(Calothrix) to the chloroplast genome of Euglena myxocylindracea (Sheveleva and Hallick, 2004). Gene transfer between dissimilar organisms is possible, though rare. There is evidence that nuclear genes encoding chloroplast proteins have been transferred from an alga to an ascoglossan sea slug that consumes the algae (Pierce et al., 2003). Horizontally transferred genes can code for selectable traits, such as antibiotic resistance, pathogenicity, and metabolic enzymes (Snow et al., 2005). Horizontal gene transfer depends on the density of organisms with which exchange is possible.

The principal adverse effects of any algae, whether genetically engineered or not, could include health and ecological effects from toxin production, ecological effects from blooms, and species replacement. These potential effects are discussed elsewhere in this report. The potential propagation of antibiotic resistance markers also would be a concern, but species containing these markers would unlikely be used for commercial-scale production of biofuels. Toxin production by genetically engineered algae is unlikely because toxin-producing strains would be avoided, or strains probably would be engineered to remove toxin genes. A genetically engineered strain might have a lower risk of adverse impact than a natural strain that has not had such modifications. Categories of potential ecological risks from genetically engineered organisms that were highlighted by Tiedje et al. (1989) and Snow et al. (2005) would need to be considered in assessments of released algae. These include creating new or more effective pathogens, affecting nontarget species, disrupting biotic communities and ecosystems, reducing biodiversity or species-genetic diversity, or degrading valuable biological resources, many of which are discussed in the section on invasive species. Little evidence is available to evaluate the potential for any of these effects. Species that are genetically engineered to become more tolerant of environmental stressors, such as salt or temperature, could bloom in habitat conditions where blooms previously have not occurred. Species replacement is a potentially delayed effect (Tiedje et al., 1989). Whether exposure to genetically engineered organisms or genetic exchange with these organisms poses any potential hazards depends on the particular traits of the organism (Snow et al., 2005).

Most approaches to risk assessment suggest that familiarity with genetically engineered organisms is an important predictor of risk (Efroymson, 1999). That is, genetically engineered organisms that have a history of safe use in applications similar to proposed uses (for example, at similar densities in similar ecosystems) would not be likely to threaten environmental sustainability of algal biofuels. Similarly, microorganisms that are not developed from dissimilar source organisms but rather are created from closely related organisms (see EPA, 1990) are less likely to have new traits and to cause adverse effects.

5.8.2 Social Acceptability of Genetically Engineered Algae

If algal biofuel companies are moving toward the use of genetically engineered algae, popular and political resistance could be anticipated. Some concerns over genetically engineered algae depend on the capability of these algae to survive and invade natural environments (as in the case of invasive algae) outside a production environment where temperature, nutrient loads, salinity, and pH all can be optimized. People have expressed concerns regarding the release of genetically engineered microorganisms, ranging from impacts of large-scale releases (and failure of control mechanisms) on biodiversity to ecosystem and evolutionary processes (Hagedorn and Allender-Hagedorn, 1997). Other concerns regarding genetic technologies relate to the unnaturalness of organisms (Tenbult et al., 2005; Connor and Siegrist, 2011); these cannot be abated through technical mitigation. It is the public

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