Elucidation of the pathways of catabolic glutamate conversion in three thermophilic anaerobic bacteria.
The glutamate catabolism of three thermophilic syntrophic anaerobes was compared based on the combined use of [(13)C] glutamate NMR measurements and enzyme activity determinations. In some cases the uptake of intermediates from different pathways was studied. The three organisms, Caloramator coolhaasii, Thermanaerovibrio acidaminovorans and strain TGO, had a different stoichiometry of glutamate conversion and were dependent on the presence of a hydrogen scavenger (Methanobacterium thermoautotrophicum Z245) to a different degree for their growth. C. coolhaasii formed acetate, CO(2), NH(4)(+) and H(2) from glutamate. Acetate was found to be formed through the beta-methylaspartate pathway in pure culture as well as in coculture. T. acidaminovorans converted glutamate to acetate, propionate, CO(2), NH(4)(+) and H(2). Most likely, this organism uses the beta-methylaspartate pathway for acetate formation. Propionate formation occurred through a direct oxidation of glutamate via succinyl-CoA and methylmalonyl-CoA. The metabolism of T. acidaminovorans shifted in favour of propionate formation when grown in coculture with the methanogen, but this did not lead to the use of a different glutamate degradation pathway. Strain TGO, an obligate syntrophic glutamate-degrading organism, formed propionate, traces of succinate, CO(2), NH(4)(+) and H(2). Glutamate was converted to propionate oxidatively via the intermediates succinyl-CoA and methylmalonyl-CoA. A minor part of the succinyl-CoA was converted to succinate and excreted.
Plugge
C M
CM
Laboratory of Microbiology, Wageningen University, H. van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands. caroline.plugge@algemeen.micr.wag-ur.nl
van Leeuwen
J M
JM
Hummelen
T
T
Balk
M
M
Stams
A J
AJ
D000693:Anaerobiosis; D001421:Bacteria, Anaerobic / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism*; D005971:Glutamates / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy
D005971:Glutamates