Overview of potential risks of GM-algae for human health and the environment

The European Commission has developed guidance notes for risk assessment of the use of GMOs. Guidance Note 2000/608/EC (European Union, 2000) deals with risk assessment of contained use of genetically modified micro-organisms while Guidance Note 2002/623/EC (European Union, 2002) deals with the risk assessment of deliberate release into the environment of genetically modified organisms. This section discusses elements of the risk analysis methodology as developed in these guidance notes.

Safety of the algae, the insert, vector and the GM-algae

With respect to contained use, the risk assessment is aimed at identifying harmful properties of the algae due to the combined characteristics of the recipient organism, the insert, the vector and the resulting GM-algae with respect to human health and the environment.

There are only a few species of algae that are classified as pathogens in humans or animals. These algae belong to the Prototheca or Chaetoceros or are mentioned on the IOC-UNESCO list of harmful algae. However, quite a number of algal species, especially belonging to the dinoflagellates and the diatoms, produce toxins that impact humans, animals and birds. In addition, some cyanobacteria also produce toxins that are harmful to humans and animals. For example, some genera that are industrially relevant contain species that are known to produce toxins, e.g. Phormidium (some strains do not produce toxins), Anabaena circinalis, A. flos-aquae, while Synechococcus wickerhami and Prototheca cutis are human or animal pathogens.

In the examples of GM-algae mentioned above, the DNA inserted in the recipient algae has been characterised. Although it is unlikely that GM-algae intended for use in outdoor cultivation systems contain inserts that have not been characterised, a differentiation between donor organisms in terms of toxin producer, pathogens or non-toxin producer non-pathogen will influence the risk assessment when uncharacterised genes have been used to produce the GM-algae, as uncharacterised genes may be involved in toxin production or pathogenicity.

When looking at the targets of genetic modification of algae, the following groups of genes used as inserts, can be distinguished:

  • • genes involved in photosynthesis
  • • genes involved in carotenoid biosynthesis
  • • genes involved in lipid biosynthesis
  • • genes encoding (pharmaceutical) proteins
  • • regulatory genes such as transcription factors or other metabolic regulators.

In general, the genetic modification of algae aimed at modifying either photosynthesis, carotenoid biosynthesis or lipid biosynthesis is not expected to generate harmful strains with respect to human health. None of the genes used encode for toxins or are suspected to lead to toxin production through enhanced metabolic steps or metabolic pathways, especially when they are expressed in “safe” algae hosts.

However, introducing genes in the host may have phenotypic effects and for that reason it is argued that these effects should be analysed. When expressing pharmaceutical proteins (e.g. antibodies), the potential effects of these proteins on humans have to be addressed in the risk assessment.

In eukaryotic algae, the donor DNA is integrated in the genomic or chloroplast DNA. Only Chlamydomonas reinhardtii has a history of stable genetic modifications and subsequent cultivation of the GM-strains. Stability of other GM-algae (which is mainly an issue in the production using these algae) still has to be confirmed, especially under non-selective conditions since stability will most likely be gene and integration dependent. As cyanobacteria are bacteria, vector DNA can be integrated into the genome, but vectors, which can replicate in the cytoplasm, are also used. The methodology of risk assessment used for GMOs can be applied to cyanobacteria without major modifications.

Transfer of genetic material to other organisms

An important aspect to be addressed in the ERA is the transfer of inserted genetic material to other organisms. Therefore, horizontal gene transfer (HGT) - the transfer of genetic material from one organism to another which is a natural mechanism and has played an important role in evolution - is a point of concern.

In cyanobacteria, where ~50% of extended gene families putatively have a history of HGT (either between cyanobacteria and other phyla, or within cyanobacteria, or both), HGT has played an important role in evolution (Zhaxybayeva et al., 2006; Monier et al., 2009). In these bacteria, HGT is a mechanism in real-time adaptation and for that reason it is part of the risk assessment of GM-bacteria.

In eukaryotic algae, HGT has been part of the evolutionary development; however, in these organisms, this is not a real-time event and poses no additional risk in GMOs.3

Vertical gene transfer uses reproduction as a means of gene transfer through generations and may be a risk with GM-algae when the species used has a sexual reproduction cycle and wild-type partners are present in the environment.

The transfer of antibiotic resistance or herbicide resistance is an issue in the debate on the safety of GMOs. Several governments in the European Union have recommended the phasing out of GM-crops containing any antibiotic resistance markers (European Federation of Biotechnology, 2001). Therefore, the use of GM-algae, without antibiotic resistance genes, for outdoor cultivation will almost certainly be more easily accepted by the public. However, as discussed above, in most of the genetic modification protocols for algae, antibiotic resistance is being used as the selection criterion. Some alternative selection systems have been used in algae (the nitrate reductase selection system, uracil selection), but more research on alternatives for antibiotic selection of algae GMOs is necessary. Genetic deletion of the antibiotic selection gene after generation of a stable transgenic line has also been achieved for some algae transgenic systems, so technology to avoid antibiotic genes in GM-algae is under development (Mayfield, personal communication).

Table 4.4. Important data for environmental risk assessments of algae

Data

Effect

Strain identity

Pathogenicity, toxin production

Growth conditions

Spreading into the environment

Algae production system

Open pond, closed tubes

Specific GMO properties

Enhanced or reduced growth, antibiotic resistance

Stability of the GMO

Horizontal gene transfer

Harvesting method

Chance of escape

Notes

 
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