lecture 2 - fermentation systems

What is catabolism?

Breaking down molecules and releasing energy

What are the three main catabolic pathways?

Aerobic respiration, anaerobic respiration, anaerobic fermentation

What is aerobic respiration?

Breakdown of glucose using oxygen

What is the final electron receptor in aerobic respiration?

Oxygen

How much energy is captured from glucose through aerobic respiration?

~40%

What is anaerobic respiration?

Catabolism without oxygen using an inorganic electron receptor

What is the final electron receptor in anaerobic respiration?

An inorganic molecule

Examples of anaerobic electron receptors?

Nitrate, sulfate, carbon dioxide

What is anaerobic fermentation?

Catabolism without oxygen using an organic electron receptor

What is the final electron receptor in fermentation?

An organic molecule

How much energy is captured from glucose through anaerobic metabolism?

~2%

Which pathway generates the most energy?

Aerobic respiration

Why is anaerobic metabolism useful?

Allows survival without oxygen

What are possible fermentation products?

VFAs, methane, lactate, ethanol

What are obligate aerobes?

Organisms that require oxygen

What do obligate aerobes use?

Aerobic respiration only

What are microaerophiles?

Organisms requiring low oxygen levels

What oxygen level do microaerophiles require?

~1–15% oxygen

What are obligate anaerobes?

Organisms very intolerant of oxygen

What do obligate anaerobes use?

Anaerobic respiration or fermentation

What are facultative anaerobes?

Organisms that survive with or without oxygen

What do facultative anaerobes use when oxygen is present?

Aerobic respiration

What do facultative anaerobes use without oxygen?

Anaerobic respiration or fermentation

Why is oxygen toxic to obligate anaerobes?

They cannot detoxify reactive oxygen compounds

What happens when superoxide and hydrogen peroxide build up?

They damage cell components and can cause death

What enzymes help detoxify oxygen compounds?

Enzymes that remove superoxide and hydrogen peroxide

What is fermentation?

Anaerobic, enzyme-catalyzed breakdown of energy-rich compounds by microbes

What does fermentation require?

Anaerobic conditions and microorganisms

What are the three fermentation systems?

Batch, fed batch, continuous

What is batch fermentation?

All nutrients are added at the beginning

What happens during batch fermentation?

Nothing is added or removed until collection

What happens to substrate during batch fermentation?

It decreases

What happens to microbial biomass during batch fermentation?

It increases

What happens to product during batch fermentation?

increases

Why does product production slow in batch fermentation?

Substrate decreases and end products inhibit microbes

Examples of batch fermentation?

Beer, wine, silage, yogurt

What is an example of batch ethanol fermentation?

Yeast ferment glucose into ethanol

What happens to sugar during ethanol fermentation?

Yeast use it up

What happens to yeast during ethanol fermentation?

Yeast grow and divide

What happens to ethanol during fermentation?

Ethanol increases

What is fed-batch fermentation?

Substrate is added gradually during fermentation

How is substrate added in fed-batch fermentation?

With a pump

What is the advantage of fed-batch fermentation?

Higher biomass and product yields

What limits fed-batch fermentation?

Toxic end-product accumulation

What is continuous fermentation?

Constant substrate input and outflow

What leaves a continuous fermenter?

Cells, media, and end products

Why can continuous fermentation continue for long periods?

Substrate enters while products and cells leave

What is dilution rate?

The rate of flow into and out of the fermenter.

Why is dilution rate important?

It controls microbial growth and washout

What happens if dilution rate is too fast?

Microbes wash out

Why do microbes wash out?

They cannot grow fast enough to replace cells leaving

What happens if dilution rate is too slow?

End products accumulate and microbes overgrow

What is the ideal dilution rate?

Microbes remain in steady state with good product production

How long can continuous fermentation operate?

Weeks, months, or sometimes years

What are examples of continuous fermentation products?

Ethanol, lactic acid, butanol, citric acid, beer

What factors moderate fermentation?

Substrate, temperature, gas, mixing, pH, end-product removal

What controls substrate availability in the rumen?

Feed quality, quantity, and frequency

How are rumen end products removed?

VFA absorption and digesta flow

What controls rumen mixing?

Rumen musculature and rumination

What is the rumen temperature?

~39–40°C (102–104°F)

What increases rumen pH?

Saliva and VFA removal

What decreases rumen pH?

VFA production

How are gases removed from the rumen?

Eructation

Which gases are eructated from the rumen?

CO₂ and CH₄

How is oxygen controlled in the rumen?

O₂ is scavenged

Why is the rumen considered a fed-batch system?

Feed is added over time

Why is the rumen considered a continuous system?

Digesta and end products continuously leave

Why is the rumen a mixture of fed-batch and continuous fermentation?

Feed enters periodically while digesta/products leave continuously