The mechanics of gravitaxis in<i>Paramecium</i>

Roberts, A. M.

doi:10.1242/jeb.050666

Cited by 31 publications

(41 citation statements)

References 21 publications

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“…they swim downwards. This is in contrast to most other genera (Hemmersbach et al, 1998), such as Bursaria (Krause & Bräucker, 2009), Didinium (Bräucker et al, 1994), Paramecium (Bräucker et al, 1994;Roberts, 2010;Machemer, 2014), Stylonychia (Krause, Bräucker & Hemmersbach, 2010) and Tetrahymena (Mogami et al, 2004) which all swim upwards. Gravity perception by Loxodes is due to an intracellular receptor system involving a structure with density >1.0.…”

Section: Graviperception and Gravikinesis/gravitaxismentioning

confidence: 80%

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

Plattner

2015

Biol Rev

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In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca -release channels, as well as signalling by cyclic nucleotides and Ca . Ca -binding proteins (calmodulin, centrin) and Ca -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca -channels, exocyst complexes and Ca -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.

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Section: Graviperception and Gravikinesis/gravitaxismentioning

confidence: 80%

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

Plattner

2015

Biol Rev

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“…[36] The present study was not designed to investigate the specific mechanism(s) of how cells might orient to the vertical gravity vector, though the question of how “gravitaxis” is achieved by microorganisms is intriguing. Physical models for how protists could passively orient vertically due solely to internal weight distribution or asymmetrical cell shape have been proposed (Kessler 1985; Roberts 2006, 2010). These mechanisms could allow negatively buoyant, motile cells to either swim upward or sink slowly depending on the beat patterns of the flagella or cilia, with the reverse occurring for positively buoyant cells.…”

Section: Discussionmentioning

confidence: 99%

Going ballistic in the plankton: Anisotropic swimming behavior of marine protists

Schuech

Menden‐Deuer

2014

Limn Fluids and Environments

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Diel vertical migrations (DVMs) of many plankton species, including single-celled protists, are well documented in the field and form a core component of many large-scale numerical models of plankton transport and ecology. However, the sparse quantitative data available describing motility behaviors of individual protists have frequently indicated that motility exhibits only short-term correlation on the order of a few seconds or hundreds of micrometers, resembling diffusive transport at larger scales-a result incompatible with DVM, which requires ballistic (straight-line) motion. We interrogated an extensive set of three-dimensional protistan movement trajectories in an effort to identify spatial and temporal correlation scales. Whereas the horizontal components of movement were diffusive, the vertical component remained highly correlated (i.e., nonrandom) for nearly all species for the duration of observation (up to 120 s and 6.1 mm) and in the absence of any environmental cues besides gravity. These persistent motility patterns may have been obscured in some previous studies due to the use of restrictive containers, dimensionally lumped, isotropic analyses, and/or an observation bias, inherent to observing free-swimming organisms with stationary cameras, which we accounted for in this study. Extrapolated over a 12-h period, conservative estimates of vertical travel ranges for the protists observed here would be 3-10 m, while diffusive horizontal motion would result in about 10 cm of travel at most. Hence, these extended observations of phylogenetically diverse swimming protists, coupled with a quantitative analysis that accounts for anisotropy in the data, illustrate the small-scale mechanistic underpinnings of DVM.

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“…Δχ is large enough to orient the vast majority of Paramecia essentially to swim vertically in magnetic fields as low as 3 T [40]. It is noteworthy that this model leaves out a hydrodynamic force dipole image torque that appears to align bacteria parallel to surfaces to trap them [6] and the gravitactic torque [29]. If the dipole torque played a role, then Paramecia that turned to parallel would stay trapped, which is contrary to the observations.…”

mentioning

confidence: 58%

“…Both behaviors disappear when Paramecia are neutrally buoyant [30,35]. The gravitactic response appears to be a passive response to a mechanical torque arising from an asymmetry of the Paramecium body [29]. The gravikinetic response, on the other hand, appears to be active.…”

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confidence: 97%

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Trapping of Swimming Microorganisms at Lower Surfaces by Increasing Buoyancy

2014

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Models suggest that mechanical interactions alone can trap swimming microorganisms at surfaces. Testing them requires a method for varying the mechanical interactions. We tuned contact forces between Paramecia and surfaces in situ by varying their buoyancy with nonuniform magnetic fields. Remarkably, increasing their buoyancy can lead to ∼100% trapping at lower surfaces. A model of Paramecia in surface contact passively responding to external torques quantitatively accounts for the data implying that interactions with a planar surface do not engage their mechanosensing network and illuminating how their trapping differs from other smaller microorganisms.

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The mechanics of gravitaxis inParamecium

Cited by 31 publications

References 21 publications

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

Going ballistic in the plankton: Anisotropic swimming behavior of marine protists

Trapping of Swimming Microorganisms at Lower Surfaces by Increasing Buoyancy

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