Several traits of algae for biofuels may be modified through genetic engineering methods. Most are intended to increase biomass or oil productivity, though some could be designed to minimize survival or reproduction following release. Increasing productivity could involve objectives such as enhancing lipid content as a precursor to biodiesel (which could involve growing cells in nitrogen-deficient or silicon-deficient media), introducing biological pathways that permit direct production of fuels that need minimal processing prior to distribution and use, modifying cells to secrete feedstock or fuel directly into the culture medium, modifying carbohydrate metabolism in cells (increasing glucan storage, decreasing starch degradation), increasing tolerance to stressors (such as salt, light, pH, temperature, glyphosate) (Radakovits et al., 2010), and improving resistance to disinfectants. Some of these engineered traits and intended or unintended accompanying traits could affect either the suitability of algae for biofuel production purposes or their survival and physiology when released into natural systems. Phenotypic changes that could lead to potential major ecological effects of released organisms include those that result in increases in physiological tolerance or altered substrate use or that change the species’ geographic range (Tiedje et al., 1989).
Predictors of potential adverse effects of genetically engineered algae include probability of release, abundance of organisms released (predictor of establishment), survival rate and fitness, reproduction rate, probability of dissemination to distant sites, interactions with other organisms, probability of genetic exchange, and probability of an adverse effect (Alexander, 1985). New traits potentially can influence these factors, but few of these relationships are understood. Cell density in the culture medium could be affected by engineered traits. The scale and frequency of releases might determine whether the release leads to a self-sustaining (established) population (Tiedje et al., 1989). The survival rate of a genetically engineered microalga or cyanobacterium will be determined by a combination of the species identity, the genetic modification(s), and the environment to which it is released. Algae with high lipid content probably will be more attractive to predators. Some researchers suggest that most genetically engineered organisms will have lower fitness in receiving environments than unmodified organisms (Tiedje et al., 1989). Algae could be cross-bred or engineered to have high growth rates under specific culture conditions, and some of these might have high growth rates under specific natural conditions. New traits conferred on algae by genetic modifications would determine whether and how community interactions might be altered. Radakovits et al. (2010) pointed out that it is uncertain how genetically engineered strains will perform in scaled-up production systems with varying conditions and with wild-type competitive strains.
Genetic exchange might lead to unexpected effects. Snow et al. (2005) asserted that genetic exchange between recombinant microbes and indigenous microbes is probable. The three types of horizontal transfer are transformation of free deoxyribonucleic acid (DNA), conjugation, and transduction. The transfer of genes between microorganisms is common in some species (Snow et al., 2005). About 1 to 20 percent of the genomes of bacteria consist of DNA acquired recently (in an evolutionary context), predominantly from other prokaryotes but also from eukaryotes, for example, metazoa (Ochman et al., 2000; Koonin et al., 2002; Snow et al., 2005). Genetic exchange between prokaryotes and eukaryotes is not well studied (Rogers et al., 2007) beyond specific pairwise interactions such as T-DNA transfer from Agrobacterium species to plant cells (Gelvin, 2010). Some ancient, evolutionary scale transfers have been recorded. For example, a gene for plastidtargeted fructose bisphosphate aldolase was transferred from red algae to some Prochlorococcus and Synechococcus species (Rogers et al., 2007). Another study, for example, showed evidence for the horizontal transfer of a self-splicing, homing intron from a cyanobacterium