GENETIC ENGINEERING

Bacteria

Bacteria and Genetic Engineering

1) Modern bacterial biochemistry and genetics rests largely on experiments in which we DO change the growth medium, generally in a very small way--such as by adding an inhibitor, removing a single mutrient, or adding an inducer or repressor of a single gene.

But some studies (including those in a sub-field in which I have been active) involve larger growth medium shifts, such as "downshifts" from rich to poor medium. The coherence of the whole, large experimental literature in all these areas depends on the stability of not merely the species, but the genotype of a particular clone used in the experiments. Indeed, labs all over the world routinely exchange specific clones in order to carry out experiments. In most cases, clones sent me from NIH, or Copenhagen, or Stockholm, or the New Haven E. coli strain repository, exhibit exactly the genotype they are supposed to.

Sometimes we streak out a culture AFTER doing an experiment, to confirm that the the culture did not suffer contamination by some other bug due to sloppy handling. Sometimes a small proportion of contaminants are found, particularly when an experiment is done by beginning students who are not competent in sterile technique. This almost never happens when the experiment is done by experienced people.

On the other hand, I can well imagine that if an incompetent who knows nothing about sterile technique messes about with bacterial cultures, from one day to the next a culture of one bug might become thoroughly contaminated with others from the incompetent's sweater or dandruff.

(2) We now have a vast, deeply interconnected body of information on the biochemistry, physiology, and genetics of some intensively studied bacterial species, such as E. coli, Salmonella typhimurium, and a few others. Our information extends to the complete DNA sequence of the chromosome and major plasmids, and the protein catalogue (size, location on a 2D gel separation, and abundance) of many of the genes' protein products.

This knowledge is so detailed that, if a fragment of a protein turns up in the wrong place (such as copurifying with another protein), all we need is a little of its amino acid sequence to look it up in the catalogue (via computer) to find out what the extraneous fragment is. In other words, our systematic knowledge of these species approaches the knowledge available about automobile species.

(3) Keeping that last point in mind, you may now consider the following thought experiment.

Suppose you bring your new Toyota Camry to the Brown Bear Car Wash. They send it through the building, and the attendant brings you a 1972 Ford Pinto, and tells you that your car mysteriously changed into a Pinto during the carwash. When he presents you with the bill, what do you tell him?

Cheers.
JON Jon Gallant
Dr. Phage Genetics Department
Grosser Seattle, Unltd.
University of Washington Seattle, WA 98195-7360 Phone: (206) 543 8235