A generalized receptor law governs phototaxis in the phytoplankton Euglena gracilisGiometto, Altermatt, Maritan, Stocker, Rinaldo

© Micronaut, Martin Oeggerli

Phytoplankton• Primary producers in aquatic habitats• Major sink for atmospheric carbon dioxide• Inhabit the photic zone of the water column

© ESA, 2012

Active movementCilia / flagella

Buoyancy control

Response to environmental cuesChemotaxisGravitaxisPhototaxis

Phytoplankton movement

Donat P. Häder

Phototactic algae: typical features• Photopigments• Stigma• Spiral swimming

Euglena and Chlamydomonas sketches from:Jékely, G. (2009). Phil Trans R Soc B 364, 2795-2808

Video from: J. Vidyadharan and K. Foster, http://fosterlab.syr.edu

Volvox carteri

Drescher, K., Goldstein, R. E., & Tuval, I. (2010). PNAS, 107, 11171–11176

Population-level dynamics• Keller-Segel model for chemotaxis

• Advection velocity

• Chemotactic potential f[s] determines response to attractant concentration s

• Keller-Segel (1971)f[s]=log[s]

• Lapidus-Schiller (1976)Receptor law f[s]=s/(s+k), k constant

Rhodobacter sphaeroides in oxygen gradient

Bacterial band

E. Coli chemotactic rings

Tindall, M. J., Maini, P. K., Porter, S. L., & Armitage, J. P. (2008). Bulletin of Mathematical Biology 70, 1570–1607

v(x)

Tindall, M. J., Maini, P. K., Porter, S. L., & Armitage, J. P. (2008). Bulletin of Mathematical Biology 70, 1570–1607

Tindall, M. J., Maini, P. K., Porter, S. L., & Armitage, J. P. (2008). Bulletin of Mathematical Biology 70, 1570–1607

© Micronaut, Martin Oeggerli

Phototactic potential?Euglena gracilis

Eyespot absorption spectrum

B R

Strother, G., and Wolken, J. (1961) J. Protozool. 8

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Red LED Red LED

Red light

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

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Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

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Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

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Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

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norm

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d)

Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

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(re-

norm

alize

d)

Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

sity

(re-

norm

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d)

Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

sity

(re-

norm

alize

d)

Blue light

Blue LEDGiometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Alga

l den

sity

(re-

norm

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d)

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Stationary algal distribution

Keller-Segel-like phototaxis model

Population-level dynamics

Phototactic potential

v(x)

Measured

Measured

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Phototactic potential

Measured in the experimentsTypical irradiance

at sea level

Ligh

t int

ensit

yInfer f from dataStationary algal distributions

Generalized Receptor Law

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Phototactic potential

Phototactic potential

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Generalized Receptor Law

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Temporal dynamics

• Modeling vertical distribution of phytoplankton• Harvesting in photobioreactors• Transport of colloidal particles

Giometto, A., Altermatt, F., Maritan, A., Stocker, R., and Rinaldo, A., (2015) PNAS 112:7045-7050

Possible applications

CoauthorsAmos Maritan, Roman Stocker, Florian Altermatt, Andrea Rinaldo

FundingEawag Discretionary Funds

Swiss National Science Foundation

Thank you!

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Euglena picture: http://www.dr-ralf-wagner.de/

Absorption spectra:Strother, G., and Wolken, J. (1961) J. Protozool. 8

Eyespot absorption spectrum

Chloroplast absorption spectrum

B

B

R

R

Study species: Euglena gracilis