CHICAGO Scientists have found a way to ensure starter cultures used to make cheese can ward off attacks from bacteria-eating viruses -- a finding that could mean the difference between a great Gouda and wasted milk.
Attacks by viruses known as phages pose a particular problem for companies like Danish food ingredient maker Danisco, whose starter cultures are used in about half of all the ice cream and cheese produced in the world.
"Phages are one of the major causes of product failure for the food industry, especially in the dairy industry," said Philippe Horvath, a scientist at Danisco's laboratory in Dange-Saint-Romain, France.
The tiny viruses that infect bacteria enter the cell and rapidly replicate until the cell ruptures, spreading the virus in a series of repeating cycles.
"It's an explosive propagation," he said in a telephone interview.
Horvath and colleagues at Danisco have discovered how to harness bacteria's own natural defense mechanisms to produce phage-resistant bacteria. They reported their results in Friday's issue of the journal Science.
The study helps explain the role of a new family of repetitive sequences in the genome of bacteria called CRISPR sequences. They resemble some of the DNA sequences in the phages.
"LET NATURE DO THE WORK"
In computer models, scientists proposed that the CRISPR sequences allow bacteria to hijack a bit of the virus' genetic code, helping it to fight off attacks.
"Our results are the first biological demonstration that CRISPR provides a resistance against phages," Horvath said.
The researchers tested their theory on Streptococcus thermophilus, a bacteria used in making cheese and yogurt.
They were able to manipulate the DNA within the bacteria, adding a new spacer that gave it immunity against the attacking virus.
"We replicated what happens naturally in the lab using molecular biology tools. We've also shown that when we artificially take them out, the bacteria loses resistance," Horvath said.
Although the Danisco researchers could use the finding to produce genetically modified starter cultures for cheese and yogurt, they will not, out of respect for concerns over genetically modified organisms or GMOs in foods.
"We'll let nature do the work for us by simply challenging the bacterium with the phage," he said.
Then, they will simply choose the resistant bacteria for their cell cultures, he said.