The language of Physics and Engineering is precise and unequivocal. If we say Ampere, vector, gravity or the thread angle of a screw thread we know exactly what the terms mean. In contrast, the jargon of Synthetic Biology, which inter alia aims to bring Biology to the realm of engineering seems to be peppered with words and metaphors which are in reality more a declaration of intentions (or wishes) than an accurate description of the thereby named items. One of the central notions of contemporary SynBio is that of chassis, a term that evokes the basic frame of a car in which a number of components can be added in response to specifications and/or customers’ desires. By the same token, the term started to be used in the 2000 by the incipient SynBio community of the time as a humorous and engineering-sounding description of the biological host used as the recipient of recombinant DNA—which by that time meant nearly exclusively E. coli.
The word chassis (and its powerful metaphor embodied in it) became an instant success and it was quickly incorporated to the habitual discourse of SynBio-as-engineering. But at the same time, the word has acquired new meanings over the years and has been used in many different SynBio contexts beyond its original and somewhat modest significance. The prevailing meaning is that of a more or less improved host for genetic constructs whether in bacteria yeast, fungi, archaea, animal or plant cells. But the name has also been applied to organisms with edited genomes for enhancing this or that trait of interest as well as bacteria with minimized DNA contents, including altogether synthetic genomes. Moreover, cell-free systems, reconstructed vesicles and nucleoid-dissolved cells (i.e. with no DNA) have also been described as chassis. In a further move, subsets of biochemical reactions either implemented in vitro or simulated in silico are also often referred to as chassis. The word has thus quickly undergone a process of liberal trans-signification to the point that the metaphor is kept in all cases but the precise meaning has become growingly blurry. This has not been an issue thus far, but the new scenarios that SynBio starts to penetrate demand a clarification and even a definition of the term that end-users can understand without any ambiguity.
One of our key missions in the Bioroboost Project is to precisely clarify the terminology and the criteria regarding chassis in view of [i] the avalanche of new species and strains that claim recognition as SynBio platforms, [ii] the fuzzy line between organisms that are just good at receiving and maintaining recombinant DNA (ie host-vector systems) and those specifically named as SynBio chassis and [iii] the demands by regulatory bodies regarding their potential use in industry and the environment.
Text by: Víctor de Lorenzo (CNB-CSIC), October 2019