Introduction: Glycerol is a highly abundant organic compound in nature that many organisms utilize as carbon and energy source. However, although the genetic capacity to grow on glycerol was reported for several archaea [1] the glycerol degradation has so far only been reported for the halophile Haloferax volcanii [2].

Objective: In this study, the glycerol degradation in the thermoacidophilic crenarchaeal model organism Sulfolobus acidocaldarius was analyzed.

Methods: Growth experiments, polyomics as well as biochemical and deletion mutant analyses were applied to gain comprehensive insights into the underlying mechanisms.

Results: S. acidocaldarius grows on glycerol as sole carbon and energy source. Glycerol degradation proceeds via glycerol kinase (GK) mediated phosphorylation to glycerol-3-phosphate followed by oxidation to dihydroxyacetone phosphate (DHAP) catalyzed by an unusual quinone reducing FAD-dependent glycerol-3-phosphate dehydrogenase (G3PDH), which shows a novel mode of membrane associtation facilitated by a small, CoxG-like protein.

The S. acidocaldarius genome encodes both, GK and G3PDH, in two paralogous copies which were characterized and shown to be functionally similar. However, polyomics studies indicated that only one of these GK-G3PDH couples is upregulated in presence of glycerol. Accordingly, deletion of the respective GK abolished growth on glycerol and crude extract measurements displayed an almost complete loss of GK activity. In contrast, deletion of the second GK led only to slightly diminished growth on glycerol and no significant change in GK activity in crude extracts. Thus, only one of the two GK-G3PDH couples is essential to maintain growth on glycerol.

Summary: We herein unraveled the glycerol degradation in the crenarchaeon S. acidocaldarius to proceed via the GK-G3PDH pathway involving a "classical" GK and an unusual G3PDH which differs in structure and membrane association from those known in bacteria and haloarchaea.

References

Villanueva L et al. (2017), Environ Microbiol, 19(1):54-69.Sherwood KEet al. (2009). J Bacteriol, 191(13):4307-4315.