Magnetospirillum gryphiswaldense

This student page has not been curated.

Classification

Domain: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rhodospirillales
Family: Rhodospirillaceae

Species

NCBI: [1]

Magnetospirillum gryphiswaldense

Description and Significance

Describe the appearance, habitat, etc. of the organism, and why you think it is important.

Genome Structure

The complete genome of M. gryphiswaldense was first sequenced in 2014 by Wang X. et. al. using Illumina Solexa and Roche 454 reads [9]. This initial read identified a single circular chromosome with 4,261 coding sequences [9]. A more accurate genome sequencing was performed in 2018 by René Uebe et. al., which again identified a single circular contig consisting of 4,155,740 bp with a G+C content of 63.3% [4,9]. The M. gryphiswaldense genome consists of 3,980 genes, and also contains 88 transposons. This high number of transposons explains why the M. gryphiswaldense genome is so highly flexible and could account for the differences seen between the 2014 and 2018 genome reads [9].

Complete 'M. gryphiswaldense' Genome Sequence: [2]

The Magnetosome Island (MAI)

The ‘Magnetosome Island’ (MAI) is a region of the M. gryphiswaldense genome that is of particular interest because it contains all the genes necessary for magnetosome formation, magnetite crystal growth, and magnetotaxis [1,11]. The genomic region is about 130 kb in size and contains three important classes of genes:

1. mam (magnetosome membrane) genes
2. mms (magnetosome membrane specific) genes
3. mtx (magnetotaxis) genes

All of these MAI genes are controlled by 4 main operons: mamAB, mamGFDC, mms6, and mamXY [1]. Deletion experiments preformed on the M. gryphiswaldense strain MRS-1 suggest that the only genes that are essential for nanomagnet synthesis are those controlled by the mamAB operon [1]. These mamAB-controlled genes contribute to formation of the magnetosome membrane, formation of the magnetite crystal, maturation of the magnetite crystal, and alignment of the magnetosome chain [1]. A study by Wang Q. et. al. revealed the MAI also contains 80 differentially expressed genes (DEGs) (53 upregulated and 27 downregulated), which vary in response to iron concentrations [11].

Evolution of MTBs

There are multiple theories for the evolution of magnetoactive bacteria based on their genetic makeup. Some say that the high conservation of the mam genes suggests a monophyletic origin, where all MTBs shared one common ancestor [1]. However, the rich diversity seen among MTBs could suggest that their evolution stemmed from multiple different lineages, and that the conservation of specific genes was due to a large amount of horizontal gene transfer, rather than a single common ancestor [1].

Cell Structure and Nanomagnet Synthesis

Cell Structure

As previously mentioned, M. gryphiswaldense are spirilla, or helically shaped single-celled microbes with rotating flagella at either end of their bodies [1,6]. Their cell walls are gram-negative, meaning that they lack a thick peptidoglycan layer [5]. M. gryphiswaldense are usually several micrometers long and have a diameter of about half a micrometer [13]. The magnetic moment of M. gryphiswaldense as measured by light scattering was found to be 2.53± 1.6×10^16〖Am〗^2 [1].

While there is not much literature on the reproduction of M. gryphiswaldense research has shown that the turn-around time from initial reproduction to a fully-functioning organism (producing nanomagnets) is about 24 hours under ideal conditions (iron and oxygen conditions) [2].

Nanomagnet Synthesis

M. gryphiswaldense synthesizes nanomagnets made of an iron oxide know as magnetite (Fe3O4), which is the most magnetic naturally occurring mineral on earth [1]. The magnetite nanomagnets are formed through the process of biologically controlled mineralization (BCM), where M. gryphiswaldense creates an organic mold, pulls in iron ions from the environment, and then oxidizes those ions so that they crystalize as magnetite [1]. The nanomagnets themselves are cuboctahedral in shape, and about 40-45 nm in size [11].

In M. gryphiswaldense, BCM occurs within the magnetosomes: organelles that each consist of a phospholipid and fatty acid membrane surrounding a growing nanomagnet [8]. These magnetosome vesicles the result of cytoplasmic membrane invagination, which occurs before magnetic crystal growth begins [1,11]. Once the magnetosome membrane has separated from the cytoplasmic membrane, its fatty acid and phospholipid proportions are slightly adjusted [8]. At least 18 specific proteins can be found within the magnetosome membrane as well, having attached to the magnetosome membrane either before or after membrane invagination [8]. M. gryphiswaldense arranges these magnetosomes in a linear configuration, held in place by cytoskeletal filaments [1].

Ecology

M. gryphiswaldense can be found in freshwater, aquatic environments where there is vertical chemical stratification (i.e., varying concentrations of oxygen and iron ions within the water) [1]. Specifically, M. gryphiswaldense is highly sensitive to oxygen concentrations; being microaerophilic, they prefer only very low levels of dissolved oxygen (around 0.5-1.0%) [1,6]. M. gryphiswaldense remains at an ideally oxygenated level within its environment through magnetotaxis [1]. The chain of magnetosomes within M. gryphiswaldense allows the microbe to be continually aligned with the geomagnetic field, providing a sense of direction [1]. If oxygen levels are too low, M. gryphiswaldense simply propels itself upwards in line with the geomagnetic field until it reaches an ideal oxygen concentration [1]. Likewise, if oxygen levels become too high, the microbe simple reverses its direction of flagella rotation, and swims down along the geomagnetic field lines until it reaches lower oxygen levels [1]. By limiting movement to a fixed axis that aligns with the oxygen gradient, M. gryphiswaldense is able to efficiently explore an maneuver within its environment.

Applications

M. gryphiswaldense is potentially a highly lucrative microbe in terms of biotechnology applications because it synthesizes strong nanomagnets with high precision; synthetic nanomagnet production is not nearly as precise or dependable [3]. Magnetosomes can serve a wide range of different purposes because they are very small but can also be easily separated from mixtures because they are magnetic [3]. Additionally, the surface properties of the magnetosome membrane make it relatively simple to attach amounts of specific molecules to the magnetosome surface [10]. Some specific applications for both entire MTBs (including M. gryphiswaldense) and magnetosomes alone are listed below [10].

Magnetoactive Bacteria Applications

• Drug Delivery
• Bioremediation
• Energy Generation
  

Magnetosome Applications

• Drug Delivery
• Cell Separation
• Food Safety
• DNA and Antigen Recovery or Detection
• MRA Contrast Agent
• Hyperthermia
• Enzyme immobilization
  

References

[1] Abreu, F., & Acosta-Avalos, D. (2018). Biology and Physics of Magnetotactic Bacteria. Microorganisms.

[2] Ardelean, I., Moisescu, C., Ignat, M., Constantin, M., & Virgolici, M. (2009). Magnetospirillum Gryphiswaldense:Fundamentals and Applications. Biotechnology & Biotechnological Equipment, 23(sup1), 751–754.

[3] Green, H., Hofmeister, C., Chin, S., & Coyte, E. (2016). The Bacteria That Make Perfect, Tiny Magnets. YouTube. SciShow.

[4] Magnetospirillum gryphiswaldense (ID 1508). (2014).

[5] Mannucci, S., Ghin, L., Conti, G., Tambalo, S., Lascialfari, A., Orlando, T., … Sbarbati, A. (2014). Magnetic Nanoparticles from Magnetospirillum gryphiswaldense Increase the Efficacy of Thermotherapy in a Model of Colon Carcinoma. PLoS ONE, 9(10).

[6] [https://doi.org/10.1007/s007060200047 Šafařík, I., & Šafaříkov&#, M. (2002). Magnetic Nanoparticles and Biosciences. Monatshefte f�r Chemie / Chemical Monthly, 133(6), 737–759.]

[7] Schüler, D., & Köhler, M. (1992). The isolation of a new magnetic spirillum. Zentralblatt Für Mikrobiologie, 147(1-2), 150–151.

[8] Sun, J., Li, Y., Liang, X.-J., & Wang, P. C. (2011). Bacterial Magnetosome: A Novel Biogenetic Magnetic Targeted Drug Carrier with Potential Multifunctions. Journal of Nanomaterials, 2011, 1–13.

[9] Uebe, R., Schüler, D., Jogler, C., & Wiegand, S. (2018). Reevaluation of the Complete Genome Sequence of Magnetospirillum gryphiswaldense MSR-1 with Single-Molecule Real-Time Sequencing Data. Genome Announcements, 6(17).

[10] Vargas, G., Cypriano, J., Correa, T., Leão, P., Bazylinski, D., & Abreu, F. (2018). Applications of Magnetotactic Bacteria, Magnetosomes and Magnetosome Crystals in Biotechnology and Nanotechnology: Mini-Review. Molecules, 23(10), 2438.

[11] Wang, Q., Wang, X., Zhang, W., Li, X., Zhou, Y., Li, D., … Li, J. (2017). Physiological characteristics of Magnetospirillum gryphiswaldense MSR-1 that control cell growth under high-iron and low-oxygen conditions. Scientific Reports, 7(1).

[12] Wang, X., Wang, Q., Zhang, W., Wang, Y., Li, L., Wen, T., … Li, J. (2014). Complete Genome Sequence of Magnetospirillum gryphiswaldense MSR-1. Genome Announcements, 2(2).

[13] Zahn, C., Keller, S., Toro-Nahuelpan, M., Dorscht, P., Gross, W., Laumann, M., … Kress, H. (2017). Measurement of the magnetic moment of single Magnetospirillum gryphiswaldense cells by magnetic tweezers. Scientific Reports, 7(1).

Author

Page authored by MacKenzie Emch, student of Prof. Jay Lennon at IndianaUniversity.