It has been observed that
‘all cells’
eukaryotes,
and the prokaryotes. Besides, the multicellular plants and animals are invariably eukaryotic
in nature and character, and so are the numerous
unicellular organisms. The only prokaryotes are the
organisms, such as :
cyanobacteria (Gr. hyanos = dark blue). In the recent past this very classification
has undergone a considerable change. It has been duly established and observed that there exists another
‘group of organisms’
amongst the bacteria that do not seem to fall into either of the two aforesaid
categories. These organisms have been termed as the
archaeobacteria, which essentially designate an
altogether new primary kingdom having an entirely different status in the history and the natural order of life.
The enormous volume of informations based on experimental evidences gathered from studies
of
ribosomal RNA suggests that archaeobacteria and eubacteria strategically got separated at a very
early stage in the pioneer process of evolution of life on this planet (earth). Importantly, the
phylogenetic*
distance that critically prevails between the
two above mentioned categories of bacteria is reflected bysome phenotypic** differences prominently,
Archaeobacteria,
in reality, do not represent a perfect homogeneous group. One may, however,
observe a substantial degree of heterogeneity amongst the
eubacteria, so do the different types of
archaeobacteria
specifically differ from each other with respect to morphology, metabolism, chemicalcomposition, and habitat.
The
‘archaeobacteria’ are unusual organisms by nature, and this particular category is known to
comprise essentially of
three different types of bacteria, namely :
(
a) Methanogenic bacteria,
(
b) Extreme halophiles, and
(
c) ThermoacidophilesThese three groups of organisms shall now be treated individually in the sections that follows :