March 18, 2011

My quest to understand the World

The title of this blog may pretend to tell you all about my big accomplishments and disappointments in my quest to understand the World. This thought may fool you! So... what am I up to?

With every experience in the field, the lab or during my studies, a very tiny bit of knowledge about the world reveals itself. You would think that this revelation will make the world less complicated... Wrong! New experiences raise new questions and new interpretations. And it acquires a newfound interest in the topic itself. It's just a matter of time before someone raises a new question in relation to the former outcome of your studies.You just keep on going. Maybe that's just the thrill of science?  The wheel of life, science and knowledge spins again.

Now... back to my work at GWL, I try to understand the life cycle of cyanobacteria in my quest to understand the World. One important feature of some cyanobacteria species is that they produce different types of cells, like in the species Anabaena and Aphanizomenon. Next to vegative cells, they produce heterocysts and akinetes (see images below).

The heterocyst is the clearly distinctive
cell with two pores that light up between
vegative cells.
The akinete is the long cell between the two vegative cells.
It is filled with spores for long term survival.

Heterocysts and akinetes are unique type of cells formed by cyanobacteria (order Nostocales and Stigonematales). 

Heterocysts are almost as big as vegetative cells, and have a different colour. They are specialized biological nitrogen-fixing cells. This means that they reduce denitrogen to ammonium, a feature that helps cyanobacteria in the process of biosynthesis. Biosynthesis plays an essential role in the metabolism and structure of the cell. They have a multi-layered cell wall, with on both sides distinctively polar plugs to transport nitrogen to the vegative cells.

Heterocysts are also a main supplier of 'new' nitrogen to the aquatic environment. They lack the process of photosynthesis and therefore contain no oxygen.

If there is already a lot of nitrogen in the water, like the by-products of fertilizers, this enables heterocystous species for not taking the effort to produce heterocysts. Why use precious energy to produce heterocyst then? Instead of producing heterocysts, they will use all their energy for growth and reproduction at enormous speed.

Clear heterocyst (A) , granular akinete (B)
and vegetative cells (the rest of the string)
in Anabaena flos-aquae. Olympus IX 70, DP72 and
cellSens Standard at 300x magnification oil. 
Photograph: Marta Demarteau/GWL

Akinetes, on the other hand, are remarkably large cells with an abnormal cell shape (elips or rectangle with rounded edges) and with a distinctively different function. They have an extra thick, layered cell wall. Akinetes are key for hibernation and to overcome unfavorable external conditions. They store reserve substances and are able to improve growth of cyanobacteria.

In Autumn, when the vegetative cells of akinete-forming cyanobacteria die, the akinete is able to survive in a rest stage. When the conditions are favorable again in Spring and Summer, the akinetes become active and produce new vegetative cells. Akinetes are therefore specialist cells with ultimate survival strategies!

Overall, I am surprised by the complexity of the cells of cyanobacteria - these small organisms that we mostly can't see with the naked eye. Only when they bloom, we can see a big flab of drifting cyanobacteria on the surface. And this is just a start in the world of cell biology, blue greens and chemistry! A start in my quest to understand the World...

Cyanobacteria are adapted to various environments.
Some species are so sophisticated that they
can survive in fresh, salt and brackish waters.


Bauersachs T; Schouten S & Sinninghe Damsté JS (2010) The importance of N₂-fixing heterocystous cyanobacteria in the marine nitrogen cycle, NIOZ Royal Netherlands Institute for Sea Research, Annual Report 2009 40-41

Van Dam-Mieras MCE et. al (cursusteam 1999) Cursusboeken Biologie van Cellen I, II, III en IV, Open Universiteit Nederland, Heerlen, Boek II 277-278
Simons J; Lokhorst GM & Van Beem AP (1999) Bentische zoetwateralgen in Nederland, KNNV Uitgeverij Utrecht

STOWA & Wageningen UR (2009) Giftig groen - de biologie en risico's van cyanobacteriën, Watermozaїek, Rapportnr. 2009-43