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Getting the basics of bacteria growth
BLOOMINGTON, Ind.—In keeping with the belief “know thy enemy,” researchers at Indiana University (IU) and Harvard University are hoping to strike on new ways to combat antibiotic-resistant bacteria by starting at the beginning—by looking at how bacterial cell division occurs. Thanks to previous work out of scientists at IU, the team was able to view in detail what happens when bacteria cells divide, and their work appeared in Science in a study titled “Treadmilling by FtsZ filaments drives peptidoglycan synthesis and bacterial cell division.”
The team used multi-colored dyes known as fluorescent D-amino acids (FDAAs), which were developed in 2012 in the lab of Michael VanNieuwenhze, professor in the IU Bloomington College of Arts and Sciences’ Department of Chemistry. VanNieuwenhze is a coauthor on the study, and Yves Brun, the Clyde Culbertson Professor of Biology in the IU Bloomington College of Arts and Sciences’ Department of Biology, is also an author.
"This is the first time we’ve been able to observe cell division as a dynamic process—that is, a process occurring over time. This wasn’t possible before since we lacked the tools to see it," said Erkin Kuru, a former Ph.D. student in the labs of VanNieuwenhze and Brun and current research fellow at Harvard. Kuru led the creation of the dyes, and was also a coauthor on this most recent study.
Two cell parts that play a role in bacterial division are FtsA and FtsZ, cytoskeletal proteins. FtsZ is a tubulin homolog, as noted in the abstract of the Science paper, “a highly conserved cytoskeletal polymer that specifies the future site of division.” These proteins form skeleton-like fibers within cells to guide construction of the cell wall. In addition, enzymes known as penicillin-binding proteins, or PBPs, also serve to build cell walls. This trio coordinates to build cell walls in the middle of cells as they divide to ensure the cell contents don't evacuate.
Though the role of these three agents has been known for a while, this new work has shed light on how they interact, revealing that FtsZ serves as a kind of construction “foreman” that directs PBPs in building cell walls, according to Brun. It was also discovered that FtsZ, which is enshrouded by a biochemical chain known as a filament, is constantly losing a molecule at one end and gaining a molecule at the other. This circular motion around the edge of a cell is referred to as “treadmilling.”
IU researchers worked to chemically label cells for analysis, and Harvard scientists were responsible for undertaking the experiments that demonstrated the FtsZ and PBP proteins' activity inside the cell.
“We found that the division septum was built at discrete sites that moved around the division plane,” the authors noted in their abstract. “FtsAZ filaments treadmilled circumferentially around the division ring and drove the motions of the peptidoglycan-synthesizing enzymes. The FtsZ treadmilling rate controlled both the rate of peptidoglycan synthesis and cell division. Thus, FtsZ treadmilling guides the progressive insertion of new cell wall by building increasingly smaller concentric rings of peptidoglycan to divide the cell.” (Peptidoglycan is a mesh-like polymer, and it is what gives cell walls their shape and strength.)
IU researchers have been focused on bacteria for several years. The work on FDAAs was led by VanNieuwenhze and Brun, and the National Institutes of Health awarded them $3.3 million in February 2015 to form a unit with four other chemists and biologists from IU to improve on the method of visualizing and defining the peptidoglycan building process.
The team expected to use the second-generation FDAAs to enable imaging of peptidoglycan construction in Escherichia coli, Bacillus subtilis and Streptococcus pneumoniae, and the project was expected to run four years. Malcom Winkler, a professor in the IU Bloomington College of Arts and Sciences’ Department of Biology, will also be a principal investigator on this work. Specifically, the researchers will use the grant to develop new, better probes, test their hypotheses on how peptidoglycan is synthesized in ovoid bacteria (S. pneumoniae) and find genes responsible for controlling peptidoglycan dynamics in rod-shaped bacteria (E. coli and B. subtilis).
It's hoped that more—and more specific—knowledge about bacteria and how they reproduce will lead to options for more precise options in developing new antibiotics against resistant bacterial strains.
"This is the first study to 'connect the dots' between each part of the cell involved in bacterial cellular division," said Brun. "We've finally closed the circle on this mechanism and opened the door to more precise methods in the fight against antibiotic-resistant bacteria.”