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MPI für Biochemie  

Membrane Biochemistry
Dieter Oesterhelt

Halobacterium bioenergetics

 

The bioenergetics of Halobacterium

The department is interested in the bioenergetics of Halobacterium salinarum.

Halobacterium can live under four bioenergetic regimes

  • aerobic respiration

    • Halobacterium metabolizes several amino acids and other carbon compounds but cannot live on glucose

    • Many of the metabolites are fed into pyruvate and then via acetyl-CoA into the TCA cycle

    • Halobacterium contains a complete respiratory chain

      • NADH is, however, not oxidized via complex I but via type II NADH dehydrogenase

      • More then 10 genes for complex I are encoded in the genome but its substrate is yet unknown

      • Halobacterium uses the copper protein halocyanin rather than cytochrome-c as substrate for complex IV

  • anaerobic respiration

    • Halobacterium can use organic compounds like DMSO as terminal electron acceptor under anaerobic conditions.

  • arginine fermentation

    • Arginine  fermentation by the ADI pathway (arginine deiminase pathway) allows ATP production. Arginine is converted to citrulline, which is split into ornithine and carbamoyl-phosphate. Carbamoyl-phosphate can be split into CO2 and NH3, the energy being used to produce one ATP molecule.

  • photosynthesis

    • Halobacterium can grow phototrophically with light as only energy source. Phototrophic growth occurs under anaerobic conditions. The retinal-based photosynthetic system of Halobacterium consists of the light-driven proton pump bacteriorhodopsin and ATP synthase.

  • evergy storage via ion gradients (a potassium battery)

    • When energy is amply availiable (e.g. when growing phototrophically), Halobacterium generates ion gradients. Commonly, the cytosol has 2M sodium and 2M potassion. Halobacterium can increase the internal potassium concentration up to 4M with concomitant reduction of the sodium concentration, resulting from a sodium/potassium exchange system. The resulting potassium gradient allows to maintain rather high internal ATP concentrations even in the absence of other sources of energy.