James and the Giant Corn Genetics: Studying the Source Code of Nature

Sorry for missing my daily post yesterday. Still trying to get over whatever I caught last week.

Last week, 13.3 million people watched CSI Miami in prime-time. That’s more people than live in the state Illinois. It doesn’t consider reruns, Tivo recordings, or piracy.** So to the untrained eye (mine), it seems likely the show is making enough money to hire a scientific consultant or two. Clearly the untrained eye is wrong and budgets are so tight that that the expense of finding someone who’d taken intro biology anytime in the past fifteen years was far too much. As demonstrated in this weeks episode “Bad Seed.”

Before I continue, let me say first of all I’m not one of CSI:Miami’s regular viewers. They don’t have to worry about losing me as a fan. I never was one. Second, I don’t get angry when shows like Fringe or the SyFy (<–that’s really how they spell their name now) Channel’s disaster and/or monster movie of the week completely mangle science. They are, and acknowledge themselves to be, science fiction. Shows based on fictional science. On the other hand, shows such as the CSI and Law&Order families set fictional stories in what, we are supposed to believe is, the  real world. As such, the burden on them to get their facts straight is much stronger.

A burden the writers of CSI Miami clearly can’t be bothered to live up to. (Oh, if it wasn’t obvious already, spoilers ahead).

The plot goes like this: A woman comes into the hospital and then dies, afterwards they discover her body tests positive for e. coli and conclude she died of food poisoning. Then her boyfriend also gets sick and becomes paralyzed. The strain of e. coli that caused her death is traced to an organic farmer whose irrigation water is contaminated with excrement from a local cattle farm. It turns out the boyfriend ate sweet corn from the same farm that was genetically engineered to produce an enzyme that breaks down cellulose to make corn kernels more digestible. Except the enzyme was isolated from a species of bacteria related to Clostridium botulinum, the bacteria that makes botulin, the toxin that can kill people who eat improperly prepared foods and is used to make old people’s faces less expressive through controlled paralysis (botox). So through the magic of bacteria conjugation, the fictional transgenic corn will occasionally start producing toxin, killing whoever eats it.

Let’s take it apart step by step shall we?

1. Her body tests positive for e. coli, therefore she was killed by food poisoning! Unfortunately for the logic of the story, I defy you to find a person who wouldn’t test positive for e. coli. The bacteria can be found in the gut of almost every warm blooded animal. Mostly it’s harmless, which is why a diagnosis of the e. coli as causing the food poisoning would require a bunch of cases with each person carrying not just e. coli, but the same exact sub-strain of the bacteria. Otherwise it’s impossible to tell normal e. coli living in symbiosis with the human body from new pathogenic (disease causing) e. coli.
2. We found e. coli on the farm therefore this is the source of the infection. As mentioned above, almost any farm will have e. coli present at some level, especially organic farms that get their fertilizer from animal excrement that has (by definition) recently been in the gut of a warm blooded animal, primarily cows and pigs. That’s why the key to the recent outbreak of food poisoning from spinach was the identification of the same sub-strain of e. coli (O156:H7) on a farm owned by Mission Organics, as had sickened more than 200 people across the country, killing 5 of them.
3. Breaking down cellulose makes sweet corn more digestible, so let’s put in a trans-gene to do that. Yes, people can’t digest cellulose. That’s why even if you are starving you shouldn’t try to eat grass. It will likely make you throw up, which will put your body in even worse shape. However since we as a species have had to survive for millions of years, we’ve learned to eat foods we can digest because instead of cellulose their energy is stored as sugars, carbohydrates or protein. Everything from soybeans, to eggplant, to corn. Corn kernels are full of energy to fuel a new corn seedling. Plants can’t extract energy from cellulose any more than we can (plants use cellulose as a building material, not to store energy), so the energy a plant gives to its offspring has to be in other forms, like starch and oil that are as useful to people as they would be to the seedling. Unless people suddenly start munching on corn cobs or chewing corn leaves, being able to digest the cellulose in corn isn’t going to make corn better to eat.  (The only reason I can think of to want to express a cellulose digesting enzyme in corn would be for biofuels production, and the episode clearly states that the trans-gene was to make corn better to eat and feed people.)
4. Since we took a gene from a species related to the one that produces botulism toxin, the corn we put the gene into could start producing botulism toxin (or anything else the bacteria or any of its relatives produce) at any time. One gene->one RNA->one protein.*

I’m going to break out of the list format here, because I have a lot to say about point 4. A gene is an individual part of the genome a living thing inherits from its parents. Different genes within the genome contain the code needed to make a singe protein that performs some function in the cell.

Think of the genome as an engineering library. Each gene is a book (with blueprints) about how to make a single machine from a universal set of parts found in every living cell. People from the town around the library (the rest of the cell) come in, make photocopies of books, and using the copies to build all the different machines they need. Through inter-library loan (genetic engineering) a book on how to build a rototiller arrives from a second library. Now the people in the town around the first library (the rest of the cell) know how to make rototillers and can use this new machine to turn over laws that they’ve decided to replant with vegetables and native prairie plants.

The book on how to make rototillers was previously stored in the second library as a book on how to build patriot missiles, but that doesn’t mean that getting the book on rototillers will tell the cell how to build missiles. Even if the second library messes up and sends the book on patriot missiles instead of the book on rototillers, it will be immediately obvious since its easy to check whether there’s a book on how to build a rototiller on the shelves(checking the DNA sequence), check for the presence of rototillers themselves around the library(checking for the protein),  and even look for whether land is getting churned up so new things can be planted (assays for activity of the protein). The town fails any of these checks, the scientist knows something was wrong (whether the wrong book was sent, or it was damages in transit, or put somewhere deep on the shelves where no one could find it), and he or she will get rid of the failed experiment and start over.

(Sorry that took so long but the problem with the truth is that it’s usually more complicated to explain than a well crafted lie.)

In summation genes only do single, specific things. The made-up cellulose digesting enzyme of CSI Miami is encoded for by a single  (also made up) gene, botulism toxin by another gene somewhere else in the genome. After a gene is moved, you check to make sure the gene is what you think it is, and it’s doing what you expect it to be doing. There is absolutely no way moving a gene that tells a plant how to degrade cellulose could make a plant produce botulism toxin. Plants don’t know how to make that toxin, and unless someone specifically puts the gene that encodes for botulism toxin (not anything else) into them, they can’t learn how to.

It’s a stupid and easily catchable error from a show that claims to show fictional stories set in the real world. I haven’t touched any of the various evil characters the show had trying to cover up the evil toxic corn. The crime on these shows is supposed to be fictional. If they decide they want to make farmers, seed companies, and government regulators look bad, that’s their business. But when they mislead people about the fundamental science behind their stories that I and people like me will have to work hard to fix, as a Graduate Student Instructor, as (hopefully one day) a professor or lecturer, and as a scientific advocate online (what I’m doing right here).

*This is called the central dogma of biology. Which is a horrible term because it’s not dogma in the religious sense. Scientists celebrate finding exceptions to the rule, like ribozymes which are RNAs that are encoded by genes but instead of making a protein ribozymes perform some task in the cell themselves.

**Although I hope anyone smart enough to figure out how to illegally download off the web is smart enough to see the problems with this weeks episode