Microbial Growth 1-3 (Jason)

Question 1

What nutrients are needed by microbes

Answer 1

• Carbon, hydrogen, oxygen, phosphorous, and sulphur are needed in large amounts (macronutrients).
• Potassium, calcium, magnesium, and iron ions are used in large quantities.
• Prototrophs can synthesise all of the complex nutrients which they need from inorganic nutrients.
• Auxotrophs cannot and must get one or more complex nutrients from the environment around them.

Question 2

How do microbes get their nutrients for growth

Answer 2

Microbial energy acquisition
Phototrophs - use light to produce ATP by photosynthesis.
Chemotrophs - use chemicals to produce ATP. These can be organic (e.g. glucose) or inorganic (e.g. sulphur) and are used in reaction pathways to generate ATP (e.g. via glycolysis).

Microbial electron acquisition
Lithotrophs - use reduced inorganic compounds e.g. nitrogen, iron, sulphur.
Organotrophs - use organic compounds e.g. glucose.

Microbial carbon acquisition
Autotrophs - use carbon dioxide as their principal carbon source. Most do this via photosynthesis.
Heterotrophs - use reduced, preformed organic molecules e.g. glucose or methane.

Question 3

How do microbes take in nutrients

Answer 3

Passive diffusion

• Movement of molecules from an area of high concentration to an area of low concentration.
• No energy required from the cell.
• Requires a large concentration gradient for significant rates of uptake.
• Inefficient and slow.
• Limited to a few small useful molecules e.g. water, oxygen, and CO2.

Facilitated diffusion

• High to low concentration gradient.
• Doesn’t require energy.
• Size of concentration gradient impacts rate of diffusion.
• Uses carrier molecules called permeases.
• Transports other molecules such as glycerol, sugars, and amino acids.
• Rate of facilitated diffusion plateaus when the carrier becomes saturated. Known as the Carrier Saturation Effect.

Primary active transport

• Uses energy to transport molecules either down or against a concentration gradient.
• Involves permeases so carrier saturation effect is observed.

Active transport using proton motive force

• Some cellular processes lead to a proton gradient forming across the cell membrane.
• This leads to pH and electrical differences across the cell membrane which combine to give the proton motive force.
• The proton gradient can be used to generate ATP and move molecules across the membrane.
• A symporter moves the molecule and proton across the membrane in the same direction.
• An antiporter moves the molecule and proton across the membrane in opposite directions.

Question 4

Describe how microbe affect the wider world

Answer 4

Carbon cycle

• 50% of carbon fixation is carried out by microbes (autotrophy)
• Methane from ruminants is produced by microbes in the ruminant digestive system.
• Pelagibacter ubique Sar11 feeds on dead organic matter dissolved in the ocean. This produces nutrients required by algae for growth which in turn fix CO2.

Nitrogen Cycle

• Nitrogen-fixing bacteria such as Rhizobium sp. convert atmospheric nitrogen to ammonia (bioavailable form).
• Soil bacteria and fungi decompose organic nitrogen in dead organisms which releases ammonium ions that can be converted to nitrogen compounds. This process is called ammonification.
• Nitrification first oxidises ammonia or ammonium ions to nitrite. Nitrite is then oxidised to nitrate, the most usable form for plants. This process is carried out by nitrifying bacteria such as Nitrobacter sp.
• During denitrification nitrate is reduced to nitrogen gas. This process is carried out by denitrifying bacteria e.g. Pseudomonas.
• Microbes are the only form of life that can fix nitrogen.

Microbes and climate change

• Algae produce an osmolyte called dimethylsulphoniopropionate (DMSP).
• When the algae die they release their stores of DMSP which bacteria break down to release dimethylsulphide (DMS) gas.
• DMS supplies 50% of global biogenic sulphur to the atmosphere, which is returned to soils via rain.
• DMS encourages cloud formation which act as thermal shields, blocking and reflecting solar radiation back into space and cooling the planet.

Question 5

Describe the different ways bacteria can be cultured in the lab

Answer 5

Defined (or synthetic) medium

• All components and their concentrations are known.
• Medium is tailored to the microbe.

Complex medium

• Contains some ingredients of unknown composition or concentration.
• Used if nutritional requirements are unknown, or for simplicity.

Selective media

• Tailored to favour the growth of some microorganisms and inhibit the growth of others.
• Allows you to grow a particular kind of microbe from a complex sample.
• MacConkey agar is a mixture of bile salts and dyes. Bile salts inhibit the growth of microbes not found in the gut. Crystal violet inhibits the growth of Gram positive bacteria because it accumulates in their thick cell wall. Therefore MacConkey agar is selective for Gram negative enteric bacteria e.g. used for detection of E. coli in water.

Differential media

• Allows you to distinguish visually between different groups of microbes based on their biological characteristics.
• Blood agar distinguishes between haemolytic and non-haemolytic bacteria.
• MacConkey agar is differential for lactose fermenters. It contains the pH indicator Neutral Red and lactose. Lactose fermenters release lactic acid and turn agar red.

Question 6

How are microbes exploited industrially

Answer 6

• Industrial processes - bioleaching, production of alcohol, amino acids, and pharmaceuticals.
• Anaerobic microorganisms are used to treat organic waste in wastewater treatment. Methanogenic microbes then produce biogas with up to 80% methane content that is used to supply green energy.
• Yeast is used to ferment the sugar in plants, converting it to ethanol which is the most common primary biofuel.
• Biodegradation can be defined as the breaking down of organic matter to gain nutrients and energy for growth and survival. Environmental microbiologists can manipulate these processes to clean up sites contaminated with toxic chemicals (bioremediation).
• Sometimes microbes which are capable of breaking down a pollutant do not exist in that environment. Many companies produce microbial mixtures for specific purposes which can be added. This is known as bioaugmentation.