Marine Microbiology 2 (Jason)

Question 1

Describe the marine nitrogen cycle

Answer 1

• Nitrogen dissolves into seawater.
• Dissolved nitrogen is converted to organic nitrogen by microbes.
• Some organic nitrogen diffuses back into the air as nitrogen gas via denitrification.
• Organic nitrogen is passed to heterotrophs via the consumption of microbes.
• When microbes die, some organic nitrogen sinks to the ocean floor along with the dead organic matter.

Question 2

Name the microbe responsible for the majority of nitrogen fixation

Answer 2

Trichodesmium spp.

Question 3

What metal is required for nitrogen fixation and what is produced to overcome the limited amount of this metal in the marine environment

Answer 3

Iron

Siderophores

Question 4

Describe the marine phosphorous cycle

Answer 4

• Phosphorous does not have a gaseous phase. The main phosphorous reservoirs are ground deposits.
• Ground deposits erode and phosphate particles are carried to the sea by rivers, or as dust particles in the air. These particles dissolve in coastal waters and begin diffusing out to more remote ocean areas.
• Microbes adapt to the low phosphorous input by making a range phosphatases to break down organic phosphorous. Some can replace the phosphorous in lipids with sulfur. Also good at stockpiling phosphorous as polyphosphate granules for later use.

Question 5

Describe hydrothermal vents and the microbial community that grows around them

Answer 5

• Hydrothermal vents are openings in volcanic rock in the deep sea.
• Seawater flows into the volcanic rock and superheated seawater is pumped out under pressure created by the magma. The seawater brings many organic compounds with it.
• The bacteria in and around these vents harvest hydrogen sulfide for energy and electrons.
• The microbes can fix carbon dioxide or use methane dissolved in the water for carbon.
• This leads to the growth of microbial mats around the hydrothermal vent.
• Not all vent-dwellers prey on external bacteria, so have developed symbioses with them.
• Riftia spp. tube worms capture H2S and O2, and pass this and CO2 to trophosomes which contain cells called bacteriocytes where symbiotic bacteria are kept. The bacteria oxidise the H2S with the O2 for energy and electrons and also fix the CO2. Some of these nutrients are passed to the host however the bacteriocytes will eventually be digested by the host to harvest more nutrients.

Question 6

Describe cold seeps and the microbial communities that form here

Answer 6

• Underwater hydrocarbon deposits are rich in methane and H2S.
• Sometimes these deposits seep out of cracks in the crust and into the ocean.
• In the microbial communities that form here, hydrogen sulfide is the source of electrons and energy, and methane is the carbon source.
• Beggiatoa spp. are common in these mats.

Question 7

Describe marine sediments

Answer 7

• Much of the ocean floor is made up of various kinds of sediments.
• These sediments vary from abyssal clays to calcareous siliceous oozes.
• Marine sediments are estimated to contain 1/3 to 1/2 of all biomass on earth.
• Archaea are very common in marine sediments. Almost 90% of sediment lipids are Archaeal.