Do the tiny hairs on algal flagella help the cell swim?
Removing the fine hairs from Chlamydomonas flagella does not change how fast the cells swim, how their flagella beat, or how much fluid they push.
Source
Fibrous Flagellar Hairs of Chlamydomonas reinhardtii Do Not Enhance Swimming
Study at a glance
- Design
- Other — Lab comparison of a hairless mutant (mstg) with two hair-bearing strains using free-swimming tracking, flagellar waveform analysis, optical-tweezers flow measurements and boundary-element Stokes simulations of smooth flagella.
- N
- No single N: 51, 53 and 52 swimming tracks (cc125, cw15, mstg); 6 cells per strain for waveform analysis; 9 to 14 cells per strain for flow measurements.
- Population
- Three strains of the green alga Chlamydomonas reinhardtii: wild type cc125, cell-wall-deficient cw15, and mastigoneme-deficient mutant mstg
- Outcome
- Swimming speed, beat frequency and turning rate; flagellar waveform parameters; local flow velocities around beating flagella and agreement with smooth-flagellum simulations
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
The researchers compared a mutant alga lacking flagellar hairs (mastigonemes) with its hair-bearing parent strain and with wild-type cells, after confirming the hairs' presence or absence by electron microscopy. They filmed freely swimming cells at high speed, measured the flagellar waveform of cells held on a micropipette, and used an optically trapped bead as a flow probe to measure the flow generated near beating flagella. They then simulated the flow around each cell with a Stokes-flow model that treats the flagella as smooth cylinders and compared it with the measurements.
What they found
Mean and maximum swimming speeds did not differ significantly between cells with and without hairs, and waveform curvature, amplitude and wavelength were also statistically indistinguishable. The measured flows decayed with distance as expected for a point force and showed no differences between strains beyond normal cell-to-cell variation. The smooth-flagellum simulation matched all three strains equally well, with errors around 0.15 of the flow amplitude, whereas rigid hairs would have raised flagellar drag by an estimated 30% to 50%. The hairless mutant did turn more often, but this was traced to asymmetric or desynchronised beating rather than to hydrodynamics.
The limits
What it doesn't show
The study does not reveal what the hairs are for; the authors suggest sensing, adhesion or feeding but test none of these. The mutant also lacks a cell wall, so comparisons depend on the cell-wall-deficient cw15 strain as the proper control, and wall loss itself changed beat frequency. The proposed explanation, that the hairs are too flexible to add drag, was not measured, since hair bending stiffness was not determined. Waveform analysis used only six cells per strain, so small differences could have been missed.
Key terms
- Mastigonemes
- Nanometre-thin hair-like fibres attached along some eukaryotic flagella, long thought to increase the flagellum's effective width and thrust.
- Low Reynolds number / Stokes flow
- The regime of microswimmers where viscous forces dominate inertia, so fluid motion obeys the linear Stokes equations.
- Optical tweezers velocimetry (OTV)
- Measuring local fluid velocity from the tiny displacement of a laser-trapped bead, using the trap stiffness to convert displacement into force.
- Stokeslet
- The flow produced by a point force in a viscous fluid; its velocity falls off as one over distance.
- Boundary element method (BEM)
- A numerical method that solves the flow equations using only the surfaces of objects, here the tracked flagellar shapes.
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Quiz yourself
What was the main conclusion about mastigonemes in Chlamydomonas?
Common questions
Why compare against the cw15 strain rather than only wild type?
The hairless mutant was made from cw15, which also lacks a cell wall, so cw15 isolates the effect of the hairs from the effect of losing the wall.
If hairs help another alga, Ochromonas, why not Chlamydomonas?
Models show hairs only add drag if they are stiff enough; the thin fibrous hairs of Chlamydomonas may bend with the flow and so act like a smooth flagellum.
Why did the hairless cells turn more?
Video showed their two flagella more often slipped out of synchrony or swept unequal areas, which turns the cell; the flow data show this is not a direct drag effect of the hairs.
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