Transmission of a signal that synchronizes cell movements in swarms of Myxococcus xanthus

Abstract

We offer evidence for a signal that synchronizes the behavior of hundreds of Myxococcus xanthus cells in a growing swarm. Swarms are driven to expand by the periodic reversing of direction by members. By using time-lapse photomicroscopy, two organized multicellular elements of the swarm were analyzed: single-layered, rectangular rafts and round, multilayered mounds. Rafts of hundreds of cells with their long axes aligned in parallel enlarge as individual cells from the neighborhood join them from either side. Rafts can also add a second layer piece by piece. By repeating layer additions to a raft and rounding each layer, a regular multilayered mound can be formed. About an hour after a five-layered mound had formed, all of the cells from its top layer descended to the periphery of the fourth layer, both rapidly and synchronously. Following the first synchronized descent and spaced at constant time intervals, a new fifth layer was (re)constructed from fourthlayer cells, in very close proximity to its old position and with a number of cells similar to that before the "explosive" descent. This unexpected series of changes in mound structure can be explained by the spread of a signal that synchronizes the reversals of large groups of individual cells.timer | pattern formation | cell polarity | synchrony | polysaccharide

A Genetic Screen in Myxococcus xanthus Identifies Mutants That Uncouple Outer Membrane Exchange from a Downstream Cellular Response

“…We hypothesize that the introduction of nonmotile cells within a motile population breaks the harmony of the population and leads to swarm dysfunction. Consistent with this view, Kaiser and Warrick have recently demonstrated that the movement of cells within a swarm shows a surprisingly high degree of synchronization (37). We suggest that this synchronization is disrupted when nonmotile cells are mixed in the population.…”

The cognitive cell: bacterial behavior reconsidered

“…In contrast, consider the delta-proteobacterium M. xanthus , a social predator that inhabits soil, arguably one of the most complex ecosystems on the planet. Potentially the primate of the eubacteria, M. xanthus is renowned for its myriad collective behaviors, including structured, multidimensional swarming motility ( Kaiser and Warrick, 2014 ), pack-like predation ( Berleman and Kirby, 2009 ), and the use of chemical cues to lure faster-moving prey ( Shi and Zusman, 1993 ), as well as a complex developmental sequence leading to fruiting body formation and sporulation. At 9.14 Mbp, the M. xanthus genome is one of the top 20 in size and expresses 687 ST systems, of which more than half (54%, N = 372) are 2CSs.…”

“…Nevertheless, a stream of recent research into swarming motility in M. xanthus ( Mignot et al, 2005 , 2007 ; Nudleman et al, 2005 ; Mauriello et al, 2009b ; Nan et al, 2010 ; Kaiser and Warrick, 2011 , 2014 ; Pathak et al, 2012 ) has thrown light on very different processes of motility that involve vastly more components and produce much more observable behavior than flagellar rotation mediated by Che proteins.…”

“…Myxococcal swarming displays compelling similarities to flocking in birds, shoaling in fish and swarming in insects, the mechanisms of which have yet to be resolved in these animals ( Wu et al, 2009 ). Other features appear to have mechanistic and functional similarities to critical signaling pathways involved in development in animals, notably, Wnt and Hedgehog ( Kaiser and Warrick, 2014 ). Yet another feature—‘resetting’ a cytoplasmic pacemaker that regulates periodic reversal in cell direction ( Kaiser and Warrick, 2014 )—appears (to this writer) to bear a functional resemblance to synaptic scaling in neurons, a process critical to memory and learning in animals with nervous systems ( Turrigiano, 2008 ).…”

How Myxobacteria Cooperate

“…FrzCD protein clusters transiently realign between adjacent cells upon side-by-side contact to trigger cell reversals [38]. These interactions between side-by-side cells may help the population to coordinate and synchronize cell movements [39]. Thus, M. xanthus uses a variety of cell-cell interactions to organize the macro-scale movement of the swarm unit.…”