Synthetic Biology | Risk assessment and risk management
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5.6.2
Transfer of novel genetic material/DNA to native host organisms
Transfer of genetic material from SB organisms to native hosts may be facilitated either by vertical/sexual gene
flow or by horizontal gene transfer (HGT).
Vertical gene transfer
Modified genes may be passed on to native populations of the same or closely related species via pollen or
via
imprudent seed exchange as happened with the dispersal of transgenes among non-GM maize variants in
Mexico which has been facilitated by sloppy seed dispersal systems and grain markets (Rhodes 2010; Dyer et
al. 2009).
Horizontal gene transfer
Horizontal gene transfer between microorganisms is mediated by transformation (uptake of free DNA),
conjugation (transfer of DNA between bacteria via cell-cell contacts) and transduction (transfer of DNA
via viral
shuttles) (Lorenz and Wackernagel 1994). A major problem for assessing the risk arising from horizontal gene
transfer is the fact that comprehensive knowledge on gene transfer frequencies in natural habitats and the
involved mechanisms is still lacking (Rocha 2013). Although it is well known that horizontal gene transfer is a
hallmark in bacterial evolution bacterial gene transfer is also involved in the shaping of the evolution of
eukaryotic genomes (Rocha 2013). Concerning transformation the exchange of modified genetic material is
also possible even if the initial carrier has died (Wright et al. 2013).
Impact on biodiversity on the genetic level
Horizontal gene transfer from SB organisms to native populations may lead to a change in biodiversity at the
genetic level. A vivid example for adverse effects of HGT is the unrestricted spread of antibiotic resistance
genes in clinical and natural environments leading to a “genome pollution” of native bacterial strains with
genetic elements previously not prevalent in the exposed communities (Wright et al. 2013; International Civil
Society Working Group on Synthetic Biology (ICSWGSB) 2011). The dissemination of resistance determinants
has a profound negative impact on morbidity and mortality of patients suffering from infectious diseases and
puts a severe financial burden on public health. There is no consensus if gene transfer itself is an adverse
effect which needs to be prevented (NGOs) or only a potential mechanism by which adverse effects could
occur (EU regulatory system) (Marris and Jefferson 2013).
5.6.3
Emergence of novel properties
The application of synthetic biology techniques for the construction of new metabolic pathways
and regulatory
circuits will lead to radically different forms of life in the long run (Garfinkel and Friedman 2010; Mukunda et
al. 2009). These novel organisms may develop unpredictable new properties. It is disconcerting that the
interaction of novel circuits with endogenous pathways and the interaction with changing environmental
conditions is only rudimentary understood (Pauwels et al. 2013). There is only limited knowledge available
which allows the forward engineering of genetic devices containing a maximum of 20 genes or biological parts
at best (Schmidt and de Lorenzo 2012). Trial and error will be a long-term companion of synthetic biology and
unexpected traits will almost certainly arise (Schmidt and de Lorenzo 2012). That unforeseen results may pose
a serious health hazard is exemplified by the production of a new mouse pox virus which intentionally should
induce infertility but killed not only all of the exposed native mice but also 50% of a vaccinated - and hence
supposedly immune - control group (Schmidt and de Lorenzo 2012; Jackson et al. 2001). This observation
implies that there are clear limits of predictive knowledge (Garrett 2011). The situation will deteriorate
considering the combination of more and more elements from multiple and diverse sources of DNA (Fleming
2006).
Synthetic Biology | Discussion
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6
Discussion
This report discusses the state of the art of synthetic biology (SB), risk assessment issues, and aspects of
potential knowledge and regulatory gaps. Currently, there is still no satisfactory definition and delimitation of
the field, which results in a number of uncertainties as to which control measures need to be taken. The
recently published definition (SCENIHR et al. 2014) has deliberately been formulated in a very open way. It is
questionable whether it is adequate to allow for the clear classification of relevant activities. This is important
in particular concerning offers from companies as in this context the practice not to use the term SB was
identified.
Both genetic modification and SB are very closely interconnected, a fact that has also been acknowledged by
SCENIHR et al. (2014). Consequently, their opinion explicitly states that SB activities would currently fall under
the relevant legislation for genetically modified organisms (
i.e. Directives 2001/18/EC and 2009/41/EC, and
other relevant documents, e.g. EFSA guidance). SB organisms derived from well understood hosts and natural
sequences intended for contained use are likely to be comparable to conventional GMOs (Rodemeyer 2009).
Therefore, the current regulatory regimes on GMOs appear to sufficiently apply to near-term results of SB
techniques. On the other hand and beyond doubt there is huge potential emerging from SB. Measurability is
one of the major factors accountable for the difficulties in delimitation, as is the speed at which new concepts
emerge (SCENIHR et al. 2014). Future considerations have to take into account that in SB not all risks are
identifiable or measurable (Zhang et al. 2011). Thus, care should be taken to observe potential gaps that are
not covered by the current regulatory framework. To achieve this, monitoring of developments in the field will
be necessary, preferably on an international level. Adaption of the regulations is indicated if the complexity of
SB organisms is increasing, novel gene sequences are more profoundly modified and a greater gene pool
and/or sequence variety is used for the construction of SB microorganisms (Pauwels et al. 2013; Rodemeyer
2009).
A coordinated review of any new developments in the field of SB has to be carried out accounting for
consistency of regulatory requirements (WWICS 2014). Further, a gap analysis for
the risk assessment and data
collection of synthetic organisms may identify areas for further research. The aim of such an analysis is to
address and to compare up-to-date and outdated practices and strategies in GMO risk assessment to make
them consistent with current and future developments in SB. The purpose of the risk assessment process is to
enable to select the most suitable controls or combination of controls that are proportionate to the risk. It is
reasonable to assume that concomitant with future developments in SB many gaps are to be identified and
tackled concerning food and feed, and environmental risk assessment of synthetic organisms. These are
mainly related to limited information from practical experiences and knowledge gaps in relation to the best
experimental set-ups, and,
in general, the low data availability. It will also be necessary to determine statistical
approaches to satisfy the established requirements and safety levels. Areas of continuous refinement and
improvement are to be identified. One example is to clearly define fundamental specifications on the
requirements needed to test for any potential pathogenicity of synthetic living materials concerning tests for
carcinogenic, developmental, reproductive, hormonal, neural dysfunctions, etc. As a possible consequence,
the need to adapt current risk assessment methodologies accordingly might emerge.
Considering the capacity and potential of SB techniques it is important to be prepared for demands on new
risk assessment procedures and regulatory responses (International Civil Society Working Group on Synthetic
Biology (ICSWGSB) 2011). In particular, a debate on suitable and adequate comparators may be expected.
Current GMO risk assessment relies on the assessment of the parental organism and/or suitable conventional
comparators. This approach is inadequate for SB organisms which have no analogue in the natural world
(International Civil Society Working Group on Synthetic Biology (ICSWGSB) 2011). To be prepared for such