Indian researchers have found a new target that can potentially be used for developing new antibiotics that will be effective against many bacteria. The new target is made of two proteins, which form a complex that is responsible for the formation of biofilm, that perform very important functions and are critical for bacterial ability to successfully infect humans. The results were published in the journal Biofilms and Microbiomes.
Biofilm as a biological shield
Bacteria form biofilms, a kind of matrix, during infection in plants and animals. The biofilm shields the bacteria from antibiotics and helps bacteria survive harsh conditions such as extreme temperature or stress. Now a study by Indian researchers has found the molecular signalling events that play a crucial role in biofilm formation in Bacillus anthracis, the causative agent of anthrax.
Till now, all attention has been on developing antibiotics that target disease-causing bacteria and not the biofilm itself.
One of the basic questions that scientists have been trying to answer is how and when bacteria decide to form biofilms. “One possibility is that bacteria has sensors on the surface which senses some signal and helps in biofilm formation,” says Andaleeb Sajid from the Institute of Genomics and Integrative Biology (IGIB), Delhi and one of the authors of the paper.
“It was serendipity. Our lab was working on signalling in bacteria and we were studying PrkC and similar proteins. When PrkC protein is deleted, Bacillus bacteria are unable to form biofilm. So we started studying the mechanism by which PrkC protein controls biofilm formation,” she says.
“Our hypothesis is that PrkC senses some signal and transmits it from outside to inside the cell. This signal goes to other proteins like GroEL. PrkC adds phosphate group (phosphorylate) to different proteins. The mystery to biofilm formation lies with one chaperone protein called GroEL. The addition of phosphate to this tiny machine initiates a course of events within bacterial cells leading to complex biofilm formation,” Dr. Sajid says.
GroEL protein’s role
The team found several proteins receive signals from PrkC protein. Using cutting edge genetics, molecular biology and proteomics techniques, they confirmed that GroEL was regulated by PrkC.
“From other unrelated bacteria, we already had a clue that GroEL has a role in biofilm formation. We looked at the molecular level and found six amino acid residues where phosphate was getting added to the GroEL protein. Through a series of steps, we ascertained how important phosphorylation was for proper functioning of GroEL,” says Gunjan Arora from IGIB and the first author of the paper.
“We wanted to know if the bacteria has any other compensation mechanism to form biofilm in the absence of PrkC. So we made PrkC mutant bacteria to produce more of GroEL. The bacteria were able to form biofilm even in the absence of PrkC. This experiment helped us understand that PrkC is the influencer and GroEL is key to biofilm formation,” Dr. Arora says.
Both PrkC and GroEL perform very important functions and are critical for bacterial ability to successfully infect humans. “We think GroEL-PrkC complex could be a target for developing new antibiotic that will be effective against many bacterial pathogens such as the ones that cause MRSA, TB and pneumonia. One strategy to tackle drug resistant bacteria will be to develop multi-drug regimen that combines traditional antibiotics with candidate drugs that can block bacterial signalling and prevent biofilm formation,” Dr. Arora says.
