10:45 AM - 12:15 PM
[SEM15-P13] Increase of magnetite synthesizing population of Magnetospirillum magnetotacticum MS-1 by magnetic separation and subculture
Keywords:paleomagnetism, Magnetotactic bacteria
Magnetospirillum magnetotacticum MS-1 is a microaerophilic, magnetotactic bacterium that synthesizes a linear array of magnetite particles and can be cultured in the laboratory. However, when cultured in the laboratory, populations that do not synthesize magnetite tend to predominate. For example, to study the quantitative importance of MS-1 populations to the remanent magnetization acquired by sediments, many magnetite-synthesizing populations would be required, which would require many long-term, large-volume MS-1 culture cycles.
In this study, to increase the proportion of magnetite-synthesizing populations in MS-1, we applied magnetic separation to selectively pass on magnetite-synthesizing populations in "magnetic separation passaging". In this study, a total of 10 magnetic separation and passages were conducted from the 0th generation to the 10th generation. To ensure enough individuals for magnetic measurements, mass culture was conducted based on small-volume cultures of generations 2, 4, 6, 8, and 10, respectively, and a concentrated suspension of MS-1 was prepared. The magnetic moment increased up to the fourth generation but decreased thereafter. The total number of MS-1 individuals was also counted under a fluorescence microscope, and the total number of individuals increased up to the fourth generation, but then began to decrease. Therefore, the proportion of magnetite-synthesizing individuals increased up to the fourth magnetic separation. Furthermore, transmission electron microscopy (TEM) of the 6th and 10th generations revealed that the proportion of magnetite-synthesizing individuals was 3% in the 6th generation and 1% in the 10th generation, but the number of magnetite synthesized per individual was approximately 30 in the 6th generation and 50 in the 10th generation.
The following factors may explain why the magnetic moment and the total number of individuals reached a maximum in the middle of repeated cycles of magnetic separation and passaging. The laboratory culture is thought to have produced two types of cells: a "non-magnet type" that does not synthesize magnetite but grows rapidly, and a "magnet type" that synthesizes magnetite but grows slowly. As a result of repeated magnetic separation, the latter type gradually became dominant and its properties were strengthened, resulting in an increase in the number of intracellular magnetite while the total number of individuals after culture decreased, but the balance of these trends is thought to have reached a maximum in the fourth generation.
Therefore, we conclude that the largest MS-1 magnetite synthesizing population was obtained in the fourth generation of magnetic separation successional culture.
In this study, to increase the proportion of magnetite-synthesizing populations in MS-1, we applied magnetic separation to selectively pass on magnetite-synthesizing populations in "magnetic separation passaging". In this study, a total of 10 magnetic separation and passages were conducted from the 0th generation to the 10th generation. To ensure enough individuals for magnetic measurements, mass culture was conducted based on small-volume cultures of generations 2, 4, 6, 8, and 10, respectively, and a concentrated suspension of MS-1 was prepared. The magnetic moment increased up to the fourth generation but decreased thereafter. The total number of MS-1 individuals was also counted under a fluorescence microscope, and the total number of individuals increased up to the fourth generation, but then began to decrease. Therefore, the proportion of magnetite-synthesizing individuals increased up to the fourth magnetic separation. Furthermore, transmission electron microscopy (TEM) of the 6th and 10th generations revealed that the proportion of magnetite-synthesizing individuals was 3% in the 6th generation and 1% in the 10th generation, but the number of magnetite synthesized per individual was approximately 30 in the 6th generation and 50 in the 10th generation.
The following factors may explain why the magnetic moment and the total number of individuals reached a maximum in the middle of repeated cycles of magnetic separation and passaging. The laboratory culture is thought to have produced two types of cells: a "non-magnet type" that does not synthesize magnetite but grows rapidly, and a "magnet type" that synthesizes magnetite but grows slowly. As a result of repeated magnetic separation, the latter type gradually became dominant and its properties were strengthened, resulting in an increase in the number of intracellular magnetite while the total number of individuals after culture decreased, but the balance of these trends is thought to have reached a maximum in the fourth generation.
Therefore, we conclude that the largest MS-1 magnetite synthesizing population was obtained in the fourth generation of magnetic separation successional culture.