Deep Thoughts                 

William M. Durham          

aka Mack Durham

Departmental Research Lecturer

Department of Zoology
South Parks Road

Oxford University
Oxford, OX1 3PS
United Kingdom

Email:


Departmental Website

CV

I am a Departmental Research Lecturer in the Department of Zoology at Oxford University.  I am broadly interested in the interaction between fluid dynamics and microbial ecology, especially that arising in bacteria, spermatozoa, and phytoplankton. Using a combination of laboratory experiments (ranging from µm to cm in scale), simple models, numerical simulations, and field observations, my collaborators and myself try to better understand these small but very important members of the Earth.




Recent papers:
Turbulent fluid acceleration generates clusters of gyrotactic microorganisms
Physical Review Letters

gyroacceleration

In this contribution we use a combination of experiments and modeling to demonstrate that fluid acceleration can 'hijack' phytoplankton's ability to sense the direction of gravity.  We find this new biophysical mechanism induces cells to swim into regions of enhanced fluid vorticity, triggering multifractal patchiness. While the magnitude of fluid acceleration only becomes comparable to gravity at very large turbulent dissipation rates, this mechanism may help understand phytoplankton population dynamics in biofuel production facilities, where turbulence is often more energetic than within natural aquatic environments.

Read our article here.

Selected by the editors of PRL for a Focus in Physics article.

Turbulence drives microscale patches of motile phytoplankton
Nature Communications

unmixing

Centimeter-scale patchiness in the distribution of marine phytoplankton increases the efficacy of many important ecological interactions by enhancing the rate at which cells encounter one another and their predators. We show that turbulent fluid motion, whose effect is customarily associated with mixing in the ocean, instead generates intense small-scale patchiness in the distribution of motile phytoplankton. This motility-driven ‘unmixing’ offers an explanation for why motile cells are often more patchily distributed than non-motile cells and provides a mechanistic framework to understand how turbulence, whose strength varies profoundly in marine environments, impacts ocean productivity.

Read our article here.


Press:

Highlighted Article, Human Frontier Science Program
Editor's Choice Paper, The Scientist

RedOrbit
MIT Homepage
MIT News Office


Division by fluid incision: Biofilm patch development in porous media
Physics of Fluids

division


A winner of the American Physical Society's Milton Van Dyke Award, this image illustrates that the interaction of bacterial biofilm
(green) and fluid flow (red) generates striking patterns of preferential channelization in a porous microfluidic device that mimics soil.  A full article on this phenomena is currently in preparation.

See the article here.


Thin Phytoplankton Layers: Characteristics, Mechanisms, and Consequences
Annual Review of Marine Science

thinlayers

'Thin layers' are a spectacular form of patchiness in the distribution of phytoplankton.  By confining a large number of primary producers to small depth intervals, these structures act as oases for higher trophic levels in a ocean where resources are often too scarce to permit survival.

In this review article, we survey the salient features of thin layers, the mechanisms at play and mathematical techniques used to infer them in the field, and their impacts on the marine ecosystem. We argue that the time is ripe for the development of a quantitative, predictive framework to better understand their occurrence and, consequently, their ecological repercussions.

Read our article here.


Gyrotaxis in a steady vortical flow
Physical Review Letters

Phase Diagram

We show that gyrotactic motility within a vortical flow leads to tightly clustered aggregations of microorganisms. Two dimensionless numbers, characterizing the relative swimming speed and stability against overturning by shear, govern the coupling between motility and flow. Exploration of parameter space revealed a striking array of patchiness regimes. We find that patches form under conditions typical of small-scale marine turbulence, suggesting that this mechanism may be responsible for observed microscale heterogeneity in the distribution of phytoplankton.

Read our article here.



Microbial alignment in flow changes ocean light climate

Proceedings of the National Academy of Sciences, USA



Bacterial Whirls
Whirls of E. coli 

                   
The growth of microbial cultures in the laboratory is often informally assessed with a quick flick of the wrist: dense suspensions of microorganisms produce translucent ‘swirls’ when agitated. Here, we rationalize the mechanism behind this phenomenon and show that the same process may affect the propagation of light through the upper ocean.


Read the article.

Tumbling for Stealth?

Science

C. reinhardtii avoids predation by tumbling


In this perspective article, we comment on the implications of a recent article by Polin et al. that found the phytoplankton Chlamydomonas reinhardtii can actively synchronize and desynchronize its flagella to swim in a "run and tumble" manner reminiscent of the enteric bacteria E. coli.  We suggest this movement behavior might be a strategy to reduce predator encounter rates.

Read our article here and Polin et al. here.


Disruption of Vertical Motility by Shear Triggers Formation of Thin Phytoplankton Layers
Science

Gyrotactic Trapping Copyright: Gorick, Durham, and Stocker
Thin layer development via gyrotactic trapping.

Phytoplankton in Shear
Chlamydomonas nivalis (small black dots) swimming in a variable shear flow .

In this paper we demonstrate that thin layers of phytoplankton can be generated by a coupling between motility, cell morphology, and hydrodynamic shear; a process we call 'gyrotactic trapping.'  Using a suite of physical experiments and modeling, we show that the vertical motility of phytoplankton is inhibited in regions of enhanced shear and leads to dense aggregations of phytoplankton. 

Read our article and the accompanying perspective article by Prof. Daniel Grünbaum, (Univ. of Washington).

Press:

Boston Globe
New York Times
Discovery Channel News
MIT Home Page
Science Home Page
MIT News Office
Science Daily
Science News
MIT TechTalk    see page 5
On Balance Newsletter
Physorg.com



Chris Gash - New York Times
                                                                            Chris Gash - New York Times





 

Some more pictures:

A minutes old sea urchin  
A sea urchin egg fertilized only minutes before.

Dried C.nivalis
Desiccated Chlamydomonas nivalis