Practice question

Among prokaryotes, membrane-spanning tetraether lipids represent adaptation to extreme temperature and acidity not found in mesophilic bacteria like Escherichia coli, Mycobacterium tuberculosis, or Bacillus subtilis that maintain bilayer of diester or diether lipids. Sulfolobus acidocaldarius, an aerobic thermoacidophile isolated from solfataric hot springs growing optimally at 80 degrees Celsius and pH 2 to 3, synthesizes predominantly glycerol dibiphytanyl glycerol tetraethers (GDGTs) composed of two C40 isoprenoid chains linking two glycerol moieties via ether bonds, creating monolayer membrane where each molecule spans entire membrane thickness. These bolaamphiphiles may contain cyclopentane rings increasing packing tightness and reducing permeability to protons, essential for maintaining pH gradient despite external acidity. Additional modifications like calditol headgroups enhance acid resistance. Escherichia coli uses phosphatidylethanolamine esters, Mycobacterium uses mycolic acid rich outer membrane, Bacillus uses typical ester bilayer. Therefore tetraether monolayer is diagnostic for extreme thermoacidophilic archaea exemplified by Sulfolobus genus within Crenarchaeota and orders Sulfolobales. This mechanistic insight is relevant for competitive examinations such as CSIR-NET and GATE, where understanding molecular detail rather than memorization enables accurate interpretation of experimental data and pathway interconnections.