Environmental performance and containment

While knowledge of the biology and environmental behaviour, including pathogenicity, of a GMM is of crucial importance in a risk assessment, the recombinant genes also need to be assessed, since they may dramatically change the potential of an organism to survive outside of the laboratory. However, increasing the capacity of a GMM to survive in the environment is not a risk per se, as it may be an intended effect of the modification, e.g. to persist in a contaminated soil and degrade organic pollutants. Results with current bacterial inoculants, in fact, indicate that the risk of failure of a GMM to perform its desired activity in such soils is much higher than the risk it would impose on natural microbial communities (de Lorenzo, 2009). Similar constraints are likely to limit the success of bacterial inoculants in agriculture, e.g. to replace chemical fertilisation by biological nitrogen-fixation or phosphate mobilisation. A potential approach to enhance the viability and desired biological activities of bacterial inoculants could be to alter the expression of their natural genes by engineering their own promoters (Ryan et al., 2009). The huge gain of knowledge due to high throughput DNA-sequencing and bioinformatics delivers the tools which will probably allow progress from “spray and prey” to the successful design of GMM for more effective and reliable environmental applications (de Lorenzo, 2008). Should their survival and environmental exposure be enhanced through these practices, then the environmental risk assessment could differ in its level of required scrutiny from those applied before.

Ideally, GMM, once they have finished the job (for which they were designed), should disappear from the environment. A number of such concepts for containment, including bacteria with decreased fitness to repair mutations or substrate-inducible suicide-systems, have been developed and tested in the field and this principle of biological containment may become important for future applications (Molin et al., 1993; Schwieger et al., 2000; Torres et al., 2000). Due to the potential for mutational changes or other factors, such containment systems may not be 100% secure. On the other hand, bacterial symbionts, i.e. Wolbachia appear to be highly efficient containments systems, suggesting that for the control of insect-borne diseases the environmental spread of a GMM would be negligible (Alphey et al., 2002; Moreira et al., 2009).

An unintended environmental persistence of a GMM does not immediately and necessarily present a risk, since micro-organisms may be in resting cell stages, thus, metabolically inactive outside of their natural niche, or their metabolic activity may not interfere with the ecosystem functions provided by the existing microbial communities (see above the example of S. meliloti). The environmental persistence of a GMM may, however, correlate with its potential to travel beyond the immediate areas of application and thus enter non-target environments and ecosystems, which consequently would require an extended risk assessment of non-target effects. In this respect, GMMs with a tight symbiotic relationship, i.e. Wolbachia with insects or S. meliloti with certain legumes, could be preferable species for environmental applications.

 
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