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Summary Theme 7 MBY251 study notes
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THEME 7 – ECOLOGICAL AND FUNCTIONDIVERSITY
Terminology:
- Lineage: descent/ ancestry
- Phylum: a major lineage in one of the three domains of life
- Phylogeny: evolutionary history of and organism
- Ecology: relationship of an organism w/ its environment
- Physiology: functions and processes allowing an organism to grow and multiply
- Adaptation: processes allowing an organism to become better suited for living in its environment
- Anaerobic respiration: a form of respiration in which the electron acceptor is not oxygen
- Aerobic respiration: respiration that requires oxygen
- Oxygenic photosynthesis: photosynthesis in which oxygen is produced
- Anoxygenic photosynthesis: photosynthesis which does not produce oxygen
- Enrichment media: media that favour growth of certain bacteria
Microbial diversity
- Metabolic diversity: defined in terms of cellular processes supporting growth (N
fixing, iron oxidisers)
- Phylogenetic diversity: defined by evolutionary relationships btw organisms (defined
by 16s ribosomal RNA phylogeny
- Ecological diversity: defined in terms of microbial interactions btw organisms and
their environment
Factors driving microbial diversity
At least 3 reasons metabolic/ecological traits are shared by divergent organisms
1. Gene loss: a trait present in a common ancestor is lost during divergence
2. Convergent evolution: a trait has evolved independently in 2+ lineages and is not coded by homologous
genes
3. Horizontal gene transfer: genes that code for a trait are homologous and have been exchanged btw distant
related lineages
Ecological diversity
Phototrophic - oxy and anoxy
- Able to conserve energy from light evolved early when earth was anoxic
- Photosynthesis started w/ bacteria
- 1st photo = anoxygenic (don’t generate O2, used H2 instead of H2O)
- extensively diverse amongst anoxygenic
- common features:
chlorophyll like pigments to harvest energy to drive e- transfer and produce ATP
pigments found in intracellular membrane systems (better use of light in low intensities)
not all fix carbon
2 types of reaction centres:
1. FeS in photosystem I of oxygenic photos
2. Q-type found in photosystem II of oxygenic photos
Both found in cyanobacteria
Oxygenic Cyanobacteria:
phototrophic Genera: Prochlorococcus, Trichodesmium
- 1st oxygen-evolving photo
- large, morphologically, ecologically heterogeneous group
- 0.5-100 μm diameter
- Morphological groups: unicellular/ filamentous
, - distant relative to gram (+)
General info:
• Chroococcales: unicellular, divide by binary fission
- Includes prochlorophytes (unique, unicellular)
• Pleurocapsales: unicellular, dividing by multiple fission (colonial)
• Oscillatoriales: filamentous nonheterocystous
• Nostocales: filamentous, divide on single axis, can differentiate
• Stigonematales: filamentous, divide in multiple planes, forming branching filaments
Physiology & photosynthetic membranes
- Oxy photos w/ FeS and Q-type photosystems
- all fix CO2 by Calvin cycle
- many fix N2
- most synthesise own vitamins
- harvest energy from light and fix CO2 during day
- generate energy by fermentation/ aerobic respiration of stored C products
Thylakoids: specialised membrane systems that increase ability to harvest light energy, typically
arranged in concentric circles around cytoplasm periphery
-- produce pigments (chlorophyll a and phycobilin’s)
Physiology: germination and vegetative growth
Some form akinetes (resting structure w/ thickened outer walls to protect from darkness,
desiccation, or cold)
Physiology and motility:
- motility mechanisms but NO flagella
- Gliding motility when in contact w/ solid surface, another cell/ filament
- some form hormogonia (short, motile fragments, break off to disperse under stress)
show phototaxis, sometimes chemo
- gas vesicles (regulate buoyancy), for positioning in water column where low light intensity
N fixation
- many form cyanophycin (N storage product, N rich reserve)
- Nitrogenase is O sensitive, so cant occur w/ oxygenic photosynthesis
- 3 mechanism to separate Nitrogenase from photosynthesis
1. many unicellular ONLY fix at NIGHT
2. some suppress photosynthetic activity w/in filaments
3. many filamentous form heterocyst’s
- arise from differentiation of vegetative cells
- surrounded by thickened cell wall that slows diffusion of O2 (anoxic environment)
Ecology:
- NB for ocean productivity
-- most abundant ocean phototrophs (contribute to 80% of marine photosynthesis)
- dominant input of new N in oceans
- terrestrial and freshwater too:
--more tolerant that algae
--develop freshwater lake blooms
--can be symbionts (w/ ferns and cycads)
Anoxygenic Purple sulfur
Genera: Chromatium, Thermochromatium
- use Hydrogen sulfide (H2S) as e- donor for photosynthesis
- found in anoxic zones where H2S is found (lakes, marine sediments)
- members in Gammaproteobacteria
- purple colour from carotenoids (accessory pigment to harvest light)
- use Q-type photosystem and fix carbon in Calvin cycle
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