RNAseq of the the Growth Modulon of Corynebacterium glutamicum under Glucose Limited Chemostat Conditions
ABSTRACT: RNAseq of coding RNA via Illumina TruSeq stranded mRNA sequencing of C. glutamicum ATCC 13032 growing under glucose limited chemostat conditions with growth rate = 0.2, 0.3, and 0.4 h-1 in three biological replicates on Illumina HiSeq1500 platform.
Project description:To investigate the adaptation of Corynebacterium glutamicum to altering oxygen availabilities, we conceived a triple-phase fermentation process that describes a gradual reduction of dissolved oxygen depicting a shift from aerobiosis via microaerobiosis to anaerobiosis. The distinct process phases were clearly bordered by the bacteria’s physiologic response such as reduced growth rate, biomass substrate yield and altered yield of fermentation products. During the process, sequential samples were drawn at six points and analyzed via RNA-sequencing of Illumina TruSeq Stranded mRNA libaries sequenced paired end on an Illumina MiSeq system using 75 nt read length. We found transcriptional alterations of almost 50 % (1421 genes) of the entire protein coding genes and observed an upregulation of fermentative pathways, a rearrangement of respiration and mitigation of the basic cellular mechanisms such as transcription, translation and replication as a transient response related to the installed oxygen dependent process phases.
Project description:We aimed to study how production of p-coumaric acid, a precursor of multiple secondary aromatic metabolites, influences the cellular metabolism of Saccharomyces cerevisiae. We evaluated the growth and p-coumaric acid production in batch and chemostat cultivations and analyzed the transcriptome and intracellular metabolome during steady state in low- and high-producers of p-coumaric acid in two strain backgrounds, S288c or CEN.PK. For analysis of the differential gene expression, we did pairwise comparisons between the optimized and non-optimized strains for p-CA production: CEN.PK strains (ST4288 and ST4408) and the S288c strains (ST4353 and ST4397). Transcriptome analysis showed that the CEN.PK strain was less affected by engineering towards higher p-CA production than the S288c strain, as the number of significantly up-/down-regulated genes was correspondingly 652 and 1927 amongst others, strain S288c had downregulations in gene sets involved in amino acid and protein biosynthesis. This suggests that CEN.PK may be a better platform strain for production of aromatic compounds than the S288c strain.
Project description:The growth rate (µ) of microbes is a fundamental property influencing its production capacity. To identify the transcriptomic changes of Corynebacterium glutamicum ATCC13032 with increasing growth rate, three transitions, induced by different pre-culture conditions, were sampled in triplicate at growth rates ranging from 0.02 to 0.4 h-1. The pre-culture conditions differed in limiting substrate (phosphate, nitrogen, carbon) and the length of the stationary phase. Samples of 2 mL were withdrawn from the bioreactor in biological triplicates and immediately centrifuged at 20000 g for 30 seconds at 4 °C. The supernatant was discarded and the remaining cell pellet was immediately flash frozen in liquid nitrogen. Total RNA was isolated from three biological replicates using RNeasy Mini Kit along with a DNase Kit (both from Qiagen). Initially RNA quality was checked by Trinean Xpose (Gentbrugge,Belgium) and Agilent RNA Nano 6000 kit on Agilent 2100 Bioanalyzer (Agilent Technologies, Böblingen, Germany). Samples contaminated with DNA were treated with DNase (Qiagen), cleaned as described above and rechecked by Xpose and Agilent Bioanalyzer. Finally RNA was free of DNA with an RNA Integrity Number (RIN) > 9 and rRNA Ratio [23s / 16s] > 1.5. Ribo-Zero rRNA Removal Kit (Bacteria) from Illumina (San Diego, CA, USA) was used to remove the ribosomal RNA molecules from the isolated total RNA. Removal of rRNA was checked by Agilent RNA Pico 6000 kit on Agilent 2100 Bioanalyzer (Agilent Technologies, Böblingen, Germany). RNA was free of detectable rRNA. TruSeq Stranded mRNA Library Prep Kit from Illumina (San Diego, CA, USA) was used to prepare cDNA libraries. The resulting cDNAs were sequenced paired end on an Illumina MiSeq system using 75 bp read length and on Illumina HiSeq 1500 system using 70 bp read length and 50 bp read length for one single sample. Through the comparison of these three datasets, each containing three biological replicates, the pre-condition independent gene expression changes could be deduced and the growth rate modulon was identified.
Project description:Nitrogen limitation is a major regulator to initiate lipid overproduction in oleaginous fungi. To examine the influence of nitrogen starvation, chemiostat cultures of R. toruloides in defined media with abundant ammonium (MM) or minute ammonium (MM-N) were performed to obtain steady-state samples. Then Illumina's digital gene expression (DGE) technology was used for high-throughput transcriptome profiling of these samples. Two samples cultured in minimum media with abundant ammonium (MM) or minute ammonium (MM-N)
Project description:Saccharomyces cerevisiae is an established microbial host for the production of non-native compounds. The synthesis of these compounds typically demands energy and competes with growth for carbon and energy substrate. Uncoupling product formation form growth would benefit product yields and decrease formation of by-product biomass. Studying non-growing metabolically-active yeast cultures provides a first step towards developing S. cerevisiae as a non-growing, robust cell factory. Non-growing metabolically-active cultures can be obtained in retentostat, a glucose-limited, continuous bioreactor system in which biomass accumulates while spent medium is constantly removed. Hitherto retentostat cultures of S. cerevisiae have only been reported under anaerobiosis, condition inappropriate for the production of energy-demanding products. The present study, using retentostat cultures, explores the physiology of non-dividing, fully respiring S. cerevisiae, focusing on industrially-relevant features. Following model-aided experimental design, retentostat cultivations were optimized for accelerated but smooth transition of S. cerevisiae from exponential growth to near-zero growth rates. During 20 days in retentostat the biomass concentration increased, leading very slow growth rates (specific growth rates below 0.001 h-1) but high culture viability (over 80% of viable cells). The maintenance requirement (mATP) was estimated at 0.64 mmolATP.gX-1.h-1, which is remarkably ca. 35% lower than the mATP measured in anaerobic retentostat cultures. Transcriptional down-regulation of genes involved in biosynthesis and up-regulation of stress-responsive genes towards near-zero growth rates corresponded well with data from anaerobic retentostats. More striking was the extreme heat-shock tolerance of S. cerevisiae, which exceeded by far previously reported heat shock tolerance of notoriously robust yeast cultures such as stationary phase cultures. Furthermore, while the metabolic fluxes in the retentostats were relatively low as a result of extreme caloric restriction, off-line measurements revealed that S. cerevisiae retained a high catabolic capacity. The high viability and extreme heat-shock tolerance revealed the robustness of S. cerevisiae at near-zero growth in retentostat. In addition, the relatively low maintenance requirements and high metabolic capacity under severe calorie restriction underline the potential of S. cerevisiae as a non-dividing microbial cell factory for the production of energy-intensive compounds. The retentostat is a promising tool to identify the molecular basis of this extreme robustness. The goal of the present study is to investigate the physiology of aerobic fully respiring S. cerevsiae at near-zero growth rates. Fundamental but industrially-relevant questions were addressed thanks to the design, implementation and study of aerobic retentostat cultivations enabling a rapid but smooth transition of S. cerevisiae from exponential growth to near-zero growth rates.
Project description:Development of microtiter plate based microbioreactor cultivation for Aspergillus giganteus with quasi-continuous online measurements. Different parameters such as well geometry, shaking frequency and morphology controlling agents were investigated in order to optimize the microtiter plate cultivation and scattered light signal towards reproducibility and homogeneity. An optimized medium was developed and scalability into stirred tank bioreactor cultivation was analyzed. As a transferability indicator the supernatant of both cultivation systems was analyzed for secreted protein patterns with a focus on an antifungal protein (AFP) and alpha-sarcin. These proteins were identified via LC-MS/MS.
Project description:Corynebacterium glutamicum is well-known as an industrial workhorse, most notably for its use in the bulk production of amino acids in the feed and food sector. Fast growth and robustness against oscillatory oxygen availability, which can occur in large-scale bioreactors, are advantageous properties of this bacterium. However, previous studies of the effect of gradients in scale-down reactors with complex media disclosed an accumulation of several carboxylic acids and a parallel decrease of growth and product accumulation by C. glutamicum. This study addresses the impact of carboxylic acids, e.g. acetate and L-lactate, on the cultivation process and their potential role in scale up related performance losses. In order to mimic a discontinuous oxygen supply, a fluctuating power input in shake flask and stirred tank cultivations with mineral salt was applied. One focus of this study is to identify relative changes in the proteome due to the differing availability of carboxylic acids under discontinuous oxygen supply.
Project description:Clostridium thermocellum is a promising CBP candidate organism capable of directly converting lignocellulosic biomass to ethanol. Low yields, productivities and growth inhibition prevent industrial deployment of this organism for commodity fuel production. Symptoms of potential redox imbalance such as incomplete substrate utilization, and fermentation products characteristic of overflow metabolism, have been observed during growth. This perceived redox imbalance may be in part responsible for the mentioned bioproductivity limitations. Toward better understanding the redox metabolism of C. thermocellum, we analyzed gene expression, using microarrays, during addition of two stress chemicals (methyl viologen and hydrogen peroxide) which we observed to change fermentation redox potential. High quality RNA was extracted from C. thermocellum grown on cellobiose in chemostat culture and exposed, separately, to methyl viologen and hydrogen peroxide. Transcriptome profiles were obtained at seven time points during actively growing fermentations, 3 minutes, 15 minutes, 35 minutes, 7 hours, 14 hours, 50 hours, and 60 hours after beginning exposure to each stressor. Exposure treatments were carried out in duplicate and reference/untreated samples were taken before and between treatments, after flushing of stressor chemicals and re-equilibration of growth conditions.
Project description:Pichia pastoris is a widely used yeast platform for heterologous protein production. Although increasing gene dosage is a powerful strategy to improve recombinant protein production, an excess in the number of gene copies often leads to decreased product yields and increased metabolic burden. In order to find the bottlenecks of this strategy, here we present a transcriptome profile comparison of a series of Pichia pastoris strains carrying a different gene dosage of the Rhizopus oryzae lipase (Rol) as a model protein. Cells were grown on a mixture of glycerol:methanol in chemostat cultures. 2 color experiment in reference design.
Project description:This work presents an exploration of submerged differentiation of the ubiquitous saprophyte and industrially important fungus, Aspergillus niger, in response to a limited availability of a sole carbon and energy source, maltose. In aspergilli and other mold fungi, asexual reproduction through formation of elaborate conidiogenic structures normally requires an aerial interface. This requirement is bypassed in submerged culture in response to severe nutrient limitation. Continuous cultures with cell retention (retentostat cultures) were applied to generate a fundamental physiological state, where the specific growth rate approaches zero, as the density of the cell population adapts to the supply of the limiting energy source. Temporal differentiation of mycelium structure and commitment to asexual reproduction were major phenomena, apparent on biochemical, morphological, physiological, and transcriptomic level. The severe substrate limitation had a rapid negative impact on cytoplasmic processes, and promoted endo- and exogenous nutrient mobilization, and hyphal compartmentalisation. The first conidiogenic structures appeared after one day with little additional differentiation until Day 4 to 6, where a transition to full commitment to reproductive growth took place. Submerged conidiation in A. niger involved transcriptional regulation of homologs of the regulatory pathway, centered around the Bristle gene (brlA), and structural genes previously described in other aspergilli. Comparison of transcriptomes, revealed a number of co-regulated gene clusters, which appear to encode secondary metabolite biosynthetic potential. We discuss the concept of maintenance energy in the context of differentiation, a possible physiological trigger for sporulation and the special physiological adaptations of the starved mycelium. We also present a simple and efficient method for in situ retention of filamentous organisms. The dataset consists of 9 Affymetrix arrays derived from defined growth conditions of lab-scale bioreactor cultures (5L). Total RNA was extracted from biomass harvested at three different growth phases: exponential growth phase, 2 and 8 days of retentostat cultivation. For each of the phases, the data is derived from three biological replicates.