The process by which phages (viruses that infect bacteria and reproduce within bacteria) enter cells has been studied for more than fifty years. In a new study, researchers from the University of Illinois Urbana-Champaign and Texas A&M University used cutting-edge techniques to look at this process at the level of a single cell.
“The field of phage biology has exploded over the past decade as more and more researchers realize the importance of phages in ecology, evolution and biotechnology,” says Ido Golding (CAIM/IGOH), professor of physics. “This work is unique because we looked at phage infection at the level of individual bacterial cells.”
The process of phage infection involves the attachment of the virus to the surface of a bacterium. After this, the virus injects its genetic material into the cell. After entry, a phage can force the cell to produce more phages and eventually explode, a process called cell lysis, or the phage can integrate its genome into the bacterial genome and remain inactive, a process called lysogeny. The outcome depends on how many phages infect the cell at the same time. A single phage causes lysis, while infection by multiple phages results in lysogeny.
In the current study, the researchers wanted to ask whether the number of infecting phages that bind to the bacterial surface corresponds to the amount of viral genetic material injected into the cell. To do this, they fluorescently labeled both the protein coat of the phages and the genetic material within. They then grew Escherichia coliused different concentrations of infecting phages and kept track of how many of them retained their genetic material E.coli.
“We have known since the 1970s that when multiple phages infect the same cell, it affects the outcome of the infection. In this paper we were able to make precise measurements, unlike any other study done to date,” Golding said.
The researchers were surprised to find that the access of one phage’s genetic material could be hindered by the other co-infecting phages. They found that when more phages were attached to the surface of the cell, relatively fewer phages could enter.
“Our data show that the first phase of infection, phage entry, is an important step that has previously been underappreciated,” Golding said. “We found that the co-infecting phages hindered each other’s entry by disrupting the electrophysiology of the cell.”
The outer layer of bacteria is constantly dealing with the movement of electrons and ions that are crucial for generating energy and sending signals in and out of the cell. Over the past decade, researchers have begun to realize how important this electrophysiology is in other bacterial phenomena, including antibiotic resistance. This article opens a new avenue for research in bacterial electrophysiology – its role in phage biology.
“By affecting how many phages actually enter, these perturbations influence the choice between lysis and lysogeny. Our study also shows that entry can be influenced by environmental conditions such as the concentration of different ions,” Golding said.
The team is interested in improving their techniques to better understand the molecular underpinnings of phage entry.
“Although the resolution of our techniques was good, what was happening at the molecular level was still largely invisible to us,” Golding said. “We are considering using the Minflux system at the Carl R. Woese Institute for Genomic Biology. The plan is to investigate the same process, but apply a better experimental method. We hope this will help us find new biology. “
