From hard drives to flash drives to DNA drives.

Recently there has been another round of controversial news regarding genetically modified organisms (GMO). Perhaps the best known debate on these centers on corn. A recent French study showed severe kidney and liver abnormalities in rats that were fed this corn for up to 2 years. Immediately afterward, Russia banned the use of this seed and the corn it produces. Because other studies have not confirmed this finding, the American media immediately released news stories stating that the French study was flawed and unscientific and that it represented just another round of propaganda by individuals who oppose GMO and the companies that produce the seeds (which are mostly American). Salmon, with growth hormones that have been altered so that they not only grow faster but never stop growing, has also been in the news. Salmon is the third most-eaten seafood in the United States according to the National Fisheries Institute, and most of it is flown in from Chile, so growing enough of it here to feed Americans may actually be a good thing for the environment, even if its genes have been modified. All of these situations involve inserting or altering a specific gene in plant or animal deoxyribonucleic acid (DNA); thus, the genetic material in those organisms still serves its original purpose. However, what happens if we take our DNA, reconfigure it, and use it for something completely different from that for which it is intended? Cuttingedge genetic engineers are now synthetizing DNA so that it contains information much like a computer hard drive or solid memory chips. The capacity of DNA as a storage medium is staggering: All of the information contained on the entire Internet would fit into a device smaller than 1 cubic inch! As our need for high-capacity information storage continues to increase, several researchers have begun to explore the possibility of using DNA for this purpose. The very fabric of life uses a binary code, but instead of the 1s and 0s computers use, the code in our DNA is composed of 4 letters: A, G, C, and T (adenine, guanine, cytosine, and thymine), which are paired into 2 nucleotide bases: A-T and G-C (hence a form of binary code). By changing the order of these 2 base nucleotide pairs, one can encode all different types of information in the same way a computer does by changing the order of 1s and 0s. Each nucleotide may encode 2 bits of information, and 1 g of single-stranded DNA can store 455 exabytes. One exabyte is equal to 1000 petabytes; 1 petabyte is equal to 1 quadrillion bytes, and so on. What this means is that in 1 g of single-stranded DNA, one can potentially store the equivalent to 250 million DVDs! Computer chips are “planar” storage devices (obvious from their shape). One way to improve the capacity of a computer chip is to put several layers of circuits in it (making it 2D), but because DNA is 3D, it offers much more space. Memory cards are said to be reliable for up 5 years after their initial use, but DNA-encoded information remains stable and readable for millennia. For purposes of timeless storage, DNA may be dried and then protected from water and oxygen, which gives it a nearly infinite stability. DNA information storage is not new. It has been around since 1988, and one of the first successful projects came from the J. Craig Venter Institute, a nonprofit genomics research organization with facilities in 3 different US states. These investigators were able to encode 7920 bits into DNA. (Pridefully, in a synthetic cell, they encoded their names, 3 literary citations, and the address of an Internet site [Table].) Newer DNA-synthesizing techniques can alter the way base nucleotide pairs are formed, making it easier to encode information and thereafter read it. As mentioned previously, traditionally base pairs are A-T and G-C (remember that nucleotides are measured in pairs because DNA is usually double-stranded). Thus, the number of base pairs is equal to the number of nucleotides in 1 DNA strand. The problem with using the natural sequence of nucleotide base pairs for information encoding is that the G-C pair can be difficult to subsequently read. Therefore, new techniques use novel base pairs: A-C and G-T, which are easy to manufacture and thereafter interpret. With these 2 new base pairs, one also has a binary code: A-C for 0 and G-T for 1. At present, assembling long stable strands of DNA is difficult, so information needs to be parceled in smaller data blocks of DNA called “oligonucleotides ” (by comparison, the human genome contains about 3 billion base pairs, so it is a very long strand and the amount of information that it contains is astonishing). In a recent experiment, Church et al took one of their own books (nearly 54,000-words-long, including 11 images) and used a computer to convert it into a bit stream (they initially thought about encoding Moby Dick). They encoded all of the bits of the book into 159 oligonucleotides, each also containing information as to its general position within the text. The encoded DNA was then amplified by polymerase chain reaction* (PCR), and in this way, its base pairs could be assessed, read, and interpreted (similar techniques were used to map the human genome). During the entire process of writing, amplifying, and reading 5.27 megabits of information, only 10 bit errors occurred, a testament to how incredibly exact this technology is. Church et al were able to store in DNA 600 times more information than was previously possible. As amazing as this seems, one must add to it the fact that this technique used only in vitro procedures, avoiding the controversies of cloning and live genetic manipulations, and it was 100,000 times cheaper than other previous versions. Synthetic DNA is exempt from the National Institutes of Health usage guidelines and is available to all with the means to http://dx.doi.org/10.3174/ajnr.A3482