Microbiology Chapter 6

Essential nutrient

Any substance that must be provided to an organism. The organism needs to take in that substance to survive.

Macronutrients

Required in relatively large quantities and play principal roles in cell structure and metabolism. EX. Carbon, hydrogen, and oxygen

Micronutrients (trace elements)

Present in much smaller amounts and are involved in enzyme function and maintenance of protein structure. EX. Magnesium, zinc, and nickel.

Heterotroph

An organism that must obtain its carbon in an organic form.

Autotroph

An organism that uses inorganic CO2 as its carbon source. They can convert CO2 into organic compounds. Not nutritionally dependent on other living things (self-feeder).

Photoautotroph

Energy source: Sunlight

Carbon source: Carbon dioxide

Example organisms: Algae, plants, and cyanobacteria

Photoheterotroph

Energy source: Sunlight

Carbon source: Organic

Example organism: Purple and green photosynthetic bacteria

Chemoautotroph

Energy source: Organic compounds

Carbon source: Carbon dioxide

Example organism: Methanogens

Chemoheterotroph

Energy source: Metabolic conversion of the nutrients from other organisms

Carbon source: Organic

Example organisms: Protozoa, fungi, many bacteria, and animals

Phototroph

A microbe that photosynthesizes, meaning it uses the sun for energy.

Chemotroph

A microbe that gets its energy from chemical compounds.

Chemolithotrophs

Receive their energy from inorganic compounds or minerals because they can convert carbon dioxide.

Saprobes

Metabolize the organic matter from dead organisms; they are heterotrophs, so they take in carbon as an organic compound.

Parasites

Derive nutrients from the cells or tissues of a living host. Take in carbon as an organic compound. Range from viruses to helminths. Types: Ectoparasites, endoparasites, intracellular parasites, and obligate parasites

Ectoparasites

Organisms that live on the body.

Endoparasites

Organisms that live in the organs and tissues of the host.

Intracellular parasites

Organisms that live within cells of the host.

Obligate parasites

An organism that is unable to grow outside of a living host. They can only reproduce within the cells of a host. 

Pathogens

Cause damage to tissues or even death.

Carbon

Acts as the structural backbone for organic molecules and is used as an energy source. Organisms use it to make all macromolecules. Heterotrophs obtain it from organic carbon sources. Autotrophs take in carbon dioxide as their carbon source. 

Carbon

How element is obtained: Heterotrophs through organic compounds and autotrophs through carbon dioxide.

Used to make: All macromolecules

Hydrogen

Acquired through organic compounds and several inorganic compounds, including water (H2O), salts (Ca[OH]2), and certain naturally occurring gases (H2S, CH4, and H2). Helps cells maintain their pH, is useful for forming hydrogen bonds between molecules, and also serves as a source of free energy in respiration.

Hydrogen

How element is obtained: Organic compounds and inorganic compounds (water, salts, and certain naturally occurring gases

Used to make: All macromolecules

Nitrogen

Used to make proteins and nucleic acids (ATP). Most bacteria decompose proteins to get a source of nitrogen. Some bacteria use NH4+ (ammonium already in reduced form) or NO3– (nitrate) from organic material. A few bacteria use N2 gas from the atmosphere in nitrogen fixation

Nitrogen

How element is obtained: Decomposing proteins, ammonium or nitrate from organic material, or nitrogen gas from the atmosphere.

Used to make: Proteins and nucleic acids (ATP)

Atmospheric nitrogen

Makes up about 70% of the gas in our atmosphere. Most organisms cannot take in nitrogen from this form. If they are able to do this, it is referred to as nitrogen fixation.

Sulfur

Used by organisms to make amino acids and vitamins. Most bacteria decompose proteins for their sulfur source. Some bacteria use SO42– (sulfate ion) or H2S (hydrogen sulfide) to take in sulfur.

Sulfur

How element is obtained: Decomposing protein or using sulfide ion or hydrogen sulfide.

Used to make: Amino acids and vitamins (organic compounds used to help enzymes function)

Phosphorus

Used to make nucleic acids (DNA, RNA, ATP) and cell membranes. Organisms use PO43– (phosphate ion), which is a source of phosphorus. The phosphate ion is found in rocks and oceanic mineral deposits.

Phosphorus

How element is obtained: Phosphate ion, which is found in rocks and oceanic mineral deposits

Used to make: Nucleic acids (DNA, RNA, ATP) and cell membranes

Trace elements

Inorganic elements(lack carbon and hydrogen) required in small amounts. Usually act as enzyme cofactors. EX. Iron, copper, and zinc

Oxygen

Used to make all the macromolecules. It is obtained through organic compounds and inorganic salts such as sulfates, phosphates, nitrates, and water. It plays an important role in the structural and enzymatic functions of the cell.

Oxygen

How element is obtained: Organic compounds and inorganic salts (sulfates, nitrates, phosphates, and water)

Used to make: All macromolecules

Atmospheric gases that affect microbial growth the most

Oxygen and carbon dioxide

Oxygen

Has the greatest impact on microbial growth. It is a respiratory gas that acts as the final electron receptor in aerobic cellular respiration. Also, an oxidizing agent.

Toxic products of oxygen entering cellular reactions

1. Singlet oxygen (O): An extremely reactive molecule that can damage and destroy a cell by the oxidation of membrane lipids. Not stable in the cell. 

2. Superoxide ion (O2–): Highly reactive. 

3. Hydrogen peroxide (H2O2): Toxic to cells and used as a disinfectant. 

4. Hydroxyl radical (OH–): Also highly reactive

Singlet oxygen (O)

An extremely reactive molecule that can damage and destroy a cell by the oxidation of membrane lipids. Not stable in the cell. 

Superoxide ion (O2–)

Highly reactive. 

Hydrogen peroxide (H2O2)

Toxic to cells and used as a disinfectant. 

Hydroxyl radical (OH–)

Also highly reactive

Enzymes that neutralize reactive oxygen products

1. Superoxide dismutase (SOD) is used to neutralize superoxide ions. They will convert those ions into hydrogen peroxide(also unstable) and oxygen gas. 

2. Catalase is used to neutralize the unstable hydrogen peroxide and convert it into water and oxygen gas. Used by organisms that use oxygen as the final electron receptor.  

3. Peroxidase is used by organisms that do not utilize calalase. Neutralizes hydrogen peroxide and produces water only. Used by organisms that grow in oxygen but don’t use it.

Superoxide dismutase (SOD)

Used to neutralize superoxide ions. They will convert those ions into hydrogen peroxide(also unstable) and oxygen gas. Used by organisms that grow in the presence of oxygen. (aerobic respiration)

Catalase

Used to neutralize the unstable hydrogen peroxide and convert it into water and oxygen gas. Used by organisms that use oxygen as the final electron receptor. (aerobic respiration)

Peroxidase

Used by organisms that do not utilize calalase. Neutralizes hydrogen peroxide and produces water only. Used by organisms that grow in oxygen but don’t use it.

Aerobes

Organisms that use molecular oxygen as the final electron acceptor in aerobic respiration.  

Anaerobes

Organisms that do not require oxygen, or it is toxic to them. 

Obligate Aerobe

Requires oxygen. EX. Pseudomonas aeruginosa - causes infections in burn victims and patients with CF

Microaerophile

Requires low O₂ concentrations. EX. Helicobacter pylori - causes ulcers 

Obligate Anaerobe

Ceases growth or dies in the presence of O₂. EX. Clostridium perfringens - causes gangrene, produces an endospore to protect itself when in O₂

Facultative Anaerobe

Grows with or without O₂, but will grow better with it. EX. Escherichia coli - causes UTIs

Aerotolerant Anaerobe

Tolarates O₂. Can grow in O₂, but they do not use it. EX. Streptococcus pyogenes - causes strep throat

Thioglycollate broth

Uses a reducing media to create an anaerobic environment. The broth contains L-cysteine and sodium thioglycollate, which reduces oxygen to water. This made the bottom of the tube anaerobic. Resazurin was used as an oxygen indicator. 

Capnophiles

Organisms that grow best at a higher CO2 tension than is normally present in the atmosphere. These organisms would require a lower oxygen concentration and a higher carbon dioxide concentration. These organisms can be grown in a candle jar. EX. Neisseria, Brucella, and Streptococcus pneumoniae. 

Minimum growth temperature

The lowest temperature that permits a microbe's continued growth and metabolism. Below this temperature, activity stops. 

Optimum growth temperature

An intermediate between the minimum and the maximum that promotes the fastest rate of growth and metabolism. 

Maximum growth temperature

The highest temperature at which growth and metabolism can proceed before proteins are denatured. If the temperature goes above this, growth will be inhibited and in many cases, kill the bacteria.

Psychrophile

Name means cold lover. They grow between 0-20 °C and optimally below 15°C. Storage at refrigerator temperature causes them to grow rather than inhibiting them. Natural habitats include lakes, rivers, snowfields, polar ice, and the deep ocean. Rarely pathogenic because they do not grow at human body temperature.

Psychrotrophs

Name means cold eater. Grow between 0-30°C and optimally between 15-30°C. Most don’t cause disease because they don’t grow well at 37°C (Human body temperature). Usually causes food spoilage. EX. Listeria monocytogenes causes listeriosis. People most at risk of this are immunocompromised and fetuses.

Mesophile

Name means moderate lover. They grow between 10-50°C and optimally between 20-45°C. They are the most common spoilage and disease-causing organisms because they grow well at 37°C (human body temperature). EX. E. coli- sepsis, UTI, food poisoning, and S. aureus- skin infections, sepsis, pneumonia (kills more people than AIDS)

Thermoduric

An organism that is normally a mesophile, but can survive short exposure to high temperatures. These organisms are common contaminants of heated and pasteurized foods. EX. Bacillus and Clostridium because they produce endospores.

Thermophile

Name means heat lover. They grow between 45-80°C and optimally between 50-60°C. They live in sunlit soil and water associated with volcanic activity, compost piles, and hot springs. Most eukaryotic forms can not survive above 60°C.

Do most psychrotrophs cause human disease?

No, most cause food spoilage, not human disease.

Which temperature requirements organisms cause the most food spoilage and human disease? Why?

Temperatures between 10℃-50℃ cause most bacteria to grow rapidly. Organisms known as mesophiles grow best at these temperatures and can cause food spoilage and human disease.

Why can a fever be useful for the body?

A fever is useful because it increases body temperature, which can make mesophiles slow down the growth.

pH of bacteria

Most bacteria grow between a pH of 6.5-7.5. Molds and yeast grow best between 5-6.

Acidophile

Grows best in an acidic environment. This is the case for most food spoilage microbes. EX. Lactobacillus 

Neutrophile

Grows best in neutral pH environments (around 7). This is the case for most normal microbiota (flora). EX. E. coli

Alkaliphile

Grows best in an alkaline environment. EX. Proteus

Which pH requirement organisms are likely to be the case for most food microbes (that cause spoilage)?

Most microbes that cause food spoilage are acidophiles. 

Which pH requirement organisms are likely to be the case for most normal microbiota (flora)?

Most normal microbiota (flora) are neutrophils.

What happens to most bacteria when placed in hypertonic environments (in a solution with high concentration of salt or sugar)?

It causes plasmolysis, which causes the cell membrane to collapse in; this inhibits microbial growth. 

Symbiotic relationship

When organisms live in a close nutritional relationship. This interaction is required by either one or both organisms. Types: Mutualism, commensalism, and parasitism. 

Obligate halophile

Organisms that require high osmotic pressure

Facultative halophile

Organisms that tolerate high osmotic pressure

Nonsymbiotic relationship

When organisms are free-living, meaning they do not require a relationship for their survival. 

Synergism

A form of a nonsymbiotic relationship where members cooperate and share nutrients. EX. Biofilm, a mixed community of bacteria that is attached to a surface and each other.

Antagonism

A form of a nonsymbiotic relationship where members are inhibited or destroyed by others. 

Chemically defined media

Exact chemical composition is known. Used to culture fastidious organisms, which are organisms that have specific nutritional needs. 

Complex (undefined) media

Contains extracts and digests of yeast, meat, or plants. The exact chemical composition of the media varies from batch to batch. EX. Nutrient broth

Reducing media

Used for the cultivation of anaerobic bacteria. It contains chemicals that reduce oxygen to water, making it anaerobic. EX. Anaerobic jar

Selective media

Suppresses unwanted microbes and encourages growth of desired microbes. Contain inhibitors to suppress growth

Differential media

Allows us to distinguish colonies of different microbes on the same plate.

Biofilms

Form when a “pioneer” bacterium attaches and colonizes an initial surface. The pioneers will secrete a polymeric sugar or protein to attract other microbes. Or other microbes will just attach to those pioneer bacteria. These attached cells are stimulated to release chemicals as the cell population grows. 

Biosafety level 1

Not known to consistently cause disease in healthy adults. No special precautions needed. EX. E coli

Biosafety level 2

Moderate hazard to personnel and the environment. Lab coat, gloves, and eye protection are needed when handling these organisms. EX. Hepatitis A

Biosafety Level 3

Microbes that are either indigenous or exotic and they can cause serious or potentially lethal disease. These bacteria are kept in biosafety cabinets to prevent airborne transmission. EX. West Nile Virus 

Biosafety Level 4

Dangerous and exotic microorganisms that pose a high risk of aerosol-transmitted infections. Infections caused by these microbes are often fatal. They need to be sealed under negative pressure. EX. Ebola virus

Types of Reproduction in Prokaryotes

1. Binary fission 

2. Budding

3. Conidiospores (actinomycetes)

4. Fragmentation of filaments

Binary fission (genetically identical)

A cell enlarges, duplicates its chromosomes, the cell envelope forms in the center of the cell, and finally, the cell divides into two genetically identical cells. 

Budding

A small outgrowth comes off the main cell. It will eventually bud off and gradually increase in size. 

Conidiospores (actinomycetes)

A fungal-like bacterium that reproduces using conidiospores

Generation time

The time required for a cell to divide and its population to double. Most bacteria can double in 30-60 minutes. The number of cells in each generation is 2n. Where n is the number of doublings (generations) that have occurred.

Phases of Growth

1. Lag phase

2. Log phase

3. Stationary phase

4. Death phase

During which phase of the growth curve are endospores most likely to be produced?

Endospores form during the stationary phase due to harsh conditions

Lag phase

Appears flat because newly inoculated cells require an adjustment period (High metabolic activity). Will not see much growth due to the cells getting ready to divide

Log phase

Growth of microbes increases at a constant rate. This will continue as long as cells have adequate nutrients and the environment is favorable. 

Birth rate ﹥ Death rate 

Stationary phase

Cell division is slowing down, with no change in population size. Caused by depleted nutrients and a buildup of waste products. (endospores form here due to harsh conditions)

Birth rate=death rate.

Death phase

Cells begin to die at an exponential constant rate due to waste products and a lack of nutrients. The speed at which death occurs depends on the resistance of the species. Some cells may remain viable.

Birth rate ﹤ Death rate.

Turbidity/turbidometry

A clear nutrient solution becomes turbid, or cloudy, as microbes grow in it. The greater the turbidity, the larger the population size

Direct cell count

Measured microscopically