In an effort to understand how best to combat the tooth-decaying properties of S. mutans, Brady and her team set out to learn how the organism was able to survive its own acid. To find out, the researchers tinkered with systematically turning off several genes, individually and in combination, to see how the bacteria responded.
"We found S. mutans can survive, with normal growth, without the SRP pathway," said Adnan Hasona, Ph.D., a research assistant professor of oral biology and the study's lead author.
The bacteria altered to lack SRP components were able to adapt and survive gradual increases in acid resulting from their own metabolism, suggesting a backup pathway was in place.
But, like goldfish dropped in new water, the altered bacteria could not contend with sudden environmental change. When artificially shocked with acid to a pH below that where tooth demineralization begins, the altered bacteria became sick and unable to grow. Shocking the bacteria with other environmental stressors, such as high salt levels or the presence of hydrogen peroxide, also caused them to weaken, Hasona said.
"So, at least in this organism, we learned the SRP pathway seems to enable it to respond rapidly to environmental stress, but it was not at all necessary for the organism's viability during non-stress conditions," Brady said.
Brady's team surmised that two other molecules, called YidC1 and YidC2, might be acting as alternate routes for protein delivery in the absence of the SRP pathway. They tested their hypothesis and found that S. mutans could continue to function in non-stress conditions without the SRP and YidC1 genes, but not without the YidC2 and SRP simultaneously.
Source:University of Florida