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

• Main Authors: Martínez-Gómez Karla, Flores Noemí, Castañeda Héctor M, Martínez-Batallar Gabriel, Hernández-Chávez Georgina, Ramírez Octavio T, Gosset Guillermo, Encarnación Sergio, Bolivar Francisco
• Format: Article
• Language: English
• Published: BMC 2012-07-01
• Series: Microbial Cell Factories
• Online Access: http://www.microbialcellfactories.com/11/1/46

<p>Abstract</p> <p>Background</p> <p>Glycerol has enhanced its biotechnological importance since it is a byproduct of biodiesel synthesis. A study of <it>Escherichia coli</it> 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.</p> <p>Results</p> <p>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: <it>lamB</it>, <it>malE</it>, <it>mglB</it>, <it>mglC</it>, <it>galP</it> and <it>glk</it> and some members of the RpoS regulon (<it>pfkA</it>, <it>pfkB</it>, <it>fbaA</it>, <it>fbaB</it>, <it>pgi, poxB</it>, <it>acs</it>, <it>actP</it> and <it>acnA</it>). Inactivation of <it>rpoS</it> had an important effect on stoichiometric parameters and growth adaptation on glycerol. The observed overexpression of <it>poxB</it>, <it>pta</it>, <it>acs</it> genes, glyoxylate shunt genes (<it>aceA, aceB</it>, <it>glcB</it> and <it>glcC</it>) and <it>actP</it>, 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 <it>poxB</it> or <it>pckA</it> 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 <it>tnaA</it> gene, no indole was detected and acetate and lactate were accumulated. A high efficiency aromatic compounds production capability was detected in JM101 carrying pJLB<it>aroG</it>^<it>fbr</it><it>tktA</it>, when growing on glycerol, as compared to glucose.</p> <p>Conclusions</p> <p>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.</p>