Complete lecture notes of BIO231 Microbial Physiology and Growth week 9 on Anaerobic Respiration Denitrification and Sulfate Reduction. Includes all the lectures slides content along with word-for-word commentary from lecturer and in red is my personal commentary that explains some concepts in easi...
Week 9 - Anaerobic Respiration;
Denitrification and Sulfate Reduction
Saturday, 25 March 2023 09:44
LO1: understand the difference between aerobic and anaerobic respiration
LO2: describe the basic pathways and energetics involved in nitrate reduction and
denitrification
LO3: describe the basic pathways and energetics involved in sulfate reduction
Anaerobic Respiration
The rise of oxygen over time
- Atmospheric oxygen wasn't always available on earth although life was ALREADY
present (4 billion years ago)
- Earliest microfossils occurred 3.5 billion years ago
- These events all happened during the Archean period where there was a lack of oxygen,
so the microbes used anaerobic respiration or fermentation
Present Day - Anoxic environments
The Black Sea
- Presently, we STILL have anoxic
environments, the biggest
natural one being the black sea
- The Mediterranean sea (high
salinity) and Danube river
(freshwater) both flow to the
black sea, the different salinity
levels have different densities
- The sea water flows towards
,
, - The Mediterranean sea (high
salinity) and Danube river
(freshwater) both flow to the
black sea, the different salinity
levels have different densities
- The sea water flows towards
bottom of black sea (bc of higher
density compared to fresh
water), and the fresh water
Figures from Banaducet al (2016) Science of the Total Environment 545–546: (with its oxygen) stays on top,
137.and Save the Sea™. Dead Zone. For more information please visit
https://savethesea.org/STS%20dead%20zones.htm not mixing
- At 150m is where the anoxic sea
water is, while top is freshwater
- At around 150m is where there is 0% oxygen and significant increase in sulfide the
deeper you go (because of sulfate reduction microbes) but there still are microbes living
in this environment
On a smaller scale…
- Say we're looking at a water column depth of 2 mm, notice how quickly the [oxygen]
rises and at -2 mm it quickly drops, turning into an anoxic environment in the sediment
- Meaning great depths aren't needed in a sediment for the anoxic environment to occur
- In this sediment column are different levels of metabolism available for the different
microbes; obligate aerobe (will be 2mm area), facultative anaerobe (2-0mm area
because it prefers oxygen even if it can do without it), obligate anaerobic (-2mm and
below)
- In the sediment, there is a drop in oxygen because it’s a solid surface, the deeper you go
,o
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