AN INTRODUCTION TO ARCHAEA

 ARCHAEA

·       Prokaryotic in nature.

·   The word Archaea is derived from the Greek word Archaios, meaning “Ancient” or “Primitive,” and indeed some archaea exhibit characteristics worthy of that name.

·       In 1977, Carl Woese and George Fox recognized that the Archaea have a separate line of evolutionary descent from bacteria in phylogenetic tree based on the sequencing of 16S Ribosomal RNA (rRNA), and divided prokaryotes into two evolutionary domains (Bacteria & Archaea), as part of the Three - domain system.

·       Unicellular in nature.

·       Measured in micrometer (µm) and Size was ranged from 0.1 µm to 15 µm.

·   Shape range - Spherical, rod-like, spiral, plates, irregularly shaped, lobed, needle-like filamentous, rectangular rods and flat square shape.

·   Cell wall is made up of Polymers other than Peptidoglycan. Because of this reason, Archaea was differentiated from Bacteria by Carl Woese and George Fox. Therefore, the absence or presence of Peptidoglycan is a distinguishing feature between the Archaea and Bacteria.

·       Reproduction – Asexual reproduction is the only way for archaea. They reproduce asexually via Binary fission, Budding, or Fragmentation.

·       No Archaeal member has been reported to undergo Endospore formation.

·       Locomotion – Flagella. Some are motile and few are non – motile.

·       Non – Pathogenic.

Members of Archaea

·    Members of the archaea includes Methanogens (used for Biogas production and Sewage treatment), Extreme acidophiles (lives in high acidic concentration), Extreme halophiles (lives in high salt concentration) and Extreme thermophiles (lives in high temperature).

ü  Pyrolobus fumarii, which holds the upper temperature limit for life at 113 °C (235 °F) and was found living in hydrothermal vents.

ü  Species of Picrophilus, which were isolated from acidic soils in Japan and are the most acid-tolerant organisms capable of growth at around pH 0.

ü  Halophiles, including the genus Halobacterium, survive in hypersaline environments such as salt lakes, and can outcompete bacterial counterparts at salinities greater than 20 %.

ü  The methanogens, which produce methane gas as a metabolic by-product and are found in anaerobic environments, such as in marshes, hot springs, and the guts of animals, including humans.

Habitat of Archaea

·       Archaea are microorganisms that define the limits of life on Earth.

·       Archaea were originally discovered and described in extreme environments, such as hydrothermal vents and terrestrial hot springs.

·       Archaea were also found in a diverse range of highly saline, acidic, and anaerobic environments.

·       Archaeal Groups Inhabiting Different Extreme Habitats. They are

a)     Halophiles - Live in extreme salt conditions like salt lakes, and brackish waters. Example: Halobacterium spp.

b)     Thermophiles - Live in extremely high temperatures like hot springs and vents. Example: Methanopyrus kandleri.

c)     Alkaliphiles - Live in extreme alkaline conditions like marine hydrothermal systems. Example - Thermococcus alcaliphilus is a marine Archaea.

d)     Acidophiles - Live in extremely acidic conditions like dry hot soil and volcanic sites. Example - Picrophilus torridus.

Mode of Nutrition in Archaea

·    Based on their preference of source for deriving energy, they are divided into different nutritional groups. Some of them are:

a)     Phototrophic Archaea: Some species of archaea are known to utilize energy from the sun. Hence, they are called Phototrophic archaea. Although, they can utilize sunlight like the plants, they cannot fix atmospheric carbon. So, they are “Phototrophic” and “Not Photosynthetic”. Example – Haloarchaea sp. or Halobacterium sp.

b)     Lithotrophic Archaea: Some species of Archaea are known to utilize inorganic compounds (Chemical energy) to take care of their energy needs like metal ions, hydrogen, ammonia, etc. Examples - Pyrolobus, Ferroglobus, Methanobacteria, Ammonia oxidizing archaea and Sulfate reducing archaea.

c)     Organotrophic Archaea: Some species of Archaea are known to utilize organic compounds to take care of their energy needs like pyruvate, starch, maltose, etc. Examples – Methanosarcinales sp., Pyrococcus sp. and Sulfolobus sp.

Association between Archaea and Eukaryotes

·       Archaea are also found living in association with eukaryotes.

·    For example, Methanogenic archaea are present in the digestive systems of some animals, including humans.

·       Some archaea form symbiotic relationships with Maine sponges.