Micro-Organisms Can “Predict” Enviro Changes, Proving Basic Assumptions Wrong
Scanning electron micrograph of Escherichia coli
Using two different model organisms–the E. coli bacterium and the single-celled yeast–scientist have begun unraveling a puzzling behavior of many micro-organisms: the ability to “predict” a change in environmental conditions.
It has been assumed for most of the history of micro-biological science that such micro-organisms are purely “reflexive”; they simply respond and adapt to external stimuli (such as exposure to chemicals, heat stress, or drugs). But research over he past 2 years by two different scientific teams (a Princeton team lead by Saeed Tavazoie, and, a team from the Weizmann Institute in Israel) is shaking up present understanding and over-turning basic assumptions.
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IN a 2008 paper published in Nature, Tavazoie describes how yeast cells, when exposed to heat stress, immediately began activating a large set of genes that had no apparent effect (protective) to counteract the stress. This reaction to heat stress–disconnected from an obvious defensive behavior–puzzled Tavazoie’s team, causing them to rethink what was going on at the sub-cellular level.
Yeast cells (Sacharomyces cerevisiae) in DIC microscopy
In the most recent followup paper in Nature, the Weizmann team, working with another “model” organism: the gut bacterium Escherichia coli (E. coli), observed a switch in the microbe’s metabolic behavior prior to it actually needing the new capability. the E. coli, which metabolize sugar as their main food/energy source, enter the human digestive tract via the mouth and stomach (where the sugar lactose is dominant) on their way to settling in to the lower intestines (where the sugar maltose is dominant). But upon initial exposure to lactose (earlier in its journey), the bacteria start activating genes that permit metabolism of maltose–something it will only need at some point in its future.
This “pre-inducement” of genes comes at a high-energy cost to the organism–it diverts energy resources and temporarily hinders its ability to proliferate (thus impacting, initially, its survival capacity). But what is sacrificed in the short-term is made up for in long-term advantage. The behavior appears to be “pre-adaptive”–scientists actually use the term “predictive”–and undermines the notion of microbes being purely “reflexive” life forms. There seems to be some type of “cost-benefit” analysis going on here.
The Weizmann team also investigated yeast (following up on Tavazoie’s work), and exposed the cells to the stresses that accompany alcohol brewing process. They observed that the yeast cells showed enhanced survival when such stresses were presented in their natural order, as opposed to when the team reversed this order. This is believed to be more evidence of “predictive” behavior and genetic “pre-conditioning”.
These experiments have forced scientists to re-think fundamental questions, such as: How does the organism form associations between external events and inner, preparatory states? How does it “predict” its future environment?
Of course, such organisms do not “predict” the future in the same way that you or I might (they have no neurological system to even form the rudiments of such ideas). In fact, what is going on is the result of millions of years of evolutionary “experience” gained through the combined effects of two fundamental, natural processes: mutation and natural selection. These forces interact to promote “fit” networks and communities that can interact in complex ways with their environments (and even communicate with or alter the gene functioning of other organism).
These experimental results–reported in the July 27 edition of SEED Magazine (in an article by Azeen Ghorayshi)–have broad implications for micro-biological research, and as well for the emerging new science of synthetic biology. It may be possible to make micro-organisms “learn” new genetic tricks for rapidly adapting to changing environments. Further, biologists might be able to analyze these networks to reconstruct the ecological history of that organism; quoting from the article: “…looking at what they have learned to find out where they have lived.”
photo credits: E. coli - Rocky Mountain Laboratories, NIAID, NIH Source
Yeast cells - Masur on wikipedia.org
