title: Glutamate and histidine improve both solvent yields and the acid tolerance response of Clostridium beijerinckii NCP 260.
abstract: OBJECTIVE
  This study aims to examine the effect of amino acid supplementation on solvent production by Clostridium beijerinckii during the acetone-butanol fermentation and to determine whether amino acids are involved in the acid tolerance response (ATR), which results in increased solvents.
  
  
  RESULTS
  Fermentation studies with Cl. beijerinckii NCP 260 in limited-nitrogen media supplemented with glutamate, glutamine, lysine, proline, histidine or asparagine revealed that only glutamate, glutamine or histidine increased butanol titres comparable to control media. Acid survival tests at pH 5 showed that glutamate and histidine were effective in protecting Cl. beijerinckii cells against acid shock, and may be involved in the ATR. Using quantitative PCR, the transcription of the glutamine synthetase, nitrogen regulator and glutamate synthase operon (glnA-nitR-gltAB) was monitored during acid shock conditions, and expression of both the nitR and gltA genes was shown to be increased twofold.
  
  
  CONCLUSIONS
  Glutamate and histidine specifically enhance the ATR in Cl. beijerinckii NCP 260, and the genes encoding glutamate synthase and the NitR regulator are both upregulated, predicted to lead to increased endogenous glutamate pools during acidogenesis. This may enhance the ATR and allow more viable cells to enter solventogenesis, thereby increasing butanol titres. Glutamine, glutamate and histidine may also afford protection from butanol stress directly.
  
  
  CONCLUSIONS
  Using substrates naturally rich in glutamine, glutamate and histidine in industrial fermentations is a promising means to increase acid survival and solvent yields in solventogenic Clostridium.
authors.affiliation: University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: B W P
authors.initials: BW
authors.lastname: Reeve
authors.affiliation: University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: S J
authors.initials: SJ
authors.lastname: Reid
mesh_terms: D000096:Acetone / Q000378:metabolism; D000596:Amino Acids / Q000494:pharmacology; D000440:Butanols / Q000378:metabolism; D046970:Clostridium beijerinckii / Q000378:metabolism*; D005285:Fermentation; D005809:Genes, Regulator; D005970:Glutamate Synthase / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology*; D006639:Histidine / Q000494:pharmacology*; D012997:Solvents / Q000378:metabolism; D013312:Stress, Physiological
chemical_list: D000596:Amino Acids; D000440:Butanols; D012997:Solvents; D000096:Acetone; D018698:Glutamic Acid; D006639:Histidine; D005970:Glutamate Synthase
keywords: ABE fermentation; acid tolerance response; biobutanol; glutamate; histidine; nitrogen metabolism