Zonation

Question 1

What is donation

Answer 1

Elemental cycling can lead to zonation
microbial metabolic reactions in the environment change its chemistry
the availability of PEDs and TEAs affects which microbes live where
positioning of different types of bacteria is largely governed by the redox potential of the system

Question 2

What are some features/characteristics ono microbial mats

Answer 2

often in extreme environments e.g., hypersaline, thermophilic, where predation is lower
widely distributed
stabilise and can induce lithification of sediments
complex ecosystems that are largely self sufficient

Question 3

How do microbial mats form?

Answer 3

1. mats begin with solid particles in water - act as a surface for cell attachment
2. biofilms develop, usually a single species
3. left undisturbed, biofilms thicken and other species join
4. vertically stratified species dependent on different metabolic needs and abilities

Question 4

What is EPS and what role does it have?

Answer 4

EPS = extra cellular polymeric substance. is an organic carbon substrate
Biofilm = the EPS and the cells within it.
EPS helps hold the mat together. as mat grows, more EPS is produced. Enzymes in EPS help break down organic substrates.
Clustering in mats allows pooling of resources, genetic info, symbiosis
EPS buffers environmental change (pH, desiccation, Eh or contamination)

Question 5

What are the stages of development in microbial mats?

Answer 5

1. Cyanobacteria, diatoms and micro algae dominate in early stages. produce organic C and organic N. (CO2 and N2 fixation)
2. Fermentative and heterotrophic bacteria colonise. Aerobic respires denitrifies, SRB and methanogens
3. aerobic heterotrophs deplete O2, SRB produce H2S
4. Chemolithotrophs, S oxidisers, PSB use the H2S ( as e donor)

Question 6

Describe mature microbial mats

Answer 6

are self-sufficient
steep micro-scale gradients in light, pH, Eh, redox-active elements
may reach steady state
many cells are mobile - can move to areas of the right conditions - chemotaxis
changes in layers can reflect environmental changes

Question 7

Describe the changes in cyclicality of microbial mats

Answer 7

at night, O2 production stops. O2 is depleted. HS- can diffuse upwards, bringing gate S oxidisers with it.
Alkaline zone expands
GSB and PSB move upwards too (sulfate reducers)
pH increases and more alkaline environment - so CaCO3 can precipitate