Researchers examining bacteria from freshwater environments and soil have identified a crucial protein involved in preserving the shape of these microorganisms. This discovery is significant since maintaining the integrity of a bacterial cell’s protective shell is vital for its survival, potentially leading to the development of new and improved antibiotics.
In what they termed a “surprising” finding, Johns Hopkins Medicine researchers have uncovered the important role of a protein in sustaining the shape of harmful bacteria. As the structure of a bacterial cell’s protective layer is crucial for its survival, this discovery may help pave the way for the creation of new and more effective antibiotics.
Described in a study published on August 15 in the journal mBio, the research indicates that the loss of a protein known as OpgH in a commonly studied bacterium, Caulobacter crescentus, triggers a chain reaction that compromises the bubble-like protective layer surrounding the bacterium, ultimately leading to the death of the cell. OpgH is an enzyme involved in producing glucose-based molecules called osmoregulated periplasmic glucans, or OPGs, which occupy the gel-like spaces of the protective cell layer.
“In our experiments, when we eliminate the OpgH protein in Caulobacter bacteria, which stops the production of OPG sugar molecules, the bacteria cannot survive,” explains Erin Goley, Ph.D., the senior author of the study and a professor of biochemistry at the Johns Hopkins University School of Medicine.
Although Caulobacter crescentus itself is generally not harmful, OPGs found in abundance in gram-negative bacteria—those encased in a shell-like membrane—play a significant role in antibiotic resistance and disease progression.
This highlights the importance of further exploring the function of these sugar molecules in gram-negative bacteria, including Caulobacter, as a means to develop new drugs targeting harmful bacteria that possess OPGs, such as Brucella, Pseudomonas, Salmonella, and E.coli.
According to Goley, if it is true that the proteins responsible for creating or transforming these sugar molecules are vital for bacterial survival, they may serve as effective targets for antibiotic development. Alternatively, in bacteria where OPGs are not crucial, a drug aimed at part of the OPG production pathway might make the cells more susceptible to existing antibiotics.
In this research, the scientists utilized a molecular tool known as an inducible promoter to reduce the amount of the OpgH protein in Caulobacter, allowing them to observe the effects on the bacterium’s shape and how the loss of OpgH impacts a signaling pathway called CenKR, which detects and repairs issues in the cell envelope. They also increased the production of the protein CenR to activate the CenKR pathway that regulates cell shape.
After adjusting the levels of OpgH or CenR proteins, the scientists placed the bacterial cells on a gel pad that restricted their movement, then employed a specialized microscope to examine their shapes and behaviors.
“We observed that the bacteria became deformed when we reduced the amount of OpgH protein, stopping OPG sugar production, or when we hyperactivated the CenKR signaling pathway, which maintains the cell envelope,” Goley states.
“We also investigated the locations of various molecular components that help grow and maintain cell shape. Their incorrect positioning indicated that OpgH and CenR are essential for keeping the cell’s shape intact,” she adds. “When the cell envelope becomes distorted, the bacteria eventually rupture and die.”
“We created a model for how depleting OPGs or activating the signaling pathway affects both the shape and growth of the cell,” Goley notes.
While determining the role of the sugar molecule in Caulobacter‘s cell composition is a crucial initial step, Goley warns that “it will take some time to develop a comprehensive understanding of their function in various gram-negative bacterial species.”
In Caulobacter, these sugar molecules appear as closed rings, while in E. Coli, they resemble tree-like structures, with branches attached to chains. Gaining insight into their shape and associated components may aid researchers in characterizing the cell envelope more precisely.
“In the next phase of our research, we aim to explore all the enzymes involved in creating, modifying, and breaking down these molecules so that we can gain a comprehensive understanding of their metabolism and how they uphold the cell envelope,” Goley explains. “Uncovering the function of these enzymes is crucial since they represent potential drug targets.”
Other contributors to this research include co-first authors Allison Daitch and Erika Smith, both recent Ph.D. graduates from Goley’s lab at Johns Hopkins Medicine, and now part of the Biomedical Advanced Research and Development Authority at the U.S. Department of Health and Human Services and the National Institutes of Health, respectively.
The National Institute of General Medical Science (R35GM136221, T32GM007445) financed this research.
