Magnetic bacteria can align their movement with Earth’s magnetic field thanks to strings of magnetic nanoparticles inside their cells. The blueprints for making and linking these magnetosomes are stored in the genes of the bacteria.
An international research team led by Professors Dr. Dirk Schüler and Dr. René Uebe from the University of Bayreuth has for the first time discovered a group of such genes in non-magnetic bacteria. These genes are inactive but functional and probably entered the bacterium through horizontal gene transfer. The results of the research were presented in the ISME Journal.
The transfer of genes from one organism to another is called “horizontal” when it is not “vertical” inheritance as part of a propagation process. In the field of bacteria, the horizontal transmission of genetic information is an important source of modification of existing species or the appearance of new ones. The numerous genes that control the ability to synthesize magnetosomes can also be naturally transmitted horizontally to other bacteria.
However, until now, these genes have only been found in bacteria that already produce magnetosomes as a result of previous successful gene transfer. But now, the Bayreuth microbiologists and their research partners in Hungary and France have for the first time discovered a cluster of such genes in the genome of a non-magnetic bacterium. This is Rhodovastum atsumiense, which is classified as a photosynthetic bacterium because it can use energy from sunlight for its metabolism.
The magnetosome genes discovered in this bacterial species are inactive: cells could not be induced to form magnetosomes in the laboratory, even under a variety of different culture conditions. So far, no photosynthetic bacteria are known to be naturally magnetic, although Prof. Dr. Schüler’s team has previously succeeded in “magnetizing” such bacteria through artificial gene transfer.
“To our knowledge, this is the first detection of a complete set of ‘silent’ genes in a non-magnetic bacterium. This is probably an early evolutionary stage after the acquisition of the genes from another yet unknown bacterium. Further genome analyzes revealed that the transferred gene cluster likely originated from a magnetic bacterium belonging to the class Alphaproteobacteria. Future studies will show if these genes can be activated in the natural environment of the bacterium.
In any case, no activation occurs under laboratory conditions, as our results clearly show. Therefore, the presence of magnetosome genes alone does not indicate that magnetosome biosynthesis actually occurs. Therefore, caution is advised when interpreting corresponding genomic data found in public databases”, says Prof. Dr. Dirk Schüler, holder of the Chair for Microbiology at the University of Bayreuth.
The researchers also addressed the question of why the host bacterium Rhodovastum atsumiense did not delete the magnetosome genes, even though it did not gain any selection advantage from them during evolution. “The best way we can explain this, based on our analyzes of the genome, is this: gene transfer probably occurred at a more recent stage of evolution. Rapid knockdown was not necessary because the magnetosome genes do not have any deleterious effect on the host bacterium,” explains first author Dr. Marina Dziuba, a long-time research associate in the Microbiology research group at the University of Bayreuth.
The new research findings follow a study published two years ago. Here, the Bayreuth microbiologists succeeded in introducing the complete set of magnetosome genes from the magnetic bacterium Magnetospirillum gryphiswaldense, which has long been established as a model organism in research, into the genome of a non-magnetic bacterium. Soon after, these host bacteria began to biosynthesize magnetosomes. Apparently, they were able to express the acquired foreign genes.
The research at the University of Bayreuth was supported in part by the recently completed “SYNTOMAGX” project funded by the European Research Council, which aimed at the synthetic genetic “magnetization” of foreign organisms.
MV Dziuba et al.: Silent gene clusters encode magnetic organelle biosynthesis in a non-magnetotactic phototrophic bacterium. ISME Magazine (2022), DOI: https://doi.org/10.1038/s41396-022-01348-y
MV Dziuba et al.: Single-step transfer of biosynthetic operons endows a wetland non-magnetotactic Magnetospirillum strain with magnetosome biosynthesis. Environmental Microbe. (2020), DOI: https://dx.doi.org/10.1111/1462-2920.14950