Microbiology Ch 6: Microbial Nutrition & Growth

What is a psychrophile?

thrives in cold temperatures (-10C—20C)

What is a mesophile?

thrives in moderate temperatures (10C—50C)

What is a thermophile?

thrives in high temperatures (40C—70C)

How can you interpret a graph to understand the optimal temperature of an organism?

the peak indicates the optimal temperature for the organism's growth

What is an acidophile?

organisms that grow best at pH < 5.5

What is a neutrophile?

organisms that grow best at pH 5.5-8.5

What is an alkaliphile?

organisms that grow best at pH > 8.5

How are phototrophs characterized?

uses light as primary source of energy

How are chemotrophs characterized?

depend on oxidation-reduction (redox) reactions of organic and inorganic compounds for energy

How are heterotrophs characterized?

must obtain carbon in its organic form and is dependent on other life forms

How are autotrophs categorized?

uses inorganic CO₂ as carbon source and is not dependent on other life forms

What are photoautotrophs?

photosynthetic organisms that convert light energy (CO2) into chemical energy (organic molecules)

What are chemoautotrophs?

organisms that use CO2 as principle source of C, exists on inorganic minerals, and does not require sunlight

How do chemoautotrophs obtain energy?

removes electrons from inorganic compounds and combines it with CO2 and H2

Where can chemoautotrophs be found?

deep ocean or underground (in the soil)

Most heterotrophic living things are classified as...

chemoheterotrophs

What characterizes chemoheterotrophs?

chemoheterotrophs get carbon and energy (ATP) from organic compounds

How do chemoheterotrophs obtain energy?

through cellular respiration or fermentation (if no O2 present)

How is nitrogen obtained?

decomposing proteins (NH4+) and N2 in the air

Why is nitrogen essential to life?

Used to make up proteins (amino group) and nucleic acids (nitrogenous base)

What is nitrogen fixation?

obtaining nitrogen from N2 in the atmosphere

How can oxygen be toxic to some organisms?

cellular respiration produces toxic by-products that need to be neutralized

2O₂^- + 2H⁺ → ____ + __

H₂O₂ + O₂

What enzyme is needed for 2O2- + 2H+ → H2O2 + O2?

superoxide dismutase (SOD)

2H2O2 → ____ + __

2H₂O + O₂

What enzyme is needed for 2H2O2 → 2H2O + O2?

catalase

What is the definition of an aerobe?

able to metabolize oxygen and has the enzymes to process toxic oxygen products

What is an obligate aerobe?

organism that requires oxygen for growth

What is a facultative anaerobe?

an organism that doesn't require oxygen for metabolism, but will grow better in the presence of oxygen

What is a microaerophile?

an organism that only requires a small amount of oxygen to grow

What is the definition of an anaerobe?

lacks enzymes to utilize oxygen

What is an obligate anaerobe?

organism that cannot process toxic oxygen and will die in presence of oxygen

Where can you find obligate anaerobes?

deep mud, lakes, oceans, soil

Why do we use sodium thioglycolate in media when determining oxygen requirements of microorganisms?

sodium thioglycolate is a reducing agent that removes oxygen from media

How do we culture obligate anaerobes?

we use an anaerobic jar that has a gas pack (ie Gaspak), which produces H2O from the combination of H2 and oxygen in the chamber

How can we tell if oxygen is present in the anaerobic jar?

chemical indicator strip (usually methylene blue, which becomes colorless in absence of O2)

What are biofilms?

coordinated, functional communities that reside in a matrix of polysaccharides, DNA, and proteins

How do biofilms work?

bacteria share nutrients among each other and are protected from desiccation, antibiotics, and immune cells

What are two indicators of microbial growth?

increase in cell size, increase in cell number

What is binary fission?

asexual reproduction used by bacterial cells that produces 2 daughter cells from 1 parent cell

Why is bacterial growth exponential?

because 1 cell produces 2 daughter cells

What is the formula for bacterial growth?

x2ⁿ, where x = initial amount of cells and n = generation number

What is generation time?

time required for complete fission cycle (doubling of population)

What is the typical generation time for bacteria?

0.5 - 3 hrs

Why is the population growth curve not realistic over a long period of time?

Lack of nutrients

Limited space

Accumulation of waste changing pH level

Define the lag phase of a growth curve.

little or no cell division occurring, the cells are undergoing intense activity preparing for population growth

Define the log phase of a growth curve.

exponential growth, cells are most metabolically active and also most vulnerable

Define the stationary phase of a growth curve.

multiplication rate = death rate, nutrients and oxygen are depleted while toxins accumulate, causing change in pH

Define the death phase of a growth curve.

cell deaths > new cells

What device do we use to estimate bacterial numbers?

spectrophotometer

What does the spectrophotometer measure?

turbidity, which gives us the optical density (OD) that determines absorbance

Binary fission process

1) Parent cell elongates, DNA replicated

2) Cross-wall forms separating each DNA

3) Cells divide into 2 identical daughter cells

Equation for binary fission

2ⁿ

Where n = number of divisions/generations