Lecture 35

Question 1

What is desulfuration? What is the equation?

Answer 1

The decomposition of organic matter to recycle organosulfur compounds.
R-SH -> H2S

Question 2

What is sulfur respiration (anaerobic)? What is the equation?

Answer 2

The reduction of S0 as a TEA via anaerobic respiration to yield H2S.
S0 -> H2S

Question 3

What is the equation for dissimilatory sulfate reduction?

Answer 3

SO4- -> H2S

Question 4

What are the 3 ways in which H2S is produced in the sulfur cycle?

Answer 4

Desulfuration, dissimilatory sulfate reduction (anaerobic respiration), sulfur respiration (anaerobic)

Question 5

What is the main function of aerobic oxidation of sulfide and sulfur?

Answer 5

The oxidation of sulfide and sulfur to sulfate (with O2 as TEA) is important for energy generation. It is also a source of electrons for biosynthesis.

Question 6

What is the formula for sulfide oxidation (aerobic)?

Answer 6

H2S -> S0

Question 7

What is the formula for sulfur oxidation (aerobic)?

Answer 7

S0 -> SO42-

Question 8

Give 2 examples of organisms that do sulfide oxidation?

Answer 8

Beggiatoa, Thiothrix (sulfur bacteria) - they oxidize H2S and accumulate S0 intracellularly.

Question 9

Give an example of an organism that oxidizes S0 to sulfuric acid.

Answer 9

Sulfolobus (archaea)

Question 10

What is the energy yield of the aerobic sulfur-oxidizing reactions?

Answer 10

Sulfide oxidation: 50 kcal/mol
Sulfur oxidation: 150 kcal/mol
Very energetically favourable reactions.

Question 11

Name the two forms of anaerobic oxidation of sulfur and sulfide.

Answer 11

Chemotrophic anaerobic oxidation and phototrophic anaerobic oxidation.

Question 12

What is chemotrophic anaerobic oxidation of sulfide and sulfur? What is the formula?

Answer 12

It is the oxidation of sulfides or sulfur with TEAs other than O2. Yields S0 or SO42-.
H2S -> S0 -> SO42-

Question 13

Give two examples of chemotrophic anaerobic oxidation of sulfide and sulfur.

Answer 13

Thiomargarita and Beggiatoa use H2S as an energy source AND electron source with NO3- as TEA.

Question 14

What is phototrophic anaerobic oxidation of sulfide and sulfur? What is the formula?

Answer 14

It is the use of sulfides or S0 as an ELECTRON SOURCE. Yields S0 or SO42-.
H2S -> S0 -> SO42-

Question 15

Give an example of a sulfur gradient organism and explain its lifestyle.

Answer 15

Beggiatoa grow at the interface of O2 and H2S gradients to oxidize H2S, forming S0 and/or sulfate.

They are capable of both aerobic or anaerobic chemotrophic sulfide oxidation. In the aerobic case, the TEA is O2. In the anaerobic case, the TEA is internally stored NO3- when O2 is unavailable.

Question 16

Consider a lake with an anerobic and aerobic zone, and with desulfovibrio, thiobacillus, and chlorobium. Describe what happens given an input of SO42- for each bacteria, including the name of the reaction.

Answer 16

Desulfovibrio at the bottom of the lake will do dissimilatory sulfate reduction of SO42- to H2S.

In the anaerobic zone: Chlorobium will then use the H2S to do anaerobic phototrophic sulfide oxidation. This will yield S0 that gets deposited at the bottom of the lake.

In the aerobic zone: Thiobacillus will take the H2S and do aerobic chemotrophic sulfide oxidation to S0, which will also sink to the bottom of the lake.

Question 17

Consider a hydrocarbon deposit with an anaerobic and aerobic zone that receives an influx of SO42- in the anaerobic zone. Describe what will happen to it and the relevant bacteria and reactions (name them).

Answer 17

Organisms such as desulfovibrio will use the SO42- for anaerobic respiration to produce H2S. The H2S will rise into the aerobic zone. It will be used by other organisms that will do aerobic sulfide oxidation to S0.

Question 18

What is the equation for assimilatory sulfate reduction?

Answer 18

SO42- -> R-SH

Question 19

What is the purpose of assimilatory sulfate reduction? How does it work?

Answer 19

Allows for the formation of amino acids (Cys, Met), etc. It is tightly regulated because cells only need a relatively small amount of S. This pathway is subject to end-product inhibition.

Question 20

How regulated is dissimilatory sulfate reduction?

Answer 20

It is not tightly regulated and is not subject to end-product inhibition.

Question 21

Describe how dissimilatory sulfate reduction works and what organisms do it.

Answer 21

Use SO42- as the TEA in anaerobic respiratory, and H2 and/or organic carbon as energy and electron source. This is done by sulfate-reducing bacteria.

Question 22

Where are SRBs found in the sediment column?

Answer 22

They are located in the SO42- layer above the methanogens.

Question 23

What was the purpose of the Risatti paper?

Answer 23

To study a complete community of SRBs in a microbial mat and determine whether they had different functions and how this related to their spatial organization.

Question 24

Describe the methods used by Risatti et al.

Answer 24

They took a core sample and isolated RNA that they slot blotted to membranes. The membranes were then hybridized with radioactive 32P probes. This allowed for the quantification of different species. The plots were then stripped of the probe and rehybridized with each of the other probes. Densitometry was performed and then relative densities of SRB groups vs sample depth were plotted.

Question 25

What types of probes were used by Risatti et al.?

Answer 25

They used 5 different SRB probes for 16S rRNA, one for each SRB genus or family of closely-related genera. This was to quantify different SRB groups. They also used a universal probe to detect all organisms and calculate relative proportion sizes. Lastly, they used an archaeal probe to detect archaea such as methogens and extreme halophiles.

Question 26

Describe the findings of Risatti et al. in terms of absolute population sizes.

Answer 26

They found that there is overall more 16S at shallow depths than at deeper depths. They also found that different groups had their own specific depths that they dominated - they are stratified.

Question 27

Describe the major conclusions of the Risatti paper.

Answer 27

This was the first time that the spatial distribution of microorganisms in a microhabitat had ever been demonstrated. The distribution of SRB groups is likely significant and was also observed in later studies.

This indicated that the phylogenetic groups have different metabolic capabilities that can influence their distribution in the habitat. Each group appears to have their own niche in the food web.

Question 28

What is the relative positioning of SRBs and cyanobacteria?

Answer 28

SRBS tend to be located under the cyanobacteria. There can be a lot of SRBS relatively close to the surface.

Question 29

What types of reactions tend to happen along the gradient of O2 and H2S?

Answer 29

There is often sulfide production.