Could Social Networks Enable Stealthy Bacterial Communication?

M. xanthus cells are connected by an arrangement of chain-like membranes, made up of spherical organelles called vesicles. Scientists initially thought vesicles drifted around randomly until they were encountered by another M. xanthus cell. However, Manfred Auer and colleagues at Berkeley Lab’s Life Sciences Division found that vesicles have a much more targeted way of keeping in touch: the bacteria send out chains of vesicles, and some cells also send out tubes made of vesicles. The never before seen chains and tubes connect every cell to many other cells, creating a microscopic intranet.

These research findings are published in the journal Environmental Biology. The scientists collect data with a Zeiss Focused Ion Beam Scanning Electron Microscope (FIB/SEM). Using the back-scattered electrons of the SEM at relatively low voltage, they image the surface of a resin block containing an embedded, flash-frozen sample of M. xanthus. They then use the ion beam to mill away five nanometer slices of the surface of the resin block. This process repeats hundreds or thousands of times, depending on how large a volume the scientists want to examine.

“As volumes from this techniques are getting larger – most recently terabytes, we will need to employ supercomputing facilities, such as provided by NERSC (US National Energy Research Scientific Computing Center),” says Auer. “Together, NERSC and the Computational Research Division at LBNL (Lawrence Berkeley National Lab) are developing web-based visualization and analysis capabilities for such large 3D data sets. The ultimate goal is to make these resources accessible to a worldwide audience.”

The scientists believe M. xanthus uses its social network to transfer proteins and other molecules back and forth. This could enable the bacteria to coordinate activities, like evading bacterial enemies or snaring prey, without revealing its location. “The network could be a mode of stealth communication,” Auer notes. In turn, the team found that vesicle chains contain two proteins known to be transferrable from cell to cell when cells are touching. They think these proteins travel through the chains as cargo carriers.

Recent discoveries, such as vesicle chain fractions’ ability to kill E. coli,have inspired the team to study how the vesicle chain’s composition changes when M. xanthus interacts with foe versus food. Findings could shed light on how other bacteria work together to pull off important processes, such as breaking down plant material for biofuel production or cleaning up underground toxins. Perhaps more importantly, this research as a whole could lead to new antibiotics that stop harmful bacteria by knocking out their communication systems. -- © i SGTW