The Synthetic Nature of Biology

Xenobiology for the Biocontainment of Synthetic Organisms: Opportunities and Challenges

Since the development of recombinant DNA technologies, the need to establish biosafety and biosecurity measures to control genetically modified organisms has been clear. Auxotrophies, or conditional suicide switches, have been used as firewalls to avoid horizontal or vertical gene transfer, but their efficacy has important limitations. The use of xenobiological systems has been proposed as the ultimate biosafety tool to circumvent biosafety problems in genetically modified organisms. Xenobiology is a subfield of Synthetic Biology that aims to construct orthogonal biological systems based on alternative biochemistries. Establishing true orthogonality in cell-based or cell-free systems promises to improve and assure that we can progress in synthetic biology safely. Although a wide array of strategies for orthogonal genetic systems have been tested, the construction of a host harboring fully orthogonal genetic system, with all parts operating in an orchestrated, integrated, and controlled manner, still poses an extraordinary challenge for researchers. In this study, we have performed a thorough review of the current literature to present the main advances in the use of xenobiology as a strategy for biocontainment, expanding on the opportunities and challenges of this field of research.

(Re-)Designing Nature? An Overview and Outlook on the Ethical and Societal Challenges in Synthetic Biology

This structured literature analysis aims to map the current, emerging, and predicted future of synthetic biology (SB) by putting the focus on the implied conceptual, societal, and ethical challenges. The central objective of the analysis is to provide an initial systematization of the ethical and socio-scientific debate on SB by structuring and categorizing widely discussed issues within the debate in recent years. Starting with the quest for possible definitions, issues of biosafety and biosecurity are emphasized. Furthermore, the focus is on the more conceptual challenges of SB, including the relationship between natural and synthetic, or concepts of life and living. From the very beginning, one specific characteristic of SB has been a strong entanglement with different forms of public participation. In some respects SB has already taken a leading position in claiming and orchestrating itself as an integrative and participatory discipline. After addressing SB as an emerging biotechnology at the interface between science and society, a venture is initiated to focus on the possible regulatory and governmental challenges which are entangled in SB.

Creating life and the media: translations and echoes

Synthetic biology is the engineering view on biotechnology that ultimately aims at fulfilling the quest of building an artificial cell. From the very first attempts of synthesizing life, this subject has made an impact on the media through, very often, misleading headlines and news. We review here the historical journalistic approach on synthetic biology and related disciplines, from the early twentieth century to the lastest achievements on designing protocells or genome reduction. However, it would be very naive to consider the research community and the media to be unidirectionally linked, with the latter being mere displayers (and disrupters) of the research "reality". On the contrary, the research community has also received a strong influence from the media, as evidenced by statements from researchers, common metaphors and, even, a trend to unconsciously develop shared techno-social paradigms. We conclude that, beyond overstatements from researchers and journalists' misunderstandings, both communities provide strong feedback to each other and, together, contribute to define the dream that synthetic biologists are aiming for.

Xenobiology: State-of-the-Art, Ethics, and Philosophy of New-to-Nature Organisms

The basic chemical constitution of all living organisms in the context of carbon-based chemistry consists of a limited number of small molecules and polymers. Until the twenty-first century, biology was mainly an analytical science and has now reached a point where it merges with engineering science, paving the way for synthetic biology. One of the objectives of synthetic biology is to try to change the chemical compositions of living cells, that is, to create an artificial biological diversity, which in turn fosters a new sub-field of synthetic biology, xenobiology. In particular, the genetic code in living systems is based on highly standardized chemistry composed of the same "letters" or nucleotides as informational polymers (DNA, RNA) and the 20 amino acids which serve as basic building blocks for proteins. The universality of the genetic code enables not only vertical gene transfer within the same species but also horizontal gene transfer across biological taxa, which require a high degree of standardization and interconnectivity. Although some minor alterations of the standard genetic code are found in nature (e.g., proteins containing non-conical amino acids exist in nature, and some organisms use alternated coding systems), all structurally deep chemistry changes within living systems are generally lethal, making the creation of artificial biological system an extremely difficult challenge.In this context, one of the great challenges for bioscience is the development of a strategy for expanding the standard basic chemical repertoire of living cells. Attempts to alter the meaning of the genetic information stored in DNA as an informational polymer by changing the chemistry of the polymer (i.e., xeno-nucleic acids) or by changes in the genetic code have already yielded successful results. In the future this should enable the partial or full redirection of the biological information flow to generate "new" version(s) of the genetic code derived from the "old" biological world.In addition to the scientific challenges, the attempt to increase biochemical diversity also raises important ethical and philosophical issues. Although promotors of this branch of synthetic biology highlight the many potential applications to come (e.g., novel tools for diagnostics and fighting infection diseases), such developments could also bring risks affecting social, political, and other structures of nearly all societies.

Synthetic alienation of microbial organisms by using genetic code engineering: Why and how?

The main goal of synthetic biology (SB) is the creation of biodiversity applicable for biotechnological needs, while xenobiology (XB) aims to expand the framework of natural chemistries with the non-natural building blocks in living cells to accomplish artificial biodiversity. Protein and proteome engineering, which overcome limitation of the canonical amino acid repertoire of 20 (+2) prescribed by the genetic code by using non-canonic amino acids (ncAAs), is one of the main focuses of XB research. Ideally, estranging the genetic code from its current form via systematic introduction of ncAAs should enable the development of bio-containment mechanisms in synthetic cells potentially endowing them with a "genetic firewall" i.e. orthogonality which prevents genetic information transfer to natural systems. Despite rapid progress over the past two decades, it is not yet possible to completely alienate an organism that would use and maintain different genetic code associations permanently. In order to engineer robust bio-contained life forms, the chemical logic behind the amino acid repertoire establishment should be considered. Starting from recent proposal of Hartman and Smith about the genetic code establishment in the RNA world, here the authors mapped possible biotechnological invasion points for engineering of bio-contained synthetic cells equipped with non-canonical functionalities.

Erasing Borders: A Brief Chronicle of Early Synthetic Biology

Synthetic Biology is currently presented as an emergent field involving the application of engineering principles to living matter. However, the scientific pursuit of making life in a laboratory is not new and has been the ultimate, if somewhat distant, aim of the origin-of-life research program for many years. Actually, over a century ago, the idea that the synthesis of life was indispensable to fully understand its nature already appealed to material scientists and evolutionists alike. Jacques Loeb proposed a research program from an engineering standpoint, following a synthetic method (experimental abiogenesis) and based on his mechanist vision of living beings, which he considered true chemical machines. Early synthetic biology endeavors, such as the premature experiments by Alfonso L. Herrera in Mexico, Stéphane Leduc in France, and John B. Burke in United Kingdom, were easily ridiculed on both scientific and ideological grounds. However, in retrospect, all those attempts should be considered as legitimate and sincere anti-vitalistic efforts to cross the apparent border between inert and living matter.

Xenomicrobiology: a roadmap for genetic code engineering

Biology is an analytical and informational science that is becoming increasingly dependent on chemical synthesis. One example is the high‐throughput and low‐cost synthesis of DNA, which is a foundation for the research field of synthetic biology (SB). The aim of SB is to provide biotechnological solutions to health, energy and environmental issues as well as unsustainable manufacturing processes in the frame of naturally existing chemical building blocks. Xenobiology (XB) goes a step further by implementing non‐natural building blocks in living cells. In this context, genetic code engineering respectively enables the re‐design of genes/genomes and proteins/proteomes with non‐canonical nucleic (XNAs) and amino (ncAAs) acids. Besides studying information flow and evolutionary innovation in living systems, XB allows the development of new‐to‐nature therapeutic proteins/peptides, new biocatalysts for potential applications in synthetic organic chemistry and biocontainment strategies for enhanced biosafety. In this perspective, we provide a brief history and evolution of the genetic code in the context of XB. We then discuss the latest efforts and challenges ahead for engineering the genetic code with focus on substitutions and additions of ncAAs as well as standard amino acid reductions. Finally, we present a roadmap for the directed evolution of artificial microbes for emancipating rare sense codons that could be used to introduce novel building blocks. The development of such xenomicroorganisms endowed with a ‘genetic firewall’ will also allow to study and understand the relation between code evolution and horizontal gene transfer.