The Adaptation of Archaea to Acidity

The adaptation of archaea in acidic condition. How archaea adapt to acidic environment ? Use variety pH homeostatic mechanism that involve restricting proton entry by cytoplasmic membrane and purging of protons and their effect by cytoplasm. pH homeostatic mechanisms The cell membrane is highly impermeable to protons Membrane channel have a reduced pore size. Protein influx inhibited by chemiosmotic gradient Excess proton pumped out of the cell Cytoplasmic buffering helps to maintain the intracellular pH 1.

The cell membrane is highly impermeable to protons High impermeable cell membrane to restrict proton influx into the cytoplasm Example : Archaeal-specific structures composed of tetraether lipids . Thermoplasma acidophilum, Ferroplasma acidiphilum, sulfolobus solfataricus. Factor causing low permeability of acidophile membranes. Monolayer composed of unique “tetraether lipids” in which two hydrophilic heads attached to the same hydrophobic tail through ether bonds – more stable, less fluid

Bulky isoprenoid core. Ether linkage characteristic of these membranes less sensative to acid hydrolysis than ester linkage. 2. Membrane channel have a reduced pore size. Control size of the entrance to the pore and the ion selectivity at the porin entrance. Control influx of proton across the outer membrane 3. Protein influx inhibited by chemiosmotic gradient Inhibit the influx of protons using a chemiosmotic barrier against the proton gradient (higher ? lower)

Chemiosmosis : diffusion of hydrogen ion across the biological membrane via transport protein due to a proton gradient that form on the other side of the membrane. 4. Excess proton pumped out of the cell Active proton pumping Remove excess protons from cytoplasm and balance the pH value in cell. Sequences acidophile genomes have proton efflux systems. 5. Cytoplasmic buffering helps to maintain the intracellular pH Intracellular mechanism help to improve the ensuing biological damage.

Cytoplasmic buffer molecules that have basic amino acids capable of sequestering protons. Thus maintain the pH in cytoplasm. References 1. D. B. Johnson, K. B. Hallberg The microbiology of acidic mine waters Res. Microbiol. , 154 (2003), pp. 466–473 2. G. K. Druschel et al. Acid mine drainage biogeochemistry at Iron Mountain California. Geochem. Trans. , 5 (2004), pp. 13–32 3. T. Rohwerder et al. Bioleaching review part A. Progress in bioleaching: fundamentals and mechanisms of bacterial metal sulfide oxidation Appl. Microbiol. Biotechnol. , 63 (2003), pp. 239–248