The
thermoacidophiles
by a remarkable tendency and capability to attain growth not only under
extremely high acidic
conditions,
but also at considerably elevated temperatures.
There are
two most prominent genera that belong to this particular category, namely :
(
a) Thermoplasma, and
(
b) Sulfolobus.
2.5.3.1 Thermoplasma
These chemoorganotrophic microorganisms very much look alike the
mycoplasm (i.e., a group
of organisms that lack cell walls and are highly pleomorphic), and obviously varying from spherical in
shape to filamentous in nature. The ideal and optimum temperature for their progressive growth ranges
between 55 and 59 °C (minimum, 44 °C ; maximum, 62 °C), whereas the optimum pH is 2 (minimum, 1 ;
maximum, 4). It has been duly observed that the cells of these
thermoplasmas undergo abundant lysis
virtually at a neutral pH. In actual practice, the
thermoplasmas have been duly isolated from the residual
heaps of burning coal refuse.
2.5.3.2 Sulfolobus
The cells of this particular genus are more or less lobe-shaped or spherical in shape and appearance.
They have the definite cell walls that are essentially made up of protein. However, the
optimumtemperature and optimum pH of different species of sulfolobus are as given below :
Optimum temperature : 70–87 °C ;
Optimum pH : 2 [Min. 1 ; Max. 4].
Nevertheless, the
sulfolobus are established to be autotrophic* facultatively. In fact, sulfolobus
may be grown in
two different manners as stated under :
Method ‘A’
— as ‘chemolithotrophs’ when adequately provided with ‘S’ as an element and an
electron donor, and
Method ‘B’
— as ‘chemoorganotrophs’ in the respective media comprising of organic substrates.
Interestingly, the natural occurrence of the
sulfolobus species are prominently and predominentlyfound in sulphur (acidic) hot springs around the world.