This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: During infection, bacteria encounter rapidly changing and stressful environments inside the body. To understand how they adapt, researchers often measure messenger RNA (mRNA), which carries information from genes that can be translated into proteins.
While mRNA levels are widely used to monitor bacterial responses, proteins carry out much of the work inside the cell and are influenced by processes that occur after RNA has been produced. Scientists have long known that mRNA levels do not perfectly predict protein abundance. What has remained unclear is how that relationship changes under different stresses and across different bacterial pathogens.
In a new study published in the Proceedings of the National Academy of Sciences, researchers compared three human pathogens: Salmonella enterica Typhimurium, Yersinia pseudotuberculosis and Staphylococcus aureus. By exposing them to 10 infection-relevant conditions, they investigated whether the relationship between mRNA and protein levels was species-specific or broadly shared. Across all three species, mRNA and protein levels generally followed the same trends.
However, stresses that triggered the largest changes in gene and protein expression also showed the weakest agreement between RNA and protein levels. In other words, under some of the most challenging conditions, RNA provided a less complete picture of what was happening inside the cell. "When bacteria receive a sudden warning from their environment, they immediately start changing the messages inside the cell about what needs to happen next," says Sena Gizem Süer, a doctoral student in the Department of Molecular Biology and a member of Stress Response Modeling at IceLab research school at Umeå University and shared first author of the study.
"The cells can change their plans faster than they can build the things needed to carry them out." One stress condition stood out: osmotic stress, which occurs when changes in the concentration of dissolved substances around a cell disturb its water balance. Pathogens can encounter such environments in the body, for example, in the gut lumen. Genes responding specifically to osmotic stress showed a particularly weak match between mRNA and protein levels in all three bacterial species.
To investigate why, the researchers combined computational analyses with laboratory experiments. Their analyses pointed to altered translation, the process in which ribosomes read mRNA and build proteins, under osmotic stress. The experiments confirmed that bacteria continued to translate mRNA into proteins during osmotic stress, but at significantly reduced levels in both Yersinia and Salmonella.
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