Profiling Myxococcus xanthus Swarming Phenotypes through Mutation and Environmental Variation
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Myxococcus xanthus grows on surfaces as a predatory biofilm called a swarm. In nature, a feeding swarm expands by moving over and consuming prey bacteria.Keywords:
Myxococcus xanthus
Swarming (honey bee)
Swarming motility
Multicellular organism
Cooperation among individuals is necessary for evolutionary transitions to higher levels of biological organization. In such transitions, groups of individuals at one level (such as single cells) cooperate to form selective units at a higher level (such as multicellular organisms). Though the evolution of cooperation is difficult to observe directly in higher eukaryotes, microorganisms do offer such an opportunity. Here we report the evolution of novel cooperative behaviour in experimental lineages of the bacterium Myxococcus xanthus. Wild-type strains of M. xanthus exhibit socially dependent swarming across soft surfaces by a mechanism known as 'S-motility' that requires the presence of extracellular type IV pili. In lineages of M. xanthus unable to make pili, a new mechanistic basis for cooperative swarming evolved. Evolved swarming is mediated, at least in part, by enhanced production of an extracellular fibril matrix that binds cells-and their evolutionary interests-together. Though costly to individuals, fibril production greatly enhanced population expansion in groups of interconnected cells. These results show that fundamental transitions to primitive cooperation can readily occur in bacteria. PMID: 12955143
Myxococcus xanthus
Swarming (honey bee)
Multicellular organism
Swarming motility
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Myxococcus xanthus
Swarming (honey bee)
Multicellular organism
Swarming motility
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ABSTRACT The social soil-dwelling bacteria Myxococcus xanthus can form multicellular structures, known as fruiting bodies. Experiments in homogeneous environments have shown that this process is affected by the physico-chemical properties of the substrate, but they have largely neglected the role of complex topographies. We experimentally demonstrate that the topography alters single-cell motility and multicellular organization in M. xanthus. In topographies realized by randomly placing silica particles over agar plates, we observe that the cells’ interaction with particles drastically modifies the dynamics of cellular aggregation, leading to changes in the number, size and shape of the fruiting bodies, and even to arresting their formation in certain conditions. We further explore this type of cell-particle interaction in a minimal computational model. These results provide fundamental insights into how the environment topography influences the emergence of complex multicellular structures from single cells, which is a fundamental problem of biological, ecological and medical relevance.
Myxococcus xanthus
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Abstract Myxococcus xanthus is a bacterium that lives on surfaces as a predatory biofilm called a swarm.As a growing swarm feeds on prey and expands, it displays dynamic multicellular patterns such as traveling waves called ripples and branching protrusions called flares. The rate at which a swarm expands across a surface, and the emergence of the coexisting patterns, are all controlled through coordinated cell movement. M. xanthus cells move using two motility systems known as Adventurous (A) and Social (S). Both are involved in swarm expansion and pattern formation. In this study, we describe a set of M. xanthus swarming genotype-to-phenotype associations that include both genetic and environmental perturbations. We identified new features of the swarming phenotype; recorded and measured swarm expansion using time-lapse microscopy; and compared the impact of mutation on different surfaces. These observations and analyses have increased our ability to discriminate between swarming phenotypes and provided context that allowed us to identify some phenotypes as improbable ‘outliers’ within the M. xanthus swarming phenome. Importance Myxococcus xanthus grows on surfaces as a predatory biofilm called a swarm. A feeding swarm expands by moving over and consuming prey bacteria. In the laboratory, a swarm is created by spotting cell suspension onto nutrient agar in lieu of prey. The cells quickly settle on the surface and the new swarm then expands radially. An assay that measures the expansion rate of a swarm of mutant cells is the first, and sometimes only, measurement used to decide whether a particular mutation impacts swarm motility. We have broadened the scope of this assay by increasing the accuracy of measurements and reintroducing prey, resulting in new identifiable and quantifiable features that can be used to improve genotype-to-phenotype associations.
Myxococcus xanthus
Swarming (honey bee)
Swarming motility
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ABSTRACT Pseudomonas aeruginosa is capable of twitching, swimming, and swarming motility. The latter form of translocation occurs on semisolid surfaces, requires functional flagella and biosurfactant production, and results in complex motility patterns. From the point of inoculation, bacteria migrate as defined groups, referred to as tendrils, moving in a coordinated manner capable of sensing and responding to other groups of cells. We were able to show that P. aeruginosa produces extracellular factors capable of modulating tendril movement, and genetic analysis revealed that modulation of these movements was dependent on rhamnolipid biosynthesis. An rhlB mutant (deficient in mono- and dirhamnolipid production) and an rhlC mutant (deficient in dirhamnolipid production) exhibited altered swarming patterns characterized by irregularly shaped tendrils. In addition, agar supplemented with rhamnolipid-containing spent supernatant inhibited wild-type (WT) swarming, whereas agar supplemented with spent supernatant from mutants that do not make rhamnolipids had no effect on WT P. aeruginosa swarming. Addition of purified rhamnolipids to swarming medium also inhibited swarming motility of the WT strain. We also show that a sadB mutant does not sense and/or respond to other groups of swarming cells and this mutant was capable of swarming on media supplemented with rhamnolipid-containing spent supernatant or purified rhamnolipids. The abilities to produce and respond to rhamnolipids in the context of group behavior are discussed.
Swarming (honey bee)
Swarming motility
Tendril
Rhamnolipid
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Myxococcus xanthus
Multicellular organism
Gliding motility
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Myxococcus xanthus
Multicellular organism
Gliding motility
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Myxococcus xanthus grows on surfaces as a predatory biofilm called a swarm. In nature, a feeding swarm expands by moving over and consuming prey bacteria.
Myxococcus xanthus
Swarming (honey bee)
Swarming motility
Multicellular organism
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Citations (2)
Bacterial swarming involves the differentiation of vegetative cells into hyperflagellated swarm cells which undergo cycles of rapid and coordinated population migration across solid surfaces. Species capable of this simple form of developmental behaviour lie on the boundary between unicellular and multicellular organisms and provide processes for study which are not only of intrinsic interest but which are analogous to components of more complex eukaryotic systems. This review attempts to place current knowledge of bacterial swarming within the framework provided by more extensively studied forms of prokaryotic multicellular behaviour. It discusses the potential of swarming as a readily accessible model of differentiation and multicellular behaviour and describes evidence indicating that swarming differentiation plays an important role in bacterial virulence.
Swarming (honey bee)
Multicellular organism
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Myxococcus xanthus
Multicellular organism
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