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Ticks survive SEM imaging

03/26/2012
Ashley Yeager

For the first time, scientists have taken scanning electron microscope images of live ticks. The animals survived the high vacuum condition and beam of electrons used to take the images, suggesting that SEM could be used to see more clearly how ticks, mites and even living cells move.

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Dead cells are different from live ones, which is why scientists want to study organisms when they are still living. Now, a team of researchers has used a scanning electron microscope to take images and video footage of living ticks.

The ticks, Haemaphysalis flava, survived the high vacuum pressure and the beam of electrons used in a scanning electron microscope (SEM) to take high-resolution images. The results, which appear in PLoS One, show that scientists can use a scanning electron microscope to better visualize the structure and movement of living organisms (1).

Scientists have studied dead ticks using SEM since the 1970s. The high-resolution of the microscope gives researchers a better view of the organisms and allows them to identify new species and also analyze anti-parasitic drugs and how ticks attack their hosts.

A scanning electron microscope image of the tick H. flava while it is still alive.





But "everyone wants to know the morphological changes of living cells rather than dead ones," says Tsutomu Takegami of Kanazawa Medical University in Japan, who led the new study.

To see if that was possible, he and his collaborators put 20 living ticks into their scanning electron microscope, which focuses a beam of electrons through two condenser lenses and then onto the sample. The electron beam works at high vacuum pressure, about 1.5x10^-3 pascals.

Under these conditions, the scientists took images and video of each tick's body, legs, mouth and claws without having to dehydrate the samples or place an ionic liquid on them to act as a conductor for the electron beam. In the paper, the scientists suggest that the tick's body probably provides the electrical conductivity needed to make a clear SEM image.

The first experiment, however, did not show the scientists how the SEM affected the ticks. In another test, the scientists exposed one group of ticks to only the vacuum conditions, one to the vacuum and the electron beam, and one group to neither. Ticks not exposed to the electron beam survived two weeks, whereas half of the ticks exposed to the beam died within two days. The electron beam, but not the vacuum is lethal to ticks, Takegami says.

The scientists also found distortions in the images, which they thought were caused by the ticks' movement of their legs. Under normal conditions, ticks move their legs continuously. Under the vacuum pressure, the organisms moved their legs for several minutes, and then stopped. But once taken out of the microscope, they resumed walking. Based on this observation, the scientists think that the ticks stop moving and possibly even stop breathing to avoid damage to their system when in a hypoxic environment.

But the ticks could not avoid the SEM's beam of electrons, and the motion of their legs suggested that they could sense the electron beam as it scanned their bodies. The ticks would move their legs rapidly when the beam reached the edge of each appendage. The motion appeared in the SEM images as distortions, or blurs.

To confirm that the distortions were caused by leg motion of living ticks, the team took SEM images of dead ticks. Their legs shrunk and curled up beneath their bodies and did not show the same blurred pattern in the images. Takegami says the team needs to do more research to figure out what is causing the living ticks' reactions, but that they may have sensors at the tips of their legs that were sensitive to the beam.

He adds that the results show that ticks' real-time movements can now be captured as SEM images and video, but it's not clear whether SEM images can be taken of other living species. Other animals, however, can survive in a vacuum, so it may be possible, Takegami says, to use a scanning electron microscope to get a detailed look at them, and maybe even human cells, while they are still alive.

Reference:

1. Ishigaki Y, Nakamura Y, Oikawa Y, Yano Y, Kuwabata S, et al. 2012. Observation of Live Ticks (Haemaphysalis flava) by Scanning Electron Microscopy under High Vacuum Pressure. PLoS One 7(3): e32676.

Keywords:  Microscopy