Researchers have discovered how bacteria such as E. coli get the essential nutrient iron during infection.

Scientists from Monash University in Australia found pathogenic bacteria obtain iron by pirating it from host proteins.

The protein import system of E. coli is an important factor in infections caused by pathogenic strains of this bacteria. Understanding how it functions will allow researchers to target and block it to combat such infections.

To grow and cause infection bacteria must get essential nutrients from their environments or hosts. Iron is one such nutrient and is often inside proteins, the building blocks of host cells.

Expanded knowledge
The study was led by Dr. Rhys Grinter from the Monash School of Biological Sciences, and professor Trevor Lithgow from the Biomedicine Discovery Institute. It was published this month in the journal PLoS Genetics.

“Bacteria that cause disease in plants can extract iron from plant proteins, by importing the protein and cutting it up once inside the bacterial cell. While it was known that these specific plant infecting bacteria can do this, it was unknown if other bacteria that infect humans and animals are also able to import host proteins,” said Grinter.

Researchers analyzed the genetic sequences of bacteria and found genes responsible for importing and processing proteins are widespread in those that cause disease in humans, animals, and plants. The team then characterized the protein-import systems in molecular detail, confirming their function.

These import systems are a channel through the membrane of the bacteria that imports iron-containing proteins and an enzyme inside that bacteria acts like a pair of molecular scissors. These scissors cut up the target protein once it enters the bacteria releasing the iron it contains so it can be used.

Diverse protein import systems
Scientists found the identified protein import systems are related to the virulent plant pathogen Pectobacterium, which targets iron-containing ferredoxin during infection. However, the study suggests these systems have evolved to target specific proteins present in the host of the bacteria they infect.

Iron-piracy is mediated by the ferredoxin uptake system (Fus), a gene cluster encoding proteins that transport ferredoxin into the bacterial cell and processes it. The study found gene clusters related to the Fus are widespread in bacterial species.

Grinter said it was previously unclear if the ability to import host proteins was widespread or not.

“We were surprised by how diverse and widespread these systems for protein uptake are. Our work suggests they are playing an important role in infection in many pathogenic bacteria.”

Researchers used X-ray crystallography and the Australian Synchrotron to determine molecular structure of the purified components of the protein-import system from pathogenic E. coli. They found protein import systems are widespread in Gram-negative bacteria.

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