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Research Idea
Partial synchronization of the colonial diatom Bacillaria "paradoxa"
expand article info Richard Gordon
‡ Embryogenesis Center, Gulf Specimen Aquarium & Marine Laboratory, Panacea, Florida, United States of America
Open Access

Abstract

Background

The unique gliding motion of the cells in the colonial diatom Bacillaria "paradoxa" against one another has intrigued microscopists since 1783. Both the mechanism of movement and of entrainment, which results in partial synchrony, are unsolved.

New information

Experimental and analytical methods that might help solve the synchronization enigma are proposed.

Keywords

colonial diatom, Bacillaria paradoxa, gliding motility, synchrony

Overview and background

The worldwide colonial diatom Bacillaria "paradoxa" (Ussing et al. 2005) has a unique form of motion in which the cloned cells are stacked in a one dimensional array, with each one sliding back and forth against its two neighbors, as indicated in Fig. 1 (except, of course, the two end cells, which have one neighbor each, although their exposed raphes may be active, as in noncolonial raphid diatoms: Drum and Hopkins 1966).

Figure 1.

The first ever description of a diatom was of the colonial diatom Bacillaria "paradoxa" (Müller, 1783).  Colonies are shown in various configurations between which they can smoothly transition on a time scale of seconds.

From  the  many  movies online (ALMuseum 2009a, ALMuseum 2009b, Basili 2014, BirdWhisperer46 2012, Capilla 2010, Capilla 2012, Capilla 2013, Cimellimay 2011, Do 2012, Gougi 2007, Hsiao 2015, Kersulis 2012, Kiermayer 2001, Laundon 2015, Lobban 2003, Ott 2012, Otyatatemushi 2010, Otyatatemushi 2013, PeacefulProtist 2013, Pierre microscope 2014, Rines 2001, Shilov 2014, Stetson 2015, Tonysharks 2015, uni2さんのチャンネル 2012, WLanier and Communities 2006, Yanase 2015a, Yanase 2015c, Yanase 2015b) and personal observation, it is clear that the motion is partially synchronized. The question is how? Questions that could be addressed experimentally include:

  1. The colony is embedded in the elastic, transparent material secreted by the motility apparatus of each cell (its raphes). Does this material provide a mechanical feedback, such as is apparent in the occasional small backwards motion caused by adhesion and nonlinear elastic behavior of the diatom trail in noncolonial raphid diatoms (Sabuncu et al. 2015)?.
  2. Is it possible that entrainment occurs via light piping, perhaps when the light sensitive regions at the ends of the cells (Cohn et al. 2004, Cohn et al. 2011, Cohn et al. 2004, Cohn et al. 1999) are aligned (Gordon et al. 2009)?
  3. Are there ionic/electric effects and electric polarity, as in some migrating cells (Mousavi et al. 2013), that can be sensed by nearest or further neighbors?
  4. The motion stops in the dark, with the cells forming a neat, aligned stack (Kapinga and Gordon 1992), as in the upper left of Fig. 1. In the light the motion, at least often, starts with an end cell and propagates through the colony. Is there some specific cell to neighboring cell communication? If so, how?

The name of this diatom was recently changed to Bacillaria paxillifer (O. F. Müll.) Hendy (Kociolek and Kreis Jr. 2015). However, this is out of date, since Bacillaria paradoxa (Gmelin 1788) is now recognized as a group of long debated taxonomic status (Schmid 2007) and split into three species with one of them having a variety (Jahn and Schmid 2007). In addition to these, one of the names "currently accepted taxonomically" is still Bacillaria paradoxa var. tumidula (Grunow) (Guiry 2015). As they all exhibit the same peculiar motions, for the sake of referring to them as a group I use Bacillaria "paradoxa" by which they are "better known" (Jahn and Schmid 2007).

Objectives

Here are some experimental, simulation and mathematical approaches that may be worth considering to answer these questions:

  1. Break up colonies, so we could observe colonies of sizes n = 1,2,3, etc. We already know that a single cell oscillates against the shard of its laser-killed neighbor (Drum et al. 1971), so that the oscillations are intrinsic to the cells, and not an emergent phenomenon.
  2. Do computer simulations of the cells’ motion, using various rules of interaction, to find a best match to the observed motion.
  3. Analyze movies using image processing, especially to translate the coordinate system to each cell, one at a time, to get details of its motion relative to its neighbors, and correlations versus neighbor distance.
  4. Regard the problem as an inverse synchronization problem, to derive coupling parameters from the observed motion. For the forward problem, see (Pikovsky et al. 2001).
  5. Try to entrain the motion optically, with focused light  pulses, or mechanically, with any form of micromanipulation.
  6. Visualize the cloud of raphe material around the colony using colloidal particles, and analyze its motion as the cells move, perhaps using PIV (particle image velocimetry).
  7. Measure the electric field around Bacillaria or other motile diatoms, and see if its polarity alters when they reverse direction.
  8. Bend a colony under a known force until it breaks, to measure the strength of adhesion of the cells to one another, despite their relative motion.
  9. Observe the motility of dividing cells within a colony, to see if they behave the same as cells that are not dividing, and how the daughter pair initiates relative motion between them.
  10. Analyze the motion of colonial diatoms that slide just once (Ussing et al. 2005).
  11. Observe how the motion changes with light intensity and its color.

Acknowledgements

Collaborations are welcome on any or all aspects.

Hosting institution

Gulf Specimen Aquarium & Marine Laboratory, Panacea, Florida USA

References