Immerse, the institute research magazine, is the annual science publication of The Fifth Estate. It stands for IIT Madras Magazine on Research in Science and Engineering, where the endeavour is not only to showcase some of the recent developments in research and innovation at IIT Madras, but also to communicate the science behind them in the simplest way possible for better understanding and appreciation. In this series we publish each of the articles from Immerse 2017. You can browse through the previous editions here.
Cooperation in nature has long been a topic of study that has fascinated scientists. The interplay between the instincts of an individual organism that prompt it to look out for itself over the well-being of even others of its own species and the possible benefits that can be gained by working together plays out amongst diverse species – in animals, plants, and microscopic organisms.
The extent of cooperation between organisms is largely size-independent. Larger animals often live solitary lives, or travel in herds or packs – examples include herbivores (like deer and antelopes) as well as predators (like lions and hyenas) – but even this cooperation has its limits. The structure of packs is often fluid, with weaker members being forced out by stronger, more dominant members. Attacks on a herd usually result in stragglers being left for dead. More closely-knit groups do emerge amongst more intelligent species – elephant herds and troops of gorillas and chimpanzees place a much larger emphasis on the survival of all their members, as does human society. As one examines smaller organisms, the various shades of grey usually resolve into black and white – either members of a species cooperate, or they don’t.
An efficient method of communication within a species is a prerequisite for cooperation. Macroscopic organisms use a combination of chemical methods (for example, via pheromones) and visual cues to communicate. As one delves into the microscopic realms of the living world, optical organs are primitive, if they exist at all – making chemicals the only viable method of interaction. Studying how these tiny organisms convey information could provide insights into how our own cells achieve the same, and could also set up useful avenues of approaches into bioengineering.
Dr R. Baskar’s group in the Department of Biotechnology at IIT Madras has pushed the envelope of scientific knowledge a little further out during their research in this field. Their work focused on an organism whose scientific name is Dictyostelium discoideum. Perhaps the most interesting and relevant feature of this organism is that it belongs to a small class of species that forms collective bodies known as slime molds.
Slime molds are an approximately 900-strong group of normally single-celled species that aren’t necessarily taxonomically related – instead, their classification into this group is prompted by their ability to aggregate, and form multicellular structures that they then use to reproduce. These unicellular organisms survive on their own in times of abundant sustenance. When food is scarce, they form a multicellular body that, as a whole, can sense and respond to external stimuli. (Most slime mold species feed on microorganisms that can be found in decomposing plant matter, and can hence be most commonly found on soil surfaces and forest floors.) The organisms that comprise slime molds are often referred to as “amoeba-like”, but they are not actually amoeba. They don’t all belong to a well-defined taxonomical kingdom – instead, they are classified for convenience under kingdom Protista (any eukaryote that is neither plant, animal, nor fungus).
Historically, however, they were thought to be fungi – a conclusion that was prompted by their method of reproduction. When these multicellular aggregates form, they become a mobile “slug” that can move, albeit very slowly, in search of food. They subsequently form stalks that produce fruiting bodies, which in turn produce spores that are dispersed via the air, finally growing to form unicellular organisms that continue the life cycle. This rather remarkable ability of slime molds to both function initially as autonomous cells, and to later aggregate and cooperate, as mentioned earlier, can only be controlled by changes in the chemical environment of the cell. Dr Baskar’s research focuses on the effects of one chemical on slime molds: caffeine.
Effect of caffeine on multiple tip formation in different Dictyostelids. A) In P. pallidum, secondary tip formation was monitored at 6 h, 9 h, 12 h and 20 h of development. B) In D. aureostipes and D. minutum, ectopic tips were observed at 2 h and 3 h, respectively after transferring the slugs in plate containing 5mM caffeine. Arrow indicates multiple tip formation at respective time intervals in different Dictyostelids. Scale bar=200μm. (source: Jaiswal, P., Soldati, T., Thewes, S., Baskar, R; BMC Developmental Biology 2012, 12:26)
Caffeine is best known as a stimulant of the central nervous system in humans – in other words, it keeps us from falling asleep. One of the main methods by which it achieves that is by inhibiting the action of adenosine (by preventing it from bonding with its receptor). Adenosine is the chemical that induces feelings of drowsiness in humans. Existing literature has established that adenosine also plays a major role in the formation and motion of the slime mold aggregate. A natural question to ask, then, is whether caffeine could play a similar inhibitory role in slime molds – and this is precisely the question that Dr Baskar’s work answers.
His group examined the effects of caffeine on two aspects of the slime mold. The first was the sizes of the aggregate formed. Experiments were carried out using a control set of organisms (a control set is a set of test cells to which no modifications have been made – a benchmark, so to speak), and sets to which caffeine or adenosine were added and forced to aggregate by starving them of a food source. It was observed that the adenosine-treated slime mold formed large aggregates, while the caffeine-treated mold formed small aggregates.The size of a slime mold colony depends on two quantities – the number of cells in the aggregate (and by extensions, the rate of cell division in the colony), and the size of individual cells. Studies revealed that both quantities are significantly lower amongst the caffeine-treated slime mold.
An obvious follow-up question is exactly how these quantities are manipulated by these chemicals. The same adenosine receptors governing drowsiness in humans are unlikely to be present in these organisms. Indeed, a different mechanism was observed – these two reagents manipulated the quantity of glucose present in the cytoplasm of the cell, which directly affects cell growth and division (as the concentration of glucose decreases, so does cell activity).
The second aspect of the slime molds that was considered was the development of the tip of the aforementioned slime mold “slug”. The tip is a region of major importance within the aggregate – it acts as a chemical pacemaker, sending periodic waves of a chemical known as cAMP propagating along the length of the slime mold and controlling its movement – an example of a chemical communication method. It is in the best interest of the slime mold to form a single tip, to prevent and signalling conflicts and to ensure uniform motion. This establishment of a single dominant tip is accomplished by high concentrations of adenosine. The addition of caffeine here leads to multiple tip formation, which in turn leads to impaired cell movement.
It is easy to see from the results of Dr Baskar’s research that caffeine and adenosine are a pair of chemicals with antagonistic effects in slime molds, similar to established results for their effects in humans – species that span the spectrum of evolution. The insight provided by these results will improve our understanding of the intricate chemical pathways that allow cells to communicate, potentially advancing pharmacological research, bioengineering methods and evolutionary studies.
Meet the Prof
Dr. Baskar R is an associate professor in the department of biotechnology. He is an expert in developmental genetics. His research interest lies in pattern formation in cellular slime molds, and mutational landscape during plant development and hybridization. You can know more about his research at https://biotech.iitm.ac.in/Faculty/RB Lab/rb.html
Meet the Author
Nithin Ramesan is a final year undergraduate student of Electrical Engineering. He likes reading, quizzing, writing, and most of all, Calvin and Hobbes.