5 December 2008
Yitzhak Pilpel
Weizmann Institute of Science
Israel
Living organisms constantly react to their surroundings in order to maintain their internal environment. But can they do better than merely responding to changes that already occurred? Can they predict the next challenge and prepare in advance? Interestingly, some ecological niches expose organisms to reoccurring sets of stimuli such that the appearance of an early stimulus may serve as a predictor for subsequent ones. We examine the capacity of natural and lab-evolved organisms to "predict" such changes. We term a regulatory strategy that captures the unidirectional temporal order of stimuli "Microbial Conditioning", in analogy to Pavlovian Classical Conditioning. We develop a mathematical model to study the key forces that can select for microbial conditioning. The model is used to predict the actual fitness gained from this regulation strategy under different environmental setups. The predictions of the model are experimentally tested and validated in a specific environment, exposure of E. coli to lactose with a preceding signal. We then observe microbial conditioning both in S. cerevisiae and in E. coli under conditions found in their natural habitats, the switch from fermentation to respiration and the passage through the digestive tract, respectively.