“2019 Microbe of the Year”: Bayreuth microbiologists discover key protein for cell division in magnetic bacteria
University of Bayreuth, Press release No. 026/2019, 12 March 2019
Magnetotactic bacteria have the fascinating ability to navigate within the Earth’s magnetic field. In the scientific journal mBio, researchers from the University of Bayreuth, LMU and the Max-Planck-Institute for Biochemistry in Munich, report on new findings about the “2019 Microbe of the Year”, the bacterium Magnetospirillum gryphiswaldense, which lives on the bottom of fresh water habitats. Electron micrographs prove that coordinated cell division in this microbe depends crucially on the protein “PopZ”. The study has provided valuable insights for basic research into microbiology in general, but especially into the division and internal organisation of bacterial cells.
Dr. Daniel Pfeiffer (right), co-author of the new study, with Bayreuth bachelor’s degree students Julian Herz and Annika Stüven (from left), who also contributed to the research work. Photo: Christian Wißler.
Like most magnetotactic bacteria, Magnetospirillum gryphiswaldense is a unicellular organism which reproduces through cell division. This process requires that the genetic material, but also its organelles, such the magnetosomes are evenly distributed between the two daughter cells. Only in this way is it possible for both daughter cells to develop into a fully functioning bacterial cell.
As the scientists found out, the protein PopZ is crucially important in cell division proceeding error free. The PopZ molecules are found in high concentration at the ends of the screw-shaped bacterial cell. These protein clusters function as docking stations for numerous other proteins necessary for cell division. In cells, in which the gene encoding PopZ was eliminated, not only motility is reduced, but also cell division is impaired to the extent that the daughter cells are not equally supplied with the material necessary for proper cellular development. Hence, both extremely long as well as tiny mini-cells result. When, on the other hand, the bacterial cells produce too much PopZ, other anomalies arise: Thin extensions, in which excess PopZ collects, form. Consequently, these extensions appear considerably brighter than the rest of the bacterial cell under the electron microscope.
Magnetospirillum gryphiswaldense cells lacking the protein PopZ are unusually elongated. The magnetosomes are visible inside the bacteria. Electron microscopic image: Daniel Pfeiffer, University of Bayreuth.
Moreover, the use of high-resolution fluorescence microscopy revealed a further striking feature. Magnetospirillum gryphiswaldense differs from all other known investigated bacteria with regard to the timing with which accumulations of the protein PopZ develop. Already in the final stage of cell division or very shortly afterwards, new clusters of this protein arise at the new poles of the daughter cells.
“Our findings are of great interest for a deeper understanding of intracellular organisation in general, and of cell division in bacteria”, explains Dr. Daniel Pfeiffer, first author of the new study. Prof. Dr. Dirk Schüler, one of the world’s leading experts in the area of magnetotactic bacteria, adds: “We have already known for a while that the protein PopZ is present in many magnetic bacteria, but also in many of its non-magnetic relatives. But now, the functions of this protein for a magnetotactic bacteria have been precisely determined for the first time. During this study we greatly took advantage of by the so-called ‘structured illumination microscopy’. This is a new method of super-resolution fluorescence microscopy, for which we on the Bayreuth Campus have been superbly equipped since just recently.”
When there is excessive production of the protein PopZ, long, thin extensions develop, which appear conspicuously bright in the electron microscopic. Photo: Daniel Pfeiffer, University of Bayreuth.
Since 2014 the Association for General and Applied Microbiology (VAAM) has selected one microorganism as „Microbe of the Year“. What is decisive in their choice is the significance of the respective microorganism, for example with respect to ecology, medicine, food industry, energy production but also more generally to scientific research. For 2019, the honour went to Magnetospirillum gryphiswaldense. This microbe was discovered by the Dirk Schüler in the 1980s, when he isolated it from the mud of a river while still being a diploma student. Today it has become an important model bacterium at the University of Bayreuth, where Schüler is leader of the Chair for Microbiology. Here and in many other laboratories around the world, it serves as a model organism for research into the cell biology of bacteria, and their orientation within magnetic fields by the help of magnetosomes. These are tiny particles, only a few nanometres in size, present inside Magnetotactic bacteria. They line up like beads on a string, and react much like the needle of a compass to the Earth’s magnetic field. “Once we achieve a detailed understanding of the biosynthesis of magnetosomes, and optimize it in the laboratory, we will have some exciting possibilities to create magnetic nanomaterials with new, tailor-made characteristics” says Schüler.
Interview with Prof. Dr. Dirk Schüler on the “2019 Microbe of the Year”:
Daniel Pfeiffer, Mauricio Toro-Nahuelpan, Marc Bramkamp, Jürgen Plitzko, and Dirk Schüler: The polar organizing protein PopZ is fundamental for proper cell division and segregation of cellular content in Magnetospirillum gryphiswaldense.
mBio (2019), DOI: 10.1128/mBio.02716-18
The research has been funded by the Deutsche Forschungsgemeinschaft (DFG) and the European Research Council (ERC).
Prof Dr. Dirk Schüler
Chair for Microbiology, University of Bayreuth
Phone: +49 (0)921 / 55-2729
Dr. Daniel Pfeiffer
Microbiology, University of Bayreuth
Phone: +49 (0)921 / 55-2595
University of Bayreuth
Universitätsstr. 30 / ZUV
Phone: +49 (0)921 / 55-5356