References

Microbial Diversity in Soils 29
soil. Actinomycetes can be isolated in sufficient number even from the
C horizon (weathered parent material) of soil profiles. The commonest
genera of actinomycetes are Streptomyces (nearly 70%). In contrast, Nocardia
and Micromonspora and in particular, Actinomyces, Actinoplanes and
Streptosporangium are only encountered occasionally (Prescott et al. 1996;
Subba Rao 1997). Temperatures between 25 and 30 ◦ C are conducive for the
growth of actinomycetes although thermophilic cultures growing at 55 and
65 ◦ C are common in compost heaps where they are numerically extensive
and belong mostly to the genera Thermoactinomyces and Streptomyces.
3.2
Archaebacteria
Archaebacteria is a group of primitive prokaryotes, which were the earliest
organisms to have appeared on the earth. Therefore, they are called the
ancient bacteria. They even live in extreme hostile environments, like salt
Table 4. Diversity of archaebacteria
Archaebacteria Characteristics
Methanogens
Methanococcus, Methanosprillum
Extreme halophiles
Halobacterium, Halorubrum, Natrinobacterium,
Natronococcus
Methane-generating thermophiles
Methanothermus
Sulfur- and sulfate-reducing hyperthermophiles
Thermococcus, Archaeoglobus, Thermoproteus,
Pyrodictium, Pyrolobus
Sulfer oxidizers
Sulfolobus
Thermophilic extreme acidophiles
Thermophilus, Picrophilus
Generate methane when they oxide
hydrogengasasanenergysource,using
CO2 as a terminal electron acceptor
Found near salt lakes, soda lakes, and
brines. They produce pigments and can
be seen as pink blooms in concentrated
saltwater ponds
Found near hydrothermal vents; can grow
at temperatures near 100 ◦ C
Obligate anaerobes that use sulfur or sulfate
as a terminal electron acceptor, generating
hydrogen sulfide. Thermococcus, and
Archaeoglobus oxidize organic compounds
as an energy source; Thermoproteus,
Pyrodictium, andPyrolobus oxidize H2 as
an energy source
Oxidize sulfur as a source of energy, using
O2 as a terminal electron acceptor to
generate sulfuric acid
Grow only in extremely hot, acid
environments