, Volume 137, Issue 4, pp 329-337

Fermentation of glutamate and other compounds by Acidaminobacter hydrogenoformans gen. nov. sp. nov., an obligate anaerobe isolated from black mud. Studies with pure cultures and mixed cultures with sulfate-reducing and methanogenic bacteria

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Abstract

From mud from the Ems-Dollard estuary (The Netherlands) an L-glutamate-fermenting bacterium was isolated. The isolated strain glu 65 is Gram-negative, rodshaped, obligately anaerobic, non-sporeforming and does not contain cytochromes. The G+C content of its DNA is 48 mol percent.

Pure cultures of strain glu 65 grew slowly on glutamate (μmax 0.06 h-1) and formed acetate, CO2, formate and hydrogen, and minor amounts of propionate. A more rapid fermentation of glutamate was achieved in mixed cultures with sulfate-reducing bacteria (Desulfovibrio HL21 or Desulfobulbus propionicus) or methanogens (Methanospirillum hungatei or Methanobrevibacter arboriphilicus AZ). In mixed culture with Desulfovibrio HL21 a μmax of 0.10 h-1 was observed. With Desulfovibrio or the methanogens propionate was a major product (up to 0.47 mol per mol glutamate) in addition to acetate.

Extracts of glutamate-grown cells possessed high activities of 3-methylaspartase, a key enzyme of the mesaconate pathway leading to acetate, and very high activities of NAD+-dependent glutamate dehydrogenase, an enzyme most likely involved in the pathway to propionate.

The following other substrates allowed reasonable to good growth in pure culture: histidine, α-ketoglutarate, serine, cysteine, glycine, adenine, pyruvate, oxaloacetate and citrate. Utilization in mixed cultures was demonstrated for: glutamine, arginine, ornithine, threonine, lysine, alanine, valine, leucine and isoleucine (with Desulfovibrio HL21) and malate (with Methanospirillum).

The shift in the fermentation of glutamate and the syntrophic utilization of the above substrates are explained in terms of interspecies hydrogen transfer.

Strain glu 65 is described as the type strain of Acidaminobacter hydrogenoformans gen. nov. sp. nov.