what are the 5 alternative electron acceptors
- nitrate (NO3-), nitirite (NO2-), sulfate (SO42-), Carbon dioxide (Co2), proton (H+)
- avaiable energy sources in early earth
- O2 is the most effiecetn electron acceptor due to high affinity for e-
Nitrate (NO3-)
describe nitrate respiration
- used as electron acceptor
- nitrate is reduced:
1. assimilative reduction = create oragnic compound
2. dissimiliative reduction = create energy - nitrate respiration: NO3 -> NO2 -> NO -> N20 -> N2
- enzymes reductases specific for each reaction
Nitrate (NO3-)
how is denitrification signifcant to agriculture
- detrimental for agriculture
- beneficial for sewage treament; reduce nitrate help in reomval in toxic nitrogen
Nitrate (NO3-)
what is the eukaryotic example of denitrification
- BENTHIC FORAMINIFER
- store large amounts of nitrate inside the cell
- produce N2 from NO3-
- denitrification takes place in the mitochondria
- no oxygen but they still live
Nitrate (NO3-)
example of denitrifying fungi
- FUSARIUM OXYSPORUM
- facultative anaeorbic organism; no O2 available (hypoxia) use nitrate as alternative
- nitrate converted to N2O
- simultaneously, they can still use O2
- called hybrid respiration; both processes occur in mitochondria
Nitrite (NO2-)
what are the two organisms that perform nitrite reduction and explain them
- Anammox (Brocadia anammoxidans)
- Candidatus (Methylomirabilis oxyfera)
- Methane (CH4) energy source and NO2- respiration (reduced) = N2 and O2
- O2 used to activate methane (CH4) oxidation
- belonds to NC10 Phylum of Bacteria
Sulfate Reduction
explain sulfate reduction placement in the tower of power
- SRB have short ETC
- to respire sulfate, the fuel source must be highly energetic
- organic substrates and H2 are above sulfate
Sulfate Reduction
What are the characteristics of SRBS
- energy source is organic or H2
- Sulfate SO42- is respired
- H2S is produced (used by colorless sulfur bacteria and anoxygenic phototrophs)
- compete with methogens for H2 as a fuel source
- assimilative - to satisfy suluf needs in the organisms
- dissimilatroy - create H2S
Sulfate Reduction
Explain the ancient process for detoxification
- add iron (Fe3+) in the area with suldifogenesis
- H2S reacts with ferric iron (Fe3+) and formas FeS2(pyrite)
Sulfate Reduction
how does corrosion occur
- microbes consume O2 at the metal surface; becomes depleted (anaerobic)
- SRB occupy space; creates H2S
- H2S reacts with metals forming metal-sulfides
- metal sulfies create corrosions
- coating constructions to prevent microbial biofilms
Sulfate Reduction
Describe the oragnic sulfur cycle in the ocean
- DMSP molecule made by marine algae
- DMSP degraded by mircoorganisms to create DMS
- DMS can be electron donor; photooxidation creates aerosols with SO2 SO42- and methane, sulfonate
- these compounds contribute to global cooling
Sulfate Reduction
what is the symbiosis b/w ANME and SRB
- Anaerobic methan-oxidizing archaea (ANME)
- uses methan as energy source and repsire sulate
- SRB creates energy while respitiring sulfate and makes NADH which is used by ANME
- reaction is not very energetically favourable but it is still occuring
CO2 as an electron acceptor
explain acetogenesis
2 important enzymes
- acetogens
- H2 is energy source
- CO2 is respired
- Acetate is excreted
- Hydrogenanse; extracts energy from H2 fuel that helps in CO2 fixation
- CO dehydrogenase; reduces fixed CO2 and create acetate
CO2 as an electron acceptor
explain methanogensis
- consume H2 and CO2
- compete with acetogens for H2
- generate methane; which is consumed in oxic systems by methanotrophs
- ARE ARCHAEA
what are other electron acceptors
4 others, explain first, two famous iron reducers
- metals, metalloids, halogenated organic compounds, unhalogenated oragnic compounds
METAL REDUCTION - ferric iron (Fe3+) and manganic ion (Mn4+)
- use organice energy source and H2
- Fe 3+ reduced to Fe2+; Mn4+ reduced to 2+
- SHEWANELLA and GEOBACTER
Proton H+ reduction
explain proton reduction
name
- PYROCOCCUS FURIOSUS
- archaea that grows optimally at 100oC
- uses sugar and small peptides as fuel source
- pssoble beacuse of modified glycolytic pathway
what are some other inorganic substrate?
name
- sulfate reducing bacterium; DESULFOTOMACULUM performs asenate and sulfate reduction
- generates mineral As2S3 (orpiment)
