Building-in biosafety for synthetic biology

As the field of synthetic biology develops, real-world applications are moving from the realms of ideas and laboratory-confined research towards implementation. A pressing concern, particularly with microbial systems, is that self-replicating re-engineered cells may produce undesired consequences if they escape or overwhelm their intended environment. To address this biosafety issue, multiple mechanisms for constraining microbial replication and horizontal gene transfer have been proposed. These include the use of host-construct dependencies such as toxin-antitoxin pairs, conditional plasmid replication or the requirement for a specific metabolite to be present for cellular function. While refactoring of the existing genetic code or tailoring of orthogonal systems, e.g. xeno nucleic acids, offers future promise of more stringent 'firewalls' between natural and synthetic cells, here we focus on what can be achieved using existing technology. The state-of-the-art in designing for biosafety is summarized and general recommendations are made (e.g. short environmental retention times) for current synthetic biology projects to better isolate themselves against potentially negative impacts.