dental plaque (forms on teeth)

Lactoferrin role in biofilm prevention

Binds iron inhibiting surface motility essential for biofilm aggregation in pseudomonads

Culture medium

A nutrient material prepared for the growth of microorganisms in a laboratory

Inoculum

Microbes introduced into a culture medium to initiate growth

Culture

The microbes that grow and multiply in or on a culture medium

Agar

A complex polysaccharide derived from marine algae used as a solidifying agent in culture media

Properties of agar

Few microbes can degrade it; liquefies at about 100°C; solidifies at about 40°C; remains liquid at 50°C for pouring

Agar slants

Test tubes of agar allowed to solidify at an angle to provide a large surface area for growth

Agar deeps

Test tubes of agar that solidify in a vertical position

Petri dishes (plates)

Shallow dishes with a lid that nests over the bottom to prevent contamination; used to hold agar media

Chemically defined medium

A culture medium whose exact chemical composition is known

Complex medium

A culture medium made up of nutrients including extracts from yeasts meat or plants; exact chemical composition varies slightly from batch to batch

Fastidious organisms

Organisms that require many growth factors (e.g. Neisseria Lactobacillus)

Microbiological assay

A test that uses bacterial growth to determine the concentration of a particular vitamin in a substance

Nutrient broth

A liquid complex medium

Nutrient agar

A complex medium with agar added —> solid (agar itself is not a nutrient)

Reducing media

Media containing ingredients that chemically combine with dissolved oxygen to deplete it; used for culturing obligate anaerobes

Anaerobic jar

A sealed jar in which oxygen is chemically removed using chemical packets (sodium bicarbonate and sodium borohydride generate H2 and CO2) with a palladium catalyst

Anaerobic chamber

A closed chamber filled with inert gases (typically 85% N2 10% H2 5% CO2) with air locks; used for large volumes of anaerobic work

OxyPlate

A Petri plate that becomes an anaerobic chamber; contains the enzyme oxyrase which combines oxygen with hydrogen to form water

Capnophiles

Microbes that grow better at high CO2 concentrations

Candle jar

A sealed jar containing a lighted candle that consumes oxygen producing elevated CO2 and lowered oxygen conditions

Selective media

Media designed to suppress unwanted bacteria and encourage growth of desired microbes

Bismuth sulfite agar (isolates Salmonella typhi); Sabouraud's dextrose agar (isolates fungi at pH 5.6)

Examples of selective media

Differential media

Media that make it easier to distinguish colonies of desired organisms from other colonies on the same plate

Blood agar

A differential medium containing red blood cells; used to identify bacteria that destroy red blood cells (hemolysis)

Beta-hemolysis

A clear ring around colonies where bacteria have lysed surrounding blood cells; characteristic of Streptococcus pyogenes

Mannitol salt agar

Both selective (7.5% NaCl selects for Staphylococcus) and differential (mannitol fermentation changes pH indicator color)