Laboratory contaminants likely explain the results of a recent study claiming that complete genes can pass from foods we eat into our blood, according to a University of Michigan molecular biologist who re-examined data from the controversial research paper.
Dr. Richard Lusk said his findings highlight an underappreciated problem – contamination of laboratory samples – with one of the most popular and powerful new tools of the discipline: high-throughput sequencing, in which the exact sequences of billions of pieces of DNA are determined simultaneously.
Lusk said the technique has generated some extraordinary biological insights, as well as a few puzzling results, including a July 2013 paper in the journal PLOS ONE concluding that complete genes from some of the foods we eat – including tomatoes, soybeans, rice and corn – manage to survive digestion intact and make it into our bloodstream.
That online paper, by Sandor Spisak of Harvard Medical School and his colleagues, has received more than 53,000 page views and has been shared on social media more than 5,400 times. Lusk reanalyzed the experiments behind that claim and relates his findings in a paper published online Oct. 29, 2014 in the same journal, PLOS ONE.
"When I examined the original data from the paper claiming that genes pass from food to blood, I did find food DNAs," said Lusk, a research fellow in the U-M Department of Ecology and Evolutionary Biology.
"But I also found much higher quantities of DNA from common skin microorganisms, suggesting that at least some of the DNA in the sample came from contaminants. Maybe the food DNA got there the same way."
One of the microbes Lusk found, the bacterium P. acnes, is linked to the skin condition acne. Another, the fungus M. globosa, causes dandruff.
Though he did not investigate the possible sources of the contaminants he found, Lusk said that one scenario that could explain the presence of both the food and microbial DNAs is that various laboratory workers contaminated sample tubes after touching their faces, scratching their heads, and eating.
"But in this case, the scientists behind the study performed reasonable controls and took appropriate precautions against contamination," Lusk said. "Could contamination really be the answer?"
Spisak and his colleagues argued that DNA from food made it into human blood plasma. Lusk reasoned that if he examined DNA from sources with no plausible connection to food and still managed to detect the signals of food DNA, "then those signals must necessarily derive from contamination."