Centre for Integrated Research in Biosafety

10 May 2011

Setting the record straight on monitoring gene transfer from GM animals

The spokesperson for AgResearch made factually incorrect statements to Radio New Zealand’s “Rural Report” on 9 May 2011. He was challenging the peer-reviewed and published results from the Centre for Integrated Research in Biosafety (INBI) which found fundamental flaws in the monitoring of horizontal gene transfer from genetically modified animals disposed of in offal pits. Of concern to us was this statement:

“…soil bacteria are normally only found in the top soil layer which is several centimetres in depth which actually contains oxygen and biological matter so we focussed our sampling at a depth to which soil bacteria are actually found and were there any transfer it would take place in that zone where the bacteria were.”

Our response:
1. Soil bacteria and other microorganisms can be found many metres below the soil surface. Microorganisms have been detected in oil reservoirs 3000 metres deep, with metabolically active bacteria found well over 1000 metres deep (Mason et al., 2010). Notably the statement above is contradicted by AgResearch’s own research. In 2004 AgResearch detected over a million aerobic and culturable bacteria per gram of soil at its single deepest sample of 5.5 metres.

2. While the numbers of cellular microbes does decrease with depth, microbes are not absent but are still found in substantial numbers. The number of microbes in topsoil near the surface reaches an estimated 2 billion per gram of soil (Heinemann et al., 2011, Heinemann and Traavik, 2004). At depth, the population reduces by as much as 2/3rds (Fierer et al., 2003) but remains just under 1 billion per gram of soil. Indeed, an estimated 35% of the microbial biomass in the top 2 metres of soil resides below 25 centimetres (Fierer et al., 2003), and thus it is especially poignant that AgResearch mainly sampled at only 15 and 30 cm, thus ignoring a significant proportion of the potential recombinant population.

3. Microbes on and inside the discarded carcasses would have seeded populations of bacteria and other microbes at depth, at numbers that potentially exceed those at surface. These microbes would have been of the highest priority to sample because they would have been in longest contact with the animals.

4. The kind of microbes at depth may differ in proportion from those near the surface. It is again noteworthy that AgResearch restricted their survey to only bacteria, only bacteria that can be cultured, only bacteria that can be cultured in an oxygenated environment, and only those in the top soil layers not in contact with the animals, and thus AgResearch actively excluded from consideration an estimated 99-99.9% of all other kinds of bacteria and 100% of all other kinds of microbes.

5. There is no evidence to support the contention that transfer would be restricted to the top soil layers. It is in fact probably impossible for transfer to take place in the top 30 cm when the genes being monitored were at least 1.7 vertical metres lower. This equates to approximately 1.7 million bacterial body lengths away. With the exception of one self-described “preliminary experiment” in 2004, AgResearch sampled for gene transfer in soil that essentially could not contain the target genes.

Prof. Jack A. Heinemann
Dr. Brigitta Kurenbach
Ms. Nikki Bleyendaal
Centre for Integrated Research in Biosafety
University of Canterbury

References
Fierer, N., Schimel, J. P. and Holden, P. A. (2003). Variations in microbial community composition through two soil depth profiles. Soil Biol. Biochem. 35, 167-176.

Heinemann, J. A., Kurenbach, B. and Bleyendaal, N. (2011). Evaluation of horizontal gene transfer monitoring experiments conducted in New Zealand between 2004 and 2009. J. Org. Sys. 6, 3-19.

Heinemann, J. A. and Traavik, T. (2004). Problems in monitoring horizontal gene transfer in field trials of transgenic plants. Nat. Biotechnol. 22, 1105-1109.

Mason, O. U., Nakagawa, T., Rosner, M., Van N., J. D., Zhou, J., Maruyama, A., Fisk, M. R. and Giovannoni, S. J. (2010). First investigation of the microbiology of the deepest layer of ocean crust. PLoS Biology 5, e15399.

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