( Dr. William Navarre a senior fellow at...)Bacteria have their own immune system protecting against outside DNA

The researchers also learned that the H-NS protein is able to recognize foreign DNA on the basis of its increased content of adenine and thymine, the building blocks of DNA.

"It has been a great mystery why disease-causing genes of bacteria usually contain more adenine and thymine," said Michael McClelland, professor and director of the Molecular Biology Program at the Kimmel Cancer Center. "Now we know this is because such sequences are easier to recruit and regulate than other DNA."

This research could also have major implications for the biotech industry, which uses bacteria for the production of recombinant proteins for medicine and research. These proteins, such as insulin or human growth hormone, are created when a piece of human DNA corresponding to that protein is introduced into bacteria. The bacteria then reproduce many times over, creating more of the protein each time they reproduce. The proteins are purified out from the bacteria, leaving behind only the useful protein. However, in that process, the yield of some human proteins produced in bacteria can be low. The new research indicates that the H-NS "immune system" may be responsible for interfering with the expression of human genes in bacteria.

"Having a better understanding of this system could help the biotech industry make recombinant proteins more efficiently," said Fang. "More foreign protein can be produced in bacteria that don't have the H-NS molecule."