Project description:Microbes able to convert gaseous one-carbon (C1) waste feedstocks are increasingly important to transition to the sustainable production of renewable chemicals and fuels. Acetogens are interesting biocatalysts since gas fermentation using Clostridium autoethanogenum has been commercialised. However, most acetogen strains need complex nutrients, display slow growth, and are not robust for bioreactor fermentations. In this work, we used three different and independent adaptive laboratory evolution (ALE) strategies to evolve the wild-type C. autoethanogenum to grow faster, without yeast extract and to be robust in operating continuous bioreactor cultures. Multiple evolved strains with improved phenotypes were isolated on minimal media with one strain, named “LAbrini”, exhibiting superior performance regarding the maximum specific growth rate, product profile, and robustness in continuous cultures. Whole-genome sequencing of the evolved strains identified 25 mutations. Of particular interest are two genes that acquired seven different mutations across the three ALE strategies, potentially as a result of convergent evolution. Reverse genetic engineering of mutations in potentially sporulation-related genes CLAU_3129 (spo0A) and CLAU_1957 recovered all three superior features of our ALE strains through triggering significant proteomic rearrangements. This work provides a robust C. autoethanogenum strain “LAbrini” to accelerate phenotyping and genetic engineering and to better understand acetogen metabolism.
Project description:Microbes able to convert gaseous one-carbon (C1) waste feedstocks are increasingly important to transition to the sustainable production of renewable chemicals and fuels. Acetogens are interesting biocatalysts since gas fermentation using Clostridium autoethanogenum has been commercialised. However, most acetogen strains need complex nutrients, display slow growth, and are not robust for bioreactor fermentations. In this work, we used three different and independent adaptive laboratory evolution (ALE) strategies to evolve the wild-type C. autoethanogenum to grow faster, without yeast extract and to be robust in operating continuous bioreactor cultures. Multiple evolved strains with improved phenotypes were isolated on minimal media with one strain, named “LAbrini”, exhibiting superior performance regarding the maximum specific growth rate, product profile, and robustness in continuous cultures. Whole-genome sequencing of the evolved strains identified 25 mutations. Of particular interest are two genes that acquired seven different mutations across the three ALE strategies, potentially as a result of convergent evolution. Reverse genetic engineering of mutations in potentially sporulation-related genes CLAU_3129 (spo0A) and CLAU_1957 recovered all three superior features of our ALE strains through triggering significant proteomic rearrangements. This work provides a robust C. autoethanogenum strain “LAbrini” to accelerate phenotyping and genetic engineering and to better understand acetogen metabolism.
Project description:These E. coli strains were grown with various signaling molecules and the expression profiles were determined. Keywords: addition of quorum and host hormone signals
Project description:Escherichia coli BW25113 is the parent strain of the Keio collection comprising nearly 4,000 single-gene deletion mutants. We report the complete 4,631,469-bp genome sequence of this strain and the key variations from the type strain E. coli MG1655.
Project description:We obtained pfkAB-deleted E. coli K-12 MG1655 strain that can thrive on glucose minimal medium with adaptive laboratory evolution (pfk_ALE-1 strain). Functional analysis of the mutations detected in the pfk_ALE-1 strain was conducted to elucidate the molecular mechanisms underlying the effects of these mutations. We performed transcriptome analysis with RNA-seq to investigate the transcriptomic effects of mutations involved in the glycolytic pathway and global transcriptional regulation. Transcriptomic analysis revealed the expression levels of 4,497 genes on the chromosome of MG1655 and ALE-1 strains.
Project description:Laboratory adaptive evolution experiments were conducted using serial passage of E. coli in M9 minimal medium supplemented with either 2 g/L of lactate for 60 days or 2 g/L of glycerol for 44 days. 7 parallel evolution strains were generated for growth on lactate and 7 parallel evolution strains were generated for growth on glycerol. Affymetrix arrays were used to study the time-course change in gene expression from unevolved E. coli (day 0) to a midpoint evolved strain (day 20) and evolutionary endpoints
Project description:One of the key issues affecting yields of biovanillin in cell factories such as Escherichia coli is product toxicity, the mechanisms of which are poorly understood. To identify targets for engineering improved strains, we have studied mechanisms of vanillin toxicity in E. coli using a two-pronged apparoach: (i) a global proteomic analysis supported by multiple physiological experiments and mutant analyses (ii) adaptive laboratory evolution (ALE) of vanillin tolerance combined with genome sequencing. We identified 147 proteins that exhibited a significant change in abundance in response to vanillin. Upregulated proteins included enzymes capable of converting aldehydes to potentially less toxic compounds; pentose phosphate pathways enzymes, fumarase C and enzymes of the glyoxylate shunt; proteins involved in several key stress responses, in particular oxidative stress; proteins mediating uptake and processing of metal ions. 1H-NMR confirmed that E. coli detoxifies vanillin by reduction to vanillyl alcohol; the aldehyde reductases YqhD and DkgA were highly upregulated by vanillin and the purified enzymes reduced vanillinin an NADPH dependent manner. Vanillin caused accumulation of reactive oxygen species and activated an oxidative stress response through SoxRS, OxyR and MarA pathways. Slow vanillin dependent copper (II) to copper (I) reduction lead to upregulation of the copA gene and growth in the presence of vanillin was hypersensitive to inhibition by copper ions. RT-PCR and mutant growth data suggested AcrD and AaeAB as potential vanillin efflux systems. Vanillin-tolerant strains isolated by ALE had distinct non-synonymous SNPs in the citrate synthase gene gltA, in addition to strain specific mutations in cpdA, rob and marC. One strain had a large ~10 kb deletion including the marRAB region. Purifed variant GltA enzymes all showed higher activity due to a lowered Km for oxaloacetate. Our data provide new understanding and novel gene targets for engineering vanillin-tolerant strains of E. coli, including deletion of the efflux pumps eamA, acrA, and acrB, enhancing oxidative stress defences and NADPH production, improving copper homeostasis and increasing citrate synthase activity using variant enzymes.
Project description:Using a synthetic biosensor to couple production of a specific metabolite with cell growth, we spontaneously evolved cells under the selective condition toward the acquisition of genotypes that optimally reallocated cellular resources. Using 3-hydroxypropionic acid (3-HP) production from glycerol in Escherichia coli as a model system, we determined that spontaneous mutations in the conserved regions of proteins involved in global transcriptional regulation altered the expression of several genes associated with central carbon metabolism. Our study provides a new perspective on adaptive laboratory evolution (ALE) using synthetic biosensors, thereby supporting future efforts in metabolic pathway optimization.
Project description:In order to understand the impact of genetic variants on transcription and ultimately in changes in observed phenotypes we have measured transcript levels in an Escherichia coli strains collection, for which genetic and phenotypic data has also been measured.