Abstract
We controlled and observed individual magneto-tactic bacteria (Magnetospirillum gryphiswaldense) inside a 5, upmu hbox {m}-high microfluidic channel for over 4 h. After a period of constant velocity, the duration of which varied between bacteria, all observed bacteria showed a gradual decrease in their velocity of about 25, hbox {nm}/hbox {s}^2. After coming to a full stop, different behaviour was observed, ranging from rotation around the centre of mass synchronous with the direction of the external magnetic field, to being completely immobile. Our results suggest that the influence of the high-intensity illumination and the presence of the channel walls are important parameters to consider when performing observations of such long duration.
Highlights
Long-term microscopic observation can help us to understand bacteria behaviour, such as cell division (Inoue et al 2001) or transition into a growth-arrest phase (Gefen et al 2014)
One Magneto-tactic bacteria (MTB) was tracked at a time
When the selected MTB stopped moving, the magnetic field was directed to be parallel to the microfluidic channel in order to find and trap a new MTB
Summary
Long-term microscopic observation can help us to understand bacteria behaviour, such as cell division (Inoue et al 2001) or transition into a growth-arrest phase (Gefen et al 2014). These experiments are most performed on nonmotile bacteria. Long-term observation of motile bacteria is far more difficult, but interesting. Do they always swim, during cell division?. When we want to observe motile rather than fixed bacteria in an optical microscope, there are two additional issues: Communicated by Erko Stackebrandt.
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