In an early, acute stage of pneumonia, the pathogen employs a wide arsenal of weapons – so-called virulence factors – to invade the host and evade its immune system. During disease progression, the bacterium adapts its strategy by switching from acute to chronic virulence. It stops the production of virulence factors, such as bacterial injection apparatus and toxins and, instead, produces a protective matrix and reduces its growth rate. The environmental signals directing this transition were so far unknown. The team led by Prof. Urs Jenal, infection biologist at the Biozentrum of the University of Basel, has now identified calcium as a signal that specifically triggers the switch to chronic virulence.

“In Pseudomonas a central signaling pathway senses environmental information and ultimately determines whether the pathogen will undergo the acute to chronic virulence switch,” explains Jenal. “Although the components of this pathway are well-known, none of the external signals modulating the switch are defined.” The researchers have now discovered that a receptor located in the bacterial cell envelope monitors the calcium concentration in the environment and transmits this signal into the cell. Elevated calcium levels trigger the switch to a chronic program: The bacteria protect themselves within a biofilm structure, reduce their growth rate and by that increase their drug tolerance and persistence.

Cystic fibrosis patients harbor calcium sensitive bacteria