Transgenic Bt Technology: 6. Biosecurity
Prof. C. Kameswara Rao
Foundation for Biotechnology Awareness and Education,
Bangalore, India krao@vsnl.com, www.fbae.org, www.fbaeblog.org

Biosecurity has two components:  a) Biosafety, the safety of GE products to humans and animals as food, feed and medicine, and b) Environmental safety, the safety of non-target organisms, soil and water.  The terms biosecurity and biosafety are often used incorrectly as synonyms.  

Raised from both the pro-tech and anti-tech platforms, biosecurity issues are relevant even to products of classical agricultural biotechnology, but were never made an issue in that context.  

Science has answers on all biosecurity concerns.   The regulatory process ensures that all questions are answered reasonably satisfactorily.

Biosafety of Bt:

Bt being a universally occurring soil bacterium, all species of plants and animals in agricultural and other situations, and those that use plants as food have been exposed to Bt and Bt toxins for centuries.   Bt toxins are transient in the environment (http://www.fbae.org/Channels/Views/transgenic_bt_technology.htm).  The toxicity of Bt proteins is pest specific, dependent upon a set of biological pre-requisites (http://www.fbae.org/Channels/Views/transgenic_bt_technology.htm).   The use of Bt as a conventional pesticide for over 60 years has demonstrated that it is safe to a variety of non-target organisms.   Cry proteins were shown to be harmless to vertebrates, including mammals and humans, even at high doses, by ingestion, inhalation or injection.

Bt is one of the few pesticides recommended for widespread application in North America, and was broadcast or sprayed on crops and air sprayed to control forest pests in Utah (US, 1990-1995) and Ontario (Canada, 1985-1994).   Water borne Bt was air sprayed to control the Asian gypsy moth in Vancouver (Canada, 1988), and North Carolina (US, 1993) and the white-spotted tussock moth in Auckland (New Zealand, 1996).   No greater testimony is needed for human safety of Bt than that no adverse effects on the human population in these urban locations have been reported so far.  

Toxicity and allergenicity:

The issues of toxicity (http://www.fbae.org/Channels/Views/Misuse_of_science.htm, http://www.fbae.org/Channels/Views/TOXICITY_OF_GM_food.htm) and allergenicity (http://www.fbae.org/Channels/Views/not_allergic.htm) of Bt proteins were already discussed on this site.   GE products cannot be toxic or allergenic if the recipients of the transgenes were not.

Impact of Bt on non-target organisms:

Glare and O’Callaghan (2000, http://www.fbae.org/Channels/Views/transgenic_bt_technology.htm), and every country’s regulatory process provide extensive data demonstrating the safety of Bt toxins to non-target organisms.  

The much-brandished instance of toxicity of Bt proteins to non-target organisms relates to the study by Losey, et al.,  (Nature, 1999) who reported that transgenic Bt corn pollen harm monarch larvae, a conclusion immediately questioned by Hodgson (Nature Biotechnology, 1999).   Subsequently, Sears, et al., (Proceedings of the US National Academy of Sciences, 2001) re-examined the issue, avoiding the flaws in the experimental design in the study of Losey et al., and concluded that impact of Bt corn pollen on monarch butterfly populations was not significant.  

Vertical gene flow:

The essential pre-requisite for vertical gene flow is sexual reproduction between the transgenics and related plants.   The transferred genes express only in the next generation.   The ease of vertical gene flow depends upon the genetic relationships between the varieties and whether the crop is self or open pollinated, which Bt technology cannot change.   Transgenics are no more promiscuous than their isogenics.   If vertical gene flow were possible between isogenics and any related varieties or species, it would be so between transgenics and related plants too.   Centuries of agricultural experience does not indicate any such possibilities.   

A study, much quoted by the critics on the risk of vertical gene flow, relates to Bt maize in Mexico.   David Quist and Ignatio Chapela, (Nature, 2001), reported the presence CaMV 35S promoter and a Bt gene, ‘traced’ to Bt maize, in native maize populations in Oaxaca, Mexico.   They claimed that the genes got incorporated into the native land race.   Worse is that the promoter was attached to different gene sequences in different samples, an alarming situation since it means that the promoter is out of control and may activate any other genes.   The scientific community challenged the methodology and the conclusions, which lead Nature to announce that it should never have published the paper.   Snow et al., have analyzed 1,50,000 corn seeds collected during 2003-04, from 125 fields at 18 locations, in the State Oaxaca, Mexico, the same area as of Chapela’s study, and found no evidence of the transgenes in native maize populations (http://www.pnas.org, August 5, 2005).   The defense can be that the genes were there in 2001 and vanished subsequently!

Lateral/horizontal gene flow:
Lateral/horizontal gene flow involves exchange of genes between genetically unrelated organisms, a fact of evolution, but not of day-to-day occurrence.   It does not involve sexual reproduction and the transferred genes can express in the same generation.   Transgenic technology itself is an example of lateral gene transfer.   All known examples of lateral gene transfer relate to endoparasites and their hosts, as for example, the commonality of about 30 per cent of genes between mammalian intestinal parasites and their hosts.   

The use of antibiotic markers in transgenic technology, to confirm genetic transformation, has raised the fear that if there were lateral transfer of antibiotic resistance genes to pathogenic organisms, it would breed pathogens resistant to the antibiotics used as markers.   This may endanger our prospects in the fight against pathogenic bacteria.   While no proof exists on this assumption, the use of anitbiotic resistance marker genes is now minimized, as alternatives are found.   The antibiotic marker genes can also be removed, after confirming genetic transformation.

How safe are Bt transgenics?

All the evidence indicates that Bt transgenics are very safe and a decade’s cultivation of Bt transgenics has neither confirmed the scary possibilities aired by the critics nor has thrown up any new threats.    Biosecurity issues are often mixed up with political, economic, management, societal and ethical issues, emotionalizing and sensationalizing the concerns, to spread fear and suspicion of GE technology.  

September 16, 2005