Thiobiotic life

Question 1

Name 3 environmental changes across the redox discontinuity zone (RDZ)

Answer 1

lowering of pH, change from oxidising to reducing potential, reduction in percolation

Question 2

Name a physiological different in nematodes below and above the RDZ

Answer 2

nematodes below are longer and thinner

Question 3

What are the 3 sources of hydrogen sulphide below the RDZ

Answer 3

microbially assisted breakdown of organic matter (e.g. cysteine), oxidation of sulphates in seawater, and from hydrothermal vents & cold seeps

Question 4

How does the presence of sulphur change across the RDZ?

Answer 4

HS- dominates above the RDZ and H2S dominates below as pH decreases

Question 5

What is the risk of organisms living in areas of H2S and how is this avoided?

Answer 5

H2S can diffuse across membranes and poison aerobic respiration - many marine meiofauna have developed an impermeable outer layer to protect against this

Question 6

How are S- ions stopped from forming H2S, S2 in thiobiotic meiofauna?

Answer 6

sulphur-binding proteins tightly bind to and carry them to internal detoxification centres, where its reducing power is used for metabolic gain

Question 7

Give the 2 risks of free sulphide ions

Answer 7

forming H2S, which binds to the cytochrome oxidase system in the electron transport chain, and oxidising into S2, which precipitates in blood vessels

Question 8

How do many thiobiotic macrofauna protect themselves against H2S?

Answer 8

by developing a complete reliance of anaerobic respiration, removing the need for a cytochrome oxidase system

Question 9

Give a key adaptation of the Aphelenchus avenae nematode to thiobiotic conditions

Answer 9

it has a cytochrome electron transport system thats insensitive to H2S and HCN.

Question 10

Give 3 risks of H2S

Answer 10

binds to the cytochrome oxidase system in respiration, binds to methaemoglobin/oxidise haemoglobin, and is a neurotoxin that effects vertebrate pulmonary function.

Question 11

Give 3 examples of thiobiotic macrofauna forming a symbiotic relationship with sulphur-oxidising bacteria

Answer 11

Alvinella pompeijana house bacteria in epicuticular pockets, bivalve molluscs have bacteriocytes between their gills (identified by rubisco test), vestimentiferan tube worms have trophosome organs which reduce the oxygen concentration surrounding sulphur-oxidising bacteria inside