Information Storage by Cyanobacteria and Algae

Cyanobacteria and eukaryotic algae have to grow in Takes under conditions, under which the supply of phosphate is subject to constant alterations. In this situation the organisms can only grow continuously, when they are able to adapt efficiently to fluctuations in the external phosphate concentrations by a constant flux of structural modifications. Thereby the energy utilization for phosphate uptake and for photosynthesis are conformed to each other in a great many ways, so that the whole metabolism is affected. This adaptation process obeys a logic which is based an complex information processing, insufficiently understood at present. In order for such an information processing to occur, the external phosphate concentration is dissected by the uptake activity of the whole population into single pulses, so that during intermittent phosphate supply short-term rises in the external concentration are interrupted by Tonger periods in which this nutrient is not incorporated. Under this condition the microorganisms adapt to the form of these pulses, store information about the adaptive event and utilize this information for subsequent adaptations in following pulses. This mechanism ensures that during each pulse sufficient phosphate is accumulated in order to cover the continuous demand of the growing cell. Essential for the functioning of this mechanism is the capacity to preserve information about previous adaptations during periods in which no uptake occurs. This information storage can be considered as a simple form of "memory" for the response to challenges by elevated phosphate concentrations. lt is interesting that information about environmental alterations, "experienced" by the microorganisms, can be transferred to daughter generations. As a result, environmental experiences of mother and grand mother cells are imprinted in a distinct way upon the behaviour of daughter and grand daughter cells. The here described project deals with a characterization of this memory in organisms originating from different biotopes. Apart from an investigation of the forms and patterns of pulses which are required to engender such an information storage, also the mutual adaptation of energy converting subsystems, performed during information storage, shall be investigated. Furthermore, an attempt shall be made to use this memory phenomenon for quantifying diffuse phosphate discharge into lakes.

The project investigated the interrelation between experience of environmental alterations and self constitution in simple organisms. The study is based on analogies between experience and the phenomenon of physiological adaptation. Setting out from the fact that every new experience proceeds in the context of a prehistory of experiences, we asked to what extent an adaptive response is influenced by preceding adaptations and whether a cellular "memory" can be detected in the connectivity of adaptive events. Using the phosphate uptake system of cyanobacteria as model system for investigating its adaptive response to environmental phosphate fluctuations, we discovered that cyanobacteria are capable of discriminating between different patterns of phosphate fluctuations, even if during these fluctuations the same amount of phosphate had been incorporated. The cells then use information about these different patterns for regulating the subsequent adaptive behaviour of the phosphate uptake system in a distinct way. Under certain conditions information about fluctuation patterns is transferred to daughter cells. A computer simulation of the phosphate uptake process, using a network thermodynamic model of the conversion of external phosphate into an internal polyphosphate store, allowed analyzing this phenomenon. In this model phosphate incorporation is performed by a system, in which two energy converting subsystems permanently communicate about alteration of the external phosphate concentration. One subsystem is the phosphate carrier that transports phosphate through the cell membrane into the cell; the other is the ATP-synthase that converts the internal phosphate into an energy rich intermediate, needed for the formation of polyphosphates. During this communication the two energy converting subsystems conform to each other in a sequence of interconnected adaptive events, in which they alternatively attain adapted states and adaptive operation modes. In adapted states the subsystems utilize available energy with optimal efficiency. In adaptive operation modes they `interpret` alterations in phosphate supply and the adapted state of the other subsystem in the light of phosphate fluctuations, experienced by the cell in the past; thereby they reconstruct themselves in order to establish a new adapted state, in which they operate efficiently again under the altered conditions. By this communication process a cell constantly `observes` ambient phosphate fluctuations and regenerates itself. Any adaptive response to an environmental alteration is a function of the dynamics of this communication, which, in turn, is differently modulated by different environmental stimuli. By this mechanism antecedent environmental phosphate fluctuations potentially influence subsequent adaptive responses in a great many ways. The phosphate uptake processes, simulated by the computer, were in accordance with the experimentally observed behaviour, when the program operated in a self-referential manner, adjusting during the simulation alternately the parameters of the two subsystems to each other and to the calculated external and internal phosphate concentrations.