Polyextremophiles Flashcards
What are polyextremophiles
Organisms that can adapt and grow in the presence of two or more environmental extremes are called polyextremophiles e.g.
Haloalkaliphiles (soda lakes)
Thermoacidophiles (acidic hot springs)
Halopsychrophiles (sea ice)
Haloalkaliphiles
Soda lakes are highly productive environments despite requiring microbes to cope with high salinity and high pH. Total bacterial and archaeal diversity in low saline lakes (35-50g/l) can be as high as in fresh water lakes
Their productivity is at least partly due to blooms of cyanobacteria (including N2 fixing species).
The salinities of soda lakes vary dramatically from total salt equivalent to 0.8 M NaCl up to saturated salt conditions (equivalent to 5.5 M NaCl).
Examples of Haloalkaliphiles
A variety of pH and salinity conditions are found in soda lakes and even adjacent lakes can differ dramatically. Therefore, particular soda lakes favour particular bacteria. Each lake usually have different populations of bacteria
Several well known genera of bacteria are found in soda lakes e.g. the cyanobacterium Spirulina platensis (optimum growth at pH 10, but will not grow much above 1 M NaCl) and the Gram-negative denitrifying bacterium Halomonas campisalis (growth up to 4 M NaCl and pH 11).
New and unusual Examples of Haloalkaliphiles
Alkalimonas spp. – one species from Mongolia, the other from the Rift Valley, only slightly halophilic, but optimum growth at pH 10.
Dietzia natronolimnaea – Rift Valley soda lake, pH optimum is 9, but grows well from pH 6 to 10. It is essentially halotolerant, only requires NaCl for growth above pH 7.
Natronobacterium – Rift Valley – genus of Halobacteriaceae (Archaea), extreme halophile and alkaliphile.
Thermoacidophiles
Thermoplasma acidophilum is an archaeon that lacks a cell wall and its cytoplasmic membrane has to restrict entry of H+. It grows optimal at 56 oC and pH 1.8.
Since thermal acidic environments were probably common on the early Earth, T. acidophilum (helped in the structural deciphering in the proteosome) may be closely related to very ancient organisms. Proteasome is made out of 4 identical rings- each ring is made from 7 identical subunits- differ in composition e.g. 2 rings.
Variable in their shape- look a rod shaped bacteria to spindle forms- structure is in part determined by the s layer- can lead to different versions.
Protons become a problem at low pH
Examples of Thermoacidophiles
Thermoplasma acidophilum, rotary shadowing of the irregularly shaped cells.
Ferroplasma acidarmanus also lacks a cell wall and grows optimally at pH 1.2, with growth still occurring at pH 0.
Halopsychrophiles
Sea ice is found in polar regions and in Baltic and Caspian Seas – it is seasonal, but can cover millions of square kilometres.
Sea ice is semi-solid with a network of channels which can be as small as few micrometers. The channels are full of highly saline brine.
Diffusion rates of gases and nutrients are low.
Temperatures reach as low as -20°Cand extreme salt tolerance is required in the brine (salinity is ca. three times that of seawater) and during melting of the ice hyposaline conditions close to freshwater occur
What compatible solute do halopsychrophiles use
dimethylsulfoniopropionate (DMSP) as a compatible solute and cryoprotectant. DMSP is a precursor of dimethyl sulphide (DMS) – volatile and involved in cloud formation.
