Utilization of γ-Aminobutyric Acid as the Sole Carbon and Nitrogen Source by Escherichia coli K-12 Mutants

Zhang

et al. 2006

Molecular Microbiology

SummaryQuorum sensing (QS) signal decay in Agrobacterium tumefaciens occurs in response to starvation or host signals. We have demonstrated that the g-aminobutyric acid (GABA) shunt metabolite links stress response to QS signal decay. Mutation of the aldH gene encoding a succinic semialdehyde dehydrogenase (SSADH) that converts succinic semialdehyde (SSA) to succinic acid results in early expression of the signal degrading enzyme, AttM. Exogenous addition of SSA or its precursor GABA induces AttM expression and abolishes Ti plasmid conjugative transfer. SSA acts by binding to the repressor AttJ that regulates the attKLM operon. attK encodes another SSADH. The stress alarmone ppGpp and SSA modulates separately the expression of the two SSADH enzymes, which might control the intracellular SSA level and hence to switch on/off the QS signal decay system in response to environmental changes. These findings document for the first time a sophisticated signalling mechanism of the widely conserved GABA degradation pathway in prokaryotes.

Section: Discussionmentioning

confidence: 75%

Succinic semialdehyde couples stress response to quorum‐sensing signal decay in Agrobacterium tumefaciens

Zhang

et al. 2006

Molecular Microbiology

Plant Cell & Environment

“…It has been reported that GABA could be utilized to the sole nitrogen source in the growth of Escherichia coli (Dover & Halpern 1972) polyamine (b) production in Caragana intermedia roots. The seedlings were treated with 300 mm NaCl and 300 mm NaCl + 10 mm GABA for the designated times.…”

Section: Is Gaba a Signal Molecule Or Nitrogen Source?mentioning

confidence: 99%

Effects of exogenous GABA on gene expression of Caragana intermedia roots under NaCl stress: regulatory roles for H₂O₂ and ethylene production

Shi

Jiang

et al. 2010

170

117

ABSTRACTg-aminobutyric acid (GABA) is a four-carbon non-protein amino acid presented in a wide range of organisms. In this study, a suppression subtractive hybridization (SSH) library was constructed using roots of a legume shrub, Caragana intermedia, with the combined treatment of 300 mM NaCl and 300 mM NaCl + 10 mM GABA. We obtained 224 GABA-regulated unique expressed sequence tags (ESTs) including signal transduction, transcriptional regulation, hormone biosynthesis, reactive oxygen species (ROS) and polyamine metabolism, etc. The key H2O2-generated genes, NADPH oxidase (CaGR60), peroxidase (CaGR61) and amine oxidase (CaGR62), were regulated at the mRNA level by 10 mM GABA, which clearly inhibited H2O2 accumulation brought about by NaCl stress in roots and leaves with the observation of 3,3Ј-diaminobenzidine (DAB) staining. Similarly, 10 mM GABA also regulated the expression of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) genes (CaGR30 and CaGR31) and ethylene production in NaCl-treated roots. Surprisingly, these H2O2-generated genes were enhanced at the mRNA level by a lower concentration of GABA, at 0.25 mM, but not other alternative nitrogen sources, and endogenous GABA accumulated largely just by the application of GABA at either concentration. Our results further proved that GABA, as a signal molecule, participates in regulating the expression of genes in plants under salt stress.

“…Recombinant E. coli strains were grown in LB medium. When GABA or glutamate was provided as supplemental carbon source, 0.1 M dimethylsulfoxide was added to facilitate uptake of these substrates (Dover and Halpern, 1972). Cultures were incubated at 30°C and shaken at 225 rpm until an OD 600 of 0.6 was reached.…”

Section: Pha Accumulation Experimentsmentioning

confidence: 99%

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) formation from γ-aminobutyrate and glutamate

Valentin

Reiser

Gruys

2000

Biotechnol. Bioeng.

To provide 4-hydroxybutyryl-CoA for poly(3-hydroxybutyrate-co-4-hydroxybutyrate) formation from glutamate in Escherichia coli, an acetyl-CoA:4-hydroxybutyrate CoA transferase from Clostridium kluyveri, a 4-hydroxybutyrate dehydrogenase from Ralstonia eutropha, a gamma-aminobutyrate:2-ketoglutarate transaminase from Escherichia coli, and glutamate decarboxylases from Arabidopsis thaliana or E. coli were cloned and functionality tested by expression of single genes in E. coli to verify enzymatic activity, and uniquely assembled as operons under the control of the lac promoter. These operons were independently transformed into E. coli CT101 harboring the runaway replication vector pJM9238 for polyhydroxyalkanoate (PHA) production. Plasmid pJM9238 contains the PHA biosynthetic operon of R. eutropha under tac promoter control. Polyhydroxyalkanoate formation was monitored by nuclear magnetic resonance (NMR) spectroscopic analysis of the chloroform extracted and ethanol precipitated polyesters. Functionality of the biosynthetic pathway for copolymer production was demonstrated through feeding experiments using various carbon sources that supplied different precursors within the 4HB-CoA biosynthetic pathway.