New research shows how bacteria sense magnetic field polarity
A recent paper provides evidence for a direct link between two bacterial navigation mechanisms - one sensing magnetic field and the other oxygen concentration.
A bacterium with a chain of magnetosomes - magnetic dipoles orienting bacterium along the earth's magnetic field (Click to enlarge)
The collaborative work, between Professor Judy Armitage in the department and Dirk Schuler in Germany, is published in Nature Communications (1). The project saw graduate student Felix Popp from Dr Schuler's lab come to the department to use bacterial tracking software, developed in the Armitage lab, to analyse the swimming behaviour of populations of bacteria.
Aquatic environments are home to a diverse range of bacteria that carry chains of membrane bound magnetite-containing magnetosomes. The bacteria live at the aerobic/anaerobic interface and use the magnetosomes to orient along the earth's magnetic field and negative aerotaxis to move away from high oxygen.
Little is known about the motility and taxis of these bacteria and how they orient along the earth's magnetic field and show north- or south-seeking polarity. The behaviour may be integrated with other sensory responses or alternatively may use a dedicated sensing and signalling machinery.
The researchers found that when they grew magnetotatic bacteria in shake flasks, the bacteria kept the magnetosomes and orientation along the magnetic field but lost their north-south polarity. The polarity was only regained when the bacteria were placed in an environment with both an oxygen gradient and a magnetic field. It reformed in a direction dependent on the direction of the oxygen pulse.
The ability of the bacteria to repolarise the magnetosomes was lost in mutants deleted for the chemosensory pathway Che, which controls aerotactic behaviour - a finding which shows a direct connection between the sensory system controlling oxygen responses and signals from the inorganic magnetosome system.