Week 6 Marine Symbiosis: From Deep Sea Hydrothermal Vents To Surface Ocean Phytoplankton

Question 1

How much surface organic matter makes it to the sea floor?

Answer 1

1% so it is very barren

Question 2

What is a source of life in the deep?

Answer 2

Hydrothermal vents

Question 3

Where are hydrothermal vents found?

Answer 3

Typically found along mid-ocean ridges

Question 4

What process allows so much life in the deep sea?

Answer 4

Chemolithoautotrophy

Question 5

How does chemolithoautotrophy work at hydrothermal vents?

Answer 5

Reduced products from hydrothermal fluids after fluid-rock interactions - H2S, CH4 and H2 - may be oxidised by oxygen in normal deep-sea water for chemosynthesis

Question 6

What are two unusual morphologies in biavalves and what are they used for?

Answer 6

1. Extensible foot for burrowing between rocks

2. Large red gills for the symbionts

Question 7

What is unusual about tube worms, and what question does this present?

Answer 7

They have no mouth or gut, so how do they get their energy

Question 8

Why are tube worms trophosome tissue red?

Answer 8

Intracellular symbionts contained in bacterosytes that are required from the environment

Question 9

How are do tube worms and other vent organisms, obtain energy?

Answer 9

Fuelled by symbiosis with chemosynthetic microorganisms

Question 10

How do tube worms perform chemosynthesis?

Answer 10

1. Blood circulating with haemoglobin attract H2S + O2 so they don’t react as bacteria need the energy
2. Can do chemosynthesis and generate OM
3. OM fed to tube worm

Question 11

What is the relationship between CO2 fixation and H2S uptake?

Answer 11

High CO2 uptake = high H2S uptake

Question 12

How does this image effect the primary productivity?

Answer 12

Increased CO2 uptake and H2S means higher productivity

Question 13

What is the primary pathway for symbiont carbon fixation?

Answer 13

rTCA cycle

Question 14

How did scientists find out that the rTCA cycle as the primary pathway for symbiont carbon fixation?

Answer 14

Stable carbon isotope data, C12 and C13 look at the ratio of the two, each reaction gives a unique signature of C fixation

Question 15

What do the symbionts change in the rTCA cycle?

Answer 15

They modify the ATP citrate lyase

Question 16

What did a metagenome study reveal about the symbionts in the tube worm?

Answer 16

Likely a mixotroph between the Calvin-Benson Cycle and the rTCA cycle and there is all the genes necessary for heterotrophic metabolism because they can be free living

Question 17

In the symbionts of the tube worms, which is the dominant carbon fixation pathway?

Answer 17

RTCA cycle

Question 18

In the bivalve calyptogena magnifica, how do they acquire symbionts and what extra role do their symbionts have?

Answer 18

Vertical transmission (inheritance) and S-oxidising

Question 19

In the bivalve bathymodiolus thermophilus, how do they acquire symbionts and what extra role do their symbionts have?

Answer 19

1. Environmental acquisition

2. S and CH4 oxidant symbionts

Question 20

Where are symbionts in the mollusc and why, and what else does the mollusc still need?

Answer 20

1. Gills, which are a gas-exchange surface

2. Still need sulfide and CH4

Question 21

There can be dual symbiosis at hydrothermal vents, what are sulphide-oxidisers called, and what are methane oxidisers called?

Answer 21

1. Thiotrophs

2. Methanotrophs

Question 22

This image shows that hydrogenate genes overlap with thiotrophs, but not methanotrophs, what does this mean?

Answer 22

That S-oxidisers can also oxidise H2 for their chemolithoautotrophic growth

Question 23

What does this image show?

Answer 23

That those that oxidise S and H contribute to an increase in CO2 and support growth

Question 24

In mussels, when does symbiotic colonisation begin?

Answer 24

During metamorphosis

Question 25

How does symbiosis work for shrimps at vent sites?

Answer 25

They have epibionts or ecosymbionts which are not embedded in their tissues or cells

Question 26

How shrimps at vents obtain nutrition?

Answer 26

1. Harvesting ectosymbionts

2. Ingesting their exudate after moulting

Question 27

What are the two types of bacteria at vent sites for shrimps?

Answer 27

E and y-proteobacteria, which are likely s-oxidisers

Question 28

Out of the two types of filamentous bacteria, which one is endemic?

Answer 28

E

Question 29

Why do you need N fixation in the open ocean?

Answer 29

1. All life needs N

2. N2 is unusable to most organisms because the triple N bond is hard to break

Question 30

What are the three paradigms about N-limitation>

Answer 30

1. N2 fixation is highest and most important to pp in open ocean regions
2. N2 fixers aren’t competitive for other resources
3. N2 fixation occurs where dissolved inorganic N is low

Question 31

How do we know about UCYN-A ecology?

Answer 31

Because of culture independent methods

Question 32

UCYN-A’s genome lacks photo system 2, Calvin cycle and TCA cycle, how do they survive?

Answer 32

Fish and nano sims uncovered the ectosymbiotic relationship with haptphytes

Question 33

How do UCYN-A contribute to N2 fixation?

Answer 33

High distribution and high growth rate

Question 34

Why are nutrient fixation rates higher where nutrients concentrations are the highest?

Answer 34

Shifts from trichdesmium to UCYN-A. Trichodesmiun thrives in oligotrophic waters

Question 35

What are the new paradigms regarding N2 fixation?

Answer 35

1. N2 fixation is highest and important to pp in coastal regions
2. N2 fixers are competitive for other resources
3. N2 fixation occurs where dissolved inorganic nitrogen is high