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Background  Glycerol has enhanced its biotechnological importance since it is a byproduct of biodiesel synthesis. A study of  Escherichia coli  physiology during growth on glycerol was performed combining transcriptional-proteomic analysis as well as kinetic and stoichiometric evaluations in the strain JM101 and certain derivatives with important inactivated genes.    Results  Transcriptional and proteomic analysis of metabolic central genes of strain JM101 growing on glycerol, revealed important changes not only in the synthesis of MglB, LamB and MalE proteins, but also in the overexpression of carbon scavenging genes:  lamB ,  malE ,  mglB ,  mglC ,  galP  and  glk  and some members of the RpoS regulon ( pfkA ,  pfkB ,  fbaA ,  fbaB ,  pgi, poxB ,  acs ,  actP  and  acnA ). Inactivation of  rpoS  had an important effect on stoichiometric parameters and growth adaptation on glycerol. The observed overexpression of  poxB ,  pta ,  acs  genes, glyoxylate shunt genes ( aceA, aceB ,  glcB  and  glcC ) and  actP , suggested a possible carbon flux deviation into the PoxB, Acs and glyoxylate shunt. In this scenario acetate synthesized from pyruvate with PoxB was apparently reutilized via Acs and the glyoxylate shunt enzymes. In agreement, no acetate was detected when growing on glycerol, this strain was also capable of glycerol and acetate coutilization when growing in mineral media and derivatives carrying inactivated  poxB  or  pckA  genes, accumulated acetate. Tryptophanase A (TnaA) was synthesized at high levels and indole was produced by this enzyme, in strain JM101 growing on glycerol. Additionally, in the isogenic derivative with the inactivated  tnaA  gene, no indole was detected and acetate and lactate were accumulated. A high efficiency aromatic compounds production capability was detected in JM101 carrying pJLB aroG   fbr   tktA , when growing on glycerol, as compared to glucose.    Conclusions  The overexpression of several carbon scavenging, acetate metabolism genes and the absence of acetate accumulation occurred in JM101 cultures growing on glycerol. To explain these results it is proposed that in addition to the glycolytic metabolism, a gluconeogenic carbon recycling process that involves acetate is occurring simultaneously in this strain when growing on glycerol. Carbon flux from glycerol can be efficiently redirected in JM101 strain into the aromatic pathway using appropriate tools.

New insights into Escherichia coli metabolism: carbon scavenging, acetate metabolism and carbon recycling responses during growth on glycerol