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Reduced evolvability of Escherichia coli MDS42, an IS-less cellular chassis for molecular and synthetic biology applications.

ABSTRACT: BACKGROUND: Evolvability is an intrinsic feature of all living cells. However, newly emerging, evolved features can be undesirable when genetic circuits, designed and fabricated by rational, synthetic biological approaches, are installed in the cell. Streamlined-genome E. coli MDS42 is free of mutation-generating IS elements, and can serve as a host with reduced evolutionary potential. RESULTS: We analyze an extreme case of toxic plasmid clone instability, and show that random host IS element hopping, causing inactivation of the toxic cloned sequences, followed by automatic selection of the fast-growing mutants, can prevent the maintenance of a clone developed for vaccine production. Analyzing the molecular details, we identify a hydrophobic protein as the toxic byproduct of the clone, and show that IS elements spontaneously landing in the cloned fragment relieve the cell from the stress by blocking transcription of the toxic gene. Bioinformatics analysis of sequence reads from early shotgun genome sequencing projects, where clone libraries were constructed and maintained in E. coli, suggests that such IS-mediated inactivation of ectopic genes inhibiting the growth of the E. coli cloning host might happen more frequently than generally anticipated, leading to genomic instability and selection of altered clones. CONCLUSIONS: Delayed genetic adaptation of clean-genome, IS-free MDS42 host improves maintenance of unstable genetic constructs, and is suggested to be beneficial in both laboratory and industrial settings.

SUBMITTER: Umenhoffer K

PROVIDER: S-EPMC2891674 | biostudies-literature | 2010

REPOSITORIES: biostudies-literature

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Reduced evolvability of Escherichia coli MDS42, an IS-less cellular chassis for molecular and synthetic biology applications.

Umenhoffer Kinga K Fehér Tamás T Balikó Gabriella G Ayaydin Ferhan F Pósfai János J Blattner Frederick R FR Pósfai György G

Microbial cell factories 20100521

<h4>Background</h4>Evolvability is an intrinsic feature of all living cells. However, newly emerging, evolved features can be undesirable when genetic circuits, designed and fabricated by rational, synthetic biological approaches, are installed in the cell. Streamlined-genome E. coli MDS42 is free of mutation-generating IS elements, and can serve as a host with reduced evolutionary potential.<h4>Results</h4>We analyze an extreme case of toxic plasmid clone instability, and show that random host ...[more]

PMID: 20492662

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Project description:BackgroundRecombinant protein production is a process of great industrial interest, with products that range from pharmaceuticals to biofuels. Since high level production of recombinant protein imposes significant stress in the host organism, several methods have been developed over the years to optimize protein production. So far, these trial-and-error techniques have proved laborious and sensitive to process parameters, while there has been no attempt to address the problem by applying Synthetic Biology principles and methods, such as integration of standardized parts in novel synthetic circuits.ResultsWe present a novel self-regulatory protein production system that couples the control of recombinant protein production with a stress-induced, negative feedback mechanism. The synthetic circuit allows the down-regulation of recombinant protein expression through a stress-induced promoter. We used E. coli as the host organism, since it is widely used in recombinant processes. Our results show that the introduction of the self-regulatory circuit increases the soluble/insoluble ratio of recombinant protein at the expense of total protein yield. To further elucidate the dynamics of the system, we developed a computational model that is in agreement with the observed experimental data, and provides insight on the interplay between protein solubility and yield.ConclusionOur work introduces the idea of a self-regulatory circuit for recombinant protein products, and paves the way for processes with reduced external control or monitoring needs. It demonstrates that the library of standard biological parts serves as a valuable resource for initial synthetic blocks that needs to be further refined to be successfully applied in practical problems of biotechnological significance. Finally, the development of a predictive model in conjunction with experimental validation facilitates a better understanding of the underlying dynamics and can be used as a guide to experimental design.

Project description:Since their discovery, archaea have not only proven a fascinating domain in their own right, but also helped us understand the evolution and function of molecular components they share with bacteria or eukaryotes. Archaeal histones are homologous to their eukaryotic counterparts, but operate in a less constrained bacterial-like cellular environment and their role in transcription and genome function remains obscure. In order to understand how archaeal histones affect transcriptional processes, we induced expression of the two histones from the archaeon Methanothermus fervidus in a naive bacterial system (E. coli) that has not evolved to integrate this kind of proteins. We show, using a series of MNase digestion experiments, that these histones bind the bacterial genome and wrap DNA in vivo in a pattern consistent with a previously proposed multimerisation model, in a similar pattern observed natively. We correlate genome-wide occupancy maps and gene expression profiles in different phases of growth to show that – although expression of archaeal histones triggers morphological changes in E. coli – there appears to only be an indirect effect on transcription. Since their discovery, archaea have not only proven a fascinating domain in their own right, but also helped us understand the evolution and function of molecular components they share with bacteria or eukaryotes. Archaeal histones are homologous to their eukaryotic counterparts, but operate in a less constrained bacterial-like cellular environment and their role in transcription and genome function remains obscure. In order to understand how archaeal histones affect transcriptional processes, we induced expression of the two histones from the archaeon Methanothermus fervidus in a naive bacterial system (E. coli) that has not evolved to integrate this kind of proteins. We show, using a series of MNase digestion experiments, that these histones bind the bacterial genome and wrap DNA in vivo in a pattern consistent with a previously proposed multimerisation model, in a similar pattern observed natively. We correlate genome-wide occupancy maps and gene expression profiles in different phases of growth to show that – although expression of archaeal histones triggers morphological changes in E. coli – there appears to only be an indirect effect on transcription.

Project description:Aim. The nascent field of bio-geoengineering stands to benefit from synthetic biologists' efforts to standardise, and in so doing democratise, biomolecular research methods. Roseobacter clade bacteria comprise 15-20% of oceanic bacterio-plankton communities, making them a prime candidate for establishment of synthetic biology chassis for bio-geoengineering activities such as bioremediation of oceanic waste plastic. Developments such as the increasing affordability of DNA synthesis and laboratory automation continue to foster the establishment of a global 'do-it-yourself' research community alongside the more traditional arenas of academe and industry. As a collaborative group of citizen, student and professional scientists we sought to test the following hypotheses: (i) that an incubator capable of cultivating bacterial cells can be constructed entirely from non-laboratory items, (ii) that marine bacteria from the Roseobacter clade can be established as a genetically tractable synthetic biology chassis using plasmids conforming to the BioBrick(TM) standard and finally, (iii) that identifying and subcloning genes from a Roseobacter clade species can readily by achieved by citizen scientists using open source cloning and bioinformatic tools. Method. We cultivated three Roseobacter species, Roseobacter denitrificans, Oceanobulbus indolifexand Dinoroseobacter shibae. For each species we measured chloramphenicol sensitivity, viability over 11 weeks of glycerol-based cryopreservation and tested the effectiveness of a series of electroporation and heat shock protocols for transformation using a variety of plasmid types. We also attempted construction of an incubator-shaker device using only publicly available components. Finally, a subgroup comprising citizen scientists designed and attempted a procedure for isolating the cold resistance anf1 gene from Oceanobulbus indolifexcells and subcloning it into a BioBrick(TM) formatted plasmid. Results. All species were stable over 11 weeks of glycerol cryopreservation, sensitive to 17 µg/mL chloramphenicol and resistant to transformation using the conditions and plasmids tested. An incubator-shaker device, 'UCLHack-12' was assembled and used to cultivate sufficient quantity of Oceanobulbus indolifexcells to enable isolation of the anf1 gene and its subcloning into a plasmid to generate the BioBrick(TM) BBa_K729016. Conclusion.The process of 'de-skilling' biomolecular techniques, particularly for relatively under-investigated organisms, is still on-going. However, our successful cell growth and DNA manipulation experiments serve to indicate the types of capabilities that are now available to citizen scientists. Science democratised in this way can make a positive contribution to the debate around the use of bio-geoengineering to address oceanic pollution or climate change.

Dataset Information

Reduced evolvability of Escherichia coli MDS42, an IS-less cellular chassis for molecular and synthetic biology applications.

Publications

Reduced evolvability of Escherichia coli MDS42, an IS-less cellular chassis for molecular and synthetic biology applications.

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