Magnetotactic Bacteria: Magnetic Microbes
- Sylvia Rose
- Apr 4
- 4 min read
Magnetotactic bacteria (MTB) navigate their environment using magnetic fields. They're found in a variety of saline and freshwater environments, and have specialized organelles to synthesize magnetic minerals.
About Magnetotactic Bacteria
Magnetotactic bacteria are a diverse group of prokaryotic organisms. They lack a nucleus and other complex organelles. They can align and move along magnetic field lines, a phenomenon known as magnetotaxis.
Microbial magnetic navigation functions with magnetosomes, intracellular organelles containing magnetic crystals. In aquatic environments they move through sediment, soil and water.
In magnetotaxis the bacteria swim in the direction of magnetic fields. This helps them locate nutrient-rich areas and avoid harmful conditions. Oxygen molecules (O2) are paramagnetic, weakly attracted to magnetic fields.
Sulfur molecules are diamagnetic, meaning they'e weakly repelled by a magnetic field. Interaction of magnetic fields guides the bacterium in the desired direction.
MTB can live well in setting low in oxygen as well as aerobic conditions. With a slight shift in metabolism, they can become anaerobes.
Habitat
Sediments: They inhabit sediment layers of lakes, rivers, and oceans, especially in areas with low oxygen levels.
Water Columns: Some MTB species thrive in the water column, particularly in stratified water bodies with distinct oxygen gradients.
Salt Marshes and Estuaries: These habitats, with fluctuating salinity and oxygen levels, provide a desirable environment for many MTB.
They easily adapt to diverse ecological niches. In submerged wetlands, MTB are important to nutrient cycling. Extremophile MTB live in extreme locations, such as hydrothermal vents in the deep sea.
Extremophile magnetotactic bacteria are also found in hot springs. They're isolated from thermophilic sites in Nevada and Oregon.
Properties & Characteristics
Morphology: MTB come in various shapes, including spheres, rods, spirals, and more complex forms. Most are rod-shaped or spiral and range in size from 0.5 to 10 micrometers. There are 1000 micrometers in a millimeter.
Metabolism: Some are aerobic (requiring oxygen), while others are anaerobic (living without oxygen) and many are microaerophilic (preferring low oxygen levels). They use iron and sulfates as electron acceptors to live where oxygen is limited.
Magnetosomes: These organelles are species-specific in terms of size, shape, number, and arrangement of the magnetic crystals they contain.
Magnetosomes contain magnetic iron minerals like magnetite (Fe3O4) or greigite (Fe3S4). The magnetism in these bacteria originates here.
MTB synthesize magnetic minerals intracellularly in the magnetosomes. The bacteria uptake iron ions from their environment and convert them into magnetite or greigite crystals.
Magnetosome alignment in the bacteria enables them to quickly respond to magnetic fields. In Magnetospirillum gryphiswaldense, magnetosomes form long chains to improve the bacteria's orientation abilities.
Diet & Waste Products
MTB's dietary habits vary depending on the species and environment. Some are heterotrophic, consuming organic matter. They rely on compounds such as fatty acids, carbohydrates, and proteins.
Others are produce their own food through photosynthesis or chemosynthesis. Common waste products include carbon dioxide, sulfur compounds, and nitrogen compounds.
Excretions of magnetotactic bacteria facilitate sediment nutrient cycling. Their metabolic activities help break down toxic compounds, improving water quality in their habitats.
Formation of Magnetosomes
Formation process begins with the uptake of iron ions. Inside the bacteria, the ions crystallize into magnetic nanoparticles through biomineralization.
In biomineralization, biological processes of living organisms guide formation and deposition of mineral materials. This creates composite structures such as bones, teeth, shells, and other hard tissues.
The precise size and shape of magnetosomes are regulated to enhance magnetotactic behavior. Each little bacterium can have hundreds of magnetosomes.
Evolutionary Advantage of Magnetism
Magnetotaxis: By aligning with the Earth's magnetic field lines, MTB navigate towards their preferred microenvironments.
Oxygen Gradient Navigation: In stratified water bodies, MTB use magnetotaxis to find the transition zone between oxic (oxygen-rich) and anoxic (oxygen-deficient) layers. Thus they can access oxygen for respiration while avoiding toxicity of high oxygen levels.
Sediment Burial: In sediment environments, magnetotaxis can help MTB navigate towards deeper, more stable layers where they avoid disturbance from surface currents or wave action.
Binary Fission & Magnetism
MTB reproduce by binary fission. The magnetosomes are divided between the two daughter cells. This ensures both new cells inherit the ability to navigate using magnetic fields.
Distribution of magnetosomes may not always be equal, with some variation in magnetic strength between the offspring.
Facts About Magnetic Bacteria
Over 20 genera of magnetotactic bacteria have been identified, each with distinct morphological and metabolic traits.
Ecosystems: MTB are important in biogeochemical cycles, particularly in the cycling of carbon and iron. Their activities contribute to nutrient recycling and sediment formation, essential for healthy ecosystems.
Research: magnetosomes from MTB are explored for nanotechnology applications, such as drug delivery systems.
Sensory Adaptations: some MTB can also respond to gradients like chemicals and light.
Habitat Indicators: presence of these bacteria in ecosystems is an important indicator of environmental health, defining sediment quality and overall ecosystem stability.
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