The right place at the right time: new bacterium navigates using Earth’s magnetic field

ResearchBlogging.orgMTB Title ImageMany migratory birds have a mysterious ability to return home with remarkable accuracy, even from halfway around the world. Since the invention of the compass some 2,000 years ago, humans have been able to emulate this, albeit on a limited scale. But the discovery that even microbes can navigate in a similar manner is relatively recent. It was only in 1975 that Richard Blakemore, of the Woods Hole Oceanographic Institute in Massachusetts, described the first members of a small group of microbes we now know as magnetotactic bacteria (MTB). Their ability to sense the geomagnetic field and move accordingly is known as magnetotaxis.

Since 1975, a range of MTB have been discovered in several different branches of the tree of life. Besides magnetotaxis, the main thing they have in common is that they live in water and have flagella – whip-like appendages that they use to swim. Unlike birds and people, however, MTB do not use their inbuilt compass to move in a specific direction. In fact, they use magnetotaxis to avoid any north-south or east-west movement: MTB only move up or down within the body of water they live in. This is because they require very specific levels of oxygen concentration, which generally varies with water depth. Moving horizontally would quite simply be a waste of energy for these bacteria.

A group of scientists, led by Dr Yoshihiro Fukumori and Dr Azuma Taoka at Kanazawa University in Japan, have now isolated a particularly unusual MTB from a lake near the university. The novel bacterium does not yet have an official name as it has yet to be grown in a lab. However, the team have been able to get a close enough look to describe the microbe, which is temporarily called GRS-1, in considerable detail. Their findings are published in the journal Microbiology.

Too big to fit
Dr Zachery Oestreicher, a postdoc at Kanazawa University and a member of Dr Fukumori’s team, explains that GRS-1 is very different from all other known MTB. For example, the bacterium is so much bigger than any MTB ever seen before that the team were unsure at first if they were even dealing with a single-celled organism. GRS-1 also swims more slowly than other MTB, making it something of a slow, lumbering beast. This presented the scientists with some difficulties when trying to isolate the bacterium.

Figure 1: The newly discovered bacterium. The arrow points towards its flagella, which it uses to move

Figure 1: The newly discovered bacterium. The arrow points towards its bundle of flagella.

Normally, MTB are isolated using the so-called ‘racetrack method’ – a water sample is placed on a track with a cotton filter in the middle and a magnet at the end. Microbes can move through the cotton, but the MTB, attracted by the magnet, do so much faster than other organisms and are collected on the other side. This approach works because the magnetic field of a magnet at close range is far stronger than the Earth’s geomagnetic field.

However, GRS-1 is so large that it cannot fit in between cotton fibres, rendering the racetrack method infeasible. Instead, Junya Kondo, a former graduate student of Dr Fukumori’s, devised a simple but ingenious method to isolate GRS-1 from their water sample. He strapped a magnet to the side of the bottle containing the water sample and waited a few hours, giving the bacteria enough time to swim towards the magnet. The researchers then took a small sample from the water near the magnet, where the concentration of GRS-1 was now highest.

Repeating this process, the team achieved an even higher concentration of the bacteria in a water sample of just 0.25ml. This sample was small enough to view under a microscope, which they used to isolate individual GRS-1 bacteria using a very fine pipette.

Examining the inner compass
While scientists are still debating the mechanisms that birds use to find their way over vast distances, we have a much better idea of how microbial magnetotaxis works. MTB cells contain specialised structures called magnetosomes, which in turn contain magnetic crystals that act like a compass needle to orient the bacteria. In the case of GRS-1, the crystals consist of magnetite, the most magnetic naturally occurring mineral we know.

But even in the relatively well-understood area of magnetotaxis, GRS-1 presented the researchers with a riddle. Normally, magnetosomes are arranged along the longest axis of each MTB cell. In GRS-1, however, Kondo and his colleagues found that the magnetosomes were distributed in random clusters throughout the cells. It is not yet clear how exactly the movement of GRS-1 differs from that of other MTB as a result, and the team hope to address this question in future papers.

Transferable skills
Despite not being an official species yet, GRS-1 has been found to belong to the class Gammaproteobacteria. Only two other species of MTB have been discovered in this class so far, as recently as 2012 – and neither of these species bear much resemblance to GRS-1. Other known MTB species belong to the Alpha- and Deltaproteobacteria classes, and even to two different phyla (a higher taxonomic rank). How did a feature as specialised as magnetotaxis appear across unconnected branches in the tree of life?

This diagram shows the different daptations to flying in a pterosaur, a bat and a bird

Figure 2: This diagram shows the different adaptations to flying in a pterosaur, a bat and a bird.

The appearance of a trait in unrelated species is often due to a phenomenon called convergent evolution. This occurs when species from different lineages evolve similar solutions to the same problem. For example, birds and bats both fly, but their ability to do so evolved independently. The resulting mechanics of flight in the two groups are very different, as Figure 2 highlights.

However, convergent evolution is unlikely to have occurred in the case of magnetotaxis. Dr Oestreicher explains that the current model for the presence of MTB in different phyla and classes is horizontal gene transfer. During this process, sections of DNA are passed from one cell to another and ultimately become a part of that cell’s genome. The genes that encode the production of magnetosomes can move into a completely new genome particularly easily.

Even within a group of microbes as disparate as magnetotactic bacteria, the newly discovered GRS-1 is something of an outlier. It differs from other known MTB in a number of ways, and Dr Fukumori speculates that we have yet to discover many other ‘unusual’ MTB. He and his team look forward to playing their part in this undertaking, and in developing potential industrial or scientific applications for magnetotactic bacteria.

Jon Fuhrmann

Taoka, A., Kondo, J., Oestreicher, Z., & Fukumori, Y. (2014). Characterization of uncultured giant rod-shaped magnetotactic Gammaproteobacteria from a freshwater pond in Kanazawa, Japan Microbiology, 160 (Pt_10), 2226-2234 DOI: 10.1099/mic.0.078717-0

Image Credits:
Header Image: dayna mason on Flickr. Licensed under CC BY-NC-SA 2.0
Figure 1: Taoka et al. (2014)
Figure 2: TomCatX on wikimedia; modified after John Romanes (1892): From Darwin after Darwin
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UK Fungus Day 2014

Fungus Day12 October 2014 is UK Fungus Day, held by the British Mycological Society to showcase the diversity and usefulness of fungi, and the benefits of mycology (the study of fungi). Many people equate fungi with mushrooms, but mushrooms are only the visible, above-ground part of certain types of fungi. The bulk of such a fungus’s volume is underground and consists of microscopic threads called hyphae, which can form huge, interconnected networks. This means that mushrooms some distance apart may well belong to the same fungal organism.

Like plants and animals, fungi belong to the domain Eukaryota, which contains all organisms whose cells contain a nucleus. Unlike other eukaryotes, however, the cell walls of fungi contain chitin, a chemical structure also found in the hard shells of many insects and crustaceans.

Fungi are found around the world, with some 100,000 species currently known to mycologists. However, it is estimated that several million different species exist worldwide, so there is plenty of scope for discovery. Fungal species can grow in the most inhospitable regions, including deserts, deep ocean seafloors, and severely irradiated ground; some can even survive the intense ultraviolet and cosmic radiation in outer space, as findings aboard the International Space Station have shown.

Until just a few decades ago, fungi were thought to be closely related to plants: they both grow in similar habitats and do not move, and many fungi have similar above-ground shapes as flowering plants. Since the advent of molecular methods, however, we know that plants and fungi became genetically separate about a billion years ago. In fact, fungi are more closely related to animals than to plants! Continue reading

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New to Science – October Edition

ECleanroom at the Goddard Space Flight Center, Greenbelt, MD, USAach month, the Society for General Microbiology publishes the International Journal of Systematic and Evolutionary Microbiology, which details newly discovered species of bacteria, fungi and protists. Here are a few of the new species that have been discovered, and the places they’ve been found. The full papers are available to journal subscribers, but the abstracts are free to read.

The harvesting season is slowly coming to a close in large parts of the northern hemisphere – incidentally, the word ‘harvest’ itself originates in the Old English hærfest, meaning ‘autumn’. Microbiologists, too, have been busy in recent weeks, and as preparations begin for various harvest and thanksgiving celebrations around the world, we are introduced to some intriguing new agriculturally themed species in the latest edition of IJSEM.

Any idyllic notions you may hold about farm work are quickly dispelled when it comes to microbiology. An American team, for example, identified Peptoniphilus stercorisuis in a sample from a storage tank containing swine manure. The bacterium is the first known member of a new taxonomic family, the Peptoniphilaceae. Continue reading

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86th Anniversary of Fleming’s Discovery of Penicillin, the first antibiotic

photoPenicillin, the first widely available antibiotic drug, was discovered by Sir Alexander Fleming 86 years ago today, on 28 September 1928. Upon its introduction into mainstream medicine in the 1940s, penicillin was hailed as a ‘miracle cure’. To this day, antibiotics are widely used to treat or prevent infections.

“One sometimes finds what one is not looking for”

Sir Alexander Fleming

Fleming’s discovery was coincidental: his laboratory at St. Mary’s Hospital in London was notoriously messy, and he often left uncovered petri dishes containing bacteria that he no longer needed on his worktop. Upon returning from a holiday in Suffolk, he found that an old dish containing Staphylococcus aureus bacteria had been contaminated by a fungus, Penicillium notatum. Wherever the fungus grew, it was surrounded by bacteria-free zones where Staphylococcus could not grow. Upon further investigation, Fleming found that the ‘mould juice’ he derived from P. notatum effectively killed many kinds of bacteria. We went to the Fleming Museum in London to learn more about his work and how he made his famous discovery; you can listen the podcast we recorded here.

It was not until 1939 that three researchers at Oxford University turned penicillin from mould juice into a life-saving drug. Two years later, a devastating fire in the Cocoanut Grove nightclub in Boston became the first opportunity to test penicillin on a large scale: burn injuries and skin grafts are particularly susceptible to infection. Following the successful use of penicillin in the aftermath of the fire, the US government began to fund the mass production of the drug, which saved countless lives during World War II.

Fleming received his Knighthood in 1944 and a year later was jointly awarded the Nobel Prize for Medicine or Physiology, along with Howard Florey and Ernst Chain. In the same year, Sir Alexander became the first President of the Society for General Microbiology. Because the Nobel Prize can only be awarded to three people, Norman Heatley, the third Oxford pathologist instrumental in developing penicillin into a mass-produced, mainstream drug, missed out on the award. In 1990, partly to correct this oversight, he became the first non-medic to be awarded an honorary Doctorate of Medicine by Oxford University.

So how does this antibiotic actually work? Penicillin is a member of the β-lactam class of antibiotics and its chemical structure contains a ring of carbon and nitrogen that gives the class its name. Penicillin prevents bacteria from correctly building their cell wall, stopping them from dividing properly.

Antibiotic resistance was a problem even when penicillin was being developed. In fact, the first resistant bacterial strains were discovered before the drug was even available to the public. Alexander Fleming himself warned about the risks of antibiotic resistance in his Nobel Prize acceptance speech. Numerous derivatives and synthetic versions of penicillin have since been developed, and some of these, such as methicillin and amoxicillin, are widely used today.

Penicillin was the first of a great many antibiotics – over 100 have since been discovered. These drugs have saved innumerable lives, but there is a great need for new ones to be developed if we are to delay the threat of resistance and continue the legacy of Fleming, Florey, Chain and Heatley.

Jon Fuhrmann

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Microbe Talk: September 2014

William DallingerThe Reverend Dr William H Dallinger, is probably not a name you’re familiar with. However, he was an important figure in the history of early microbiology. We sent Ben to the Royal Society, to learn more about Dallinger’s life. Also this month, Ben spoke to Dr Jeanne Salje about her work on Scrub Typhus, a disease that is widespread in Southeast Asia.

Show notes:

If you’re accessing this page on your iPhone and can’t see the podcast player, you can subscribe to Microbe Talk on iTunes. You can also find us on Stitcher.

Benjamin Thompson

Image Credit: Wellcome Images Licensed under CC BY 4.0
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Thinking about science like Louis Pasteur: Lessons from History

ResearchBlogging.org3617385206_80c52b90e2_oScientific discoveries and achievements from centuries past are often portrayed as a set of fully-fledged concepts and perfect results. The exacting trial-and-error processes and frequent setbacks we know from modern-day science are rarely mentioned. Why could this be – was science ‘easier’ in the past?

Dr Keith Turner and Professor Marvin Whiteley of the University of Texas at Austin were intrigued by this phenomenon and looked at 19th century microbiology as a case study. To get a better insight into what really happened in laboratories a century and a half ago, they studied a paper by Louis Pasteur, one of the founding fathers of modern microbiology. Written in 1877, it is entitled Charbon et septicémie (Anthrax and septicaemia, an inflammatory response of the body to severe infections). The manuscript is written in Pasteur’s native French, so the researchers enlisted the help of Dr Turner’s wife, who translated the original text into English. Together, they have published their thoughts on Pasteur’s paper in the Journal of Medical Microbiology. Continue reading

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Unwelcome colonisers: biofilm formation on voice prostheses

ResearchBlogging.orgDiagram_showing_the_position_of_the_stoma_after_a_laryngectomy_CRUK_361.svgA human being’s voice is one of their most distinguishing and individual features. Most of us have experienced the frustration of temporarily losing our voices – but for many survivors of laryngeal cancer (cancer of the voice box), this loss is permanent. A laryngectomy, or full removal of the larynx, is a common last resort to treat this cancer if other options have failed. This operation disconnects the windpipe from the nose and mouth, leaving the patient to breathe through a hole in their neck called a stoma. The side effect of this operation, however, is that patients lose the ability to speak.

The challenge of giving these patients a voice has been partially solved; voice prostheses (VP) have been developed to allow people without larynges to speak again, albeit on a severely limited scale. A VP is a one-way valve that is placed into a puncture between esophagus and windpipe. If the stoma is covered, this valve allows air to escape through the esophagus and the mouth. With considerable training, people can then use this air to produce sounds in a variety of manners. An example of voice prosthesis speech can be heard in this video. Continue reading

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