Unlike the random motion M. xanthus exhibits at low levels of prey, the study shows that during predation, individual M. xanthus cells line up perpendicular to the axis of the ripple and move back and forth. This motion of individual cells, known as cell reversal produces an alternating pattern of high and low cell density like crests and troughs of waves, and the overall motion of the wave formation is directed toward prey.
The UI team also showed that the ripple wavelength is adaptable and dependent of how much prey is available. At high prey density, M. xanthus forms ripples with shorter wavelengths. As prey density decreases, the ripple wavelength gets longer. Eventually, when there is no more prey, the rippling behavior dissipates.
"The rippling appears to enhance predation by keeping more M. xanthus cells in the location of the prey cells," Kirby said.
Finally, the UI study found that the bacteria use a chemotaxis-like signaling pathway to regulate multi-cellular rippling during predation.
Individual M. xanthus cells move by shooting rope-like projections called pili from either end of the cell. These pili attach to surfaces allowing cells to pull themselves forward or backward in a "spiderman" type motion known as cell reversal. The genes that regulate this cell reversal process are chemotaxis-like genes.
The UI team mutated two genes in this pathway to study their effect on the predatory ability of the bacterium. One mutant strain rippled continuously even in the absence of prey, and individual cells exhibited a hyper-reversing action. Conversely, the second mutation produced bacteria that were not able to ripple at all.
Both mutants were unable to respond to change
|Contact: Jennifer Brown|
University of Iowa