In nature, most bacteria live on the bare minimum. If they experience nutrient deficiency or stress, they shut down their metabolism in a controlled manner and go into a resting state. In this stand-by mode, certain metabolic processes still take place that enable the microbes to perceive their environment and react to stimuli, but growth and division are suspended.
This also protects bacteria from, say, antibiotics or from viruses that prey exclusively on bacteria. Such bacteria-infecting viruses, known as phages, are considered a possible alternative to antibiotics that are no longer (sufficiently) effective due to drug resistance. Until now, expert consensus held that phages successfully infect bacteria only when the latter are growing.
Researchers at ETH Zurich asked themselves whether evolution might have produced bacteriophages that specialise in dormant bacteria and could be used to target them. They began their search in 2018. Now, in a new publication in the journal Nature Communications, they show that such phages, though rare, do indeed exist.
A lucky strike in a compost heap
When ETH Professor Alexander Harms and his team at the Biozentrum of the University of Basel began their project in 2018, they assumed that within the first year, they would be able to isolate around 20 different phages that attack dormant bacteria. But this wasn’t the case: it wasn’t until 2019 that Harms’ doctoral student Enea Maffei isolated a new, previously unknown virus. Found in rotting plant material from a cemetery near Riehen (Canton of Basel-Stadt), this virus can infect and destroy dormant bacteria. “This is the first phage described in the literature that has been shown to attack bacteria in a dormant state,” Maffei says. Harms adds: “In view of the huge number of bacteriophages, however, I was always convinced that evolution must have produced some that can crack into dormant bacteria.” They have named their new phage Paride.