Fundamentals of Microbiology

4.5.1 Bacteria of extreme environment

Pokaryotes are known to thrive in harsh environments where other eukaryotes do not exist.

Extreme halophiles

Prokaryotes that inhabit highly saline environments such as salt pans and natural salt lakes or heavily salted foods are called extreme halophiles. Theses organisms require 1.5 to 4M (9-23%) NaCl for optimal growth, and can grow up to the limit of saturation of NaCl (32%). Extreme halophiles belong to Archaea and are collectively called halobacteria. Examples are Halobacterium. Halobacterium sp. are well adopted to saline environments. The cell wall is stabilized by sodium ions. Na⁺ binds to the outer surface of the well thus maintaining cellular integrity. Further cells of Halobacterium pump large amounts of K⁺ from the environment into the cell to counter the Na⁺ outside cell, thereby remain in positive water balance. The cell wall is made up of glycoprotein which has high content of acidic amino acids. The cytoplasmic proteins are also highly acidic and contain low levels of hydrophobic amino acids. All extremely halophilic Archaea are chemo-organotrophs and most of them are obligate aerobes.