Piezophiles Flashcards
How are piezophiles isolated
Specifically designed pressurised chambers were constructed to bring samples to the surface and act as growth chambers on the research vessel or later in the laboratory (the DEEPBATH system)
Key for deep sea sampling, retrieving, isolation and cultivation are the following four constrains: isopiestic, isothermal, dark and axenic.
How are piezophiles classified
- piezotolerant - grow up to 50 MPa, but optimum growth at atmospheric pressure (0.1 MPa)
- Piezophilic - grow optimally between 10-50 MPa
- Hyperpiezophilic - optimum growth at > 50 MPa
Examples of piezophiles
Psychrophilic piezophiles are mainly gram- negative bacteria, 5 main genera all belonging to gamma-proteobacteria
Shewanella, photobacterium, Colwelliam Moritella and Psychromonas
hermophilic piezophiles include both Bacteria and Archaea e.g. Marinitoga piezophila – a sulphate reducing bacterium.
All hyperthermophile piezophiles are archaea e.g. Pyrococcus abyssi.
Methanopyrus kandleri strain 116 grows optimally at 105oC and 20-30 MPa. At 40 Mpa (400 atm), it can grow at 122oC – new temperature record.
Cultivation of Piezophiles
The use of rich media favouring growth of heterotrophs has biased the isolation of piezophiles in favour of Gram–negative bacteria such as Shewanella.
More use of minimal media that more closely mimic the chemical composition of natural piezophile habitats will lead to a wider diversity of organisms being isolated. However, cultivation takes time due to very slow doubling times
Pressure Limit of Piezophiles
Highest hydrostatic pressure which will support growth is 130MPa = 1300atm = 13 km depth.
No part of the deep ocean is known to reach 13km, but greater lithostatic pressures will exist deeper within the Earth’s crust.
Molecular Adaptations to high Pressure: Ribosomes
Helices 10 and 11 interact with S20 protein, which is essential for correct ribosome assembly.
Inability to form functional ribosomes has been seen to stop growth of non-piezophiles at high pressure.
Therefore, it appears that the elongated loops are a modification to allow ribosomal 30S and 50S subunits to associate at high pressures and form a functional ribosome.
Stem loop structure: lots of genetic variability. Correlates with the occurence of different habitats
Elongation of stem structures play a role of increasing pressure- long stems- interaction of the subunits and the integrity
Molecular Adaptations to high Pressure:
Lipids
Piezophilic psychrophilic bacteria synthesise long chain omega-3 polyunsaturated fatty acids i.e. eicosapentaenoic acid (EPA 20:5) and docosahexaenoic acid (DHA 22:6). Increasing pressure can lead to 70% of the total fatty acids being unsaturated.
In addition to fatty acid synthase (FAS) pathway, piezophiles also have polyketide synthase (PKS) pathway which is responsible for producing the EPA (precursor - synthesised through sequential process) and DHA- primary compound for unsaturated fatty acids in the human brain- used for baby formula
In addition, the lipid head group (larger and differently shaped- disrupt) phosphatidylglycerol is favoured by psychrophilic piezophiles over phosphatidyl-ethanolamine - multi module proteins that can become large- they can combine nodules and do synthesis steps- in large secondary metabolites- long double bond containing heterocyclic structures.
Molecular Adaptations to high Pressure:
Proteins
A comparison of proteins from two hyperthermophilic Pyrococcus species was done – P. furiosus is a non-piezophile (isolated at 0.5 m depth) and P. abyssi is a piezophile (isolated at 2000 m depth).
The key difference in the piezophile was the increased abundance of small size amino acids such as serine and glycine- also have to be more flexible in the enzymatic centre- lowering of temperature in these depths
