The microbial experience of environmental phosphate fluctuations. An essay on the possibility of putting intentions into cell biochemistry.

We present a model of microbial information processing that contains characteristic features of the phenomenon of physiological adaptation. The backbone of the model is the "adaptive event" in which energy-converting subsystems of the cell interact with the changing environment. In this process, the subsystems pass, via an adaptive operation mode, from one adapted state to the next. An adaptive operation mode takes place when an adapted state is disturbed by an environmental alteration. These two manifestations of an adaptive event were differently treated in the simulation, based on an application of linear irreversible thermodynamics to the energy transduction of adaptive subsystems. In adapted states, the conductivity coefficients of the flow-force relationships employed remained constant, whereas during an adaptive operation mode, these coefficients were altered in a directional manner during the simulation. An example dealing with the complex relationship between phosphate uptake and cyanobacterial growth is given. In this example, the simulation of adapted states of two subsystems of the incorporating machinery, namely the phosphate carrier in the cell membrane and the F-ATPase in the thylakoid membrane, was in accordance with the measured uptake kinetics, and when fixed, predetermined conductivity coefficients were used. In the adaptive operation mode, however, the simulated behavior was in agreement with experimental observations when the program was able to "interpret" its own performance in the light of environmental phosphate fluctuations, experienced by the cell in the past, and to reconstruct the two subsystems according to this interpretation. Via transitions between adapted states and adaptive modes, information is transferred from one adaptive event to the next: the latter "inherits" the results of former interpretations. By appropriating them selectively, it is entering into a future in which its own interpretation is passed on to the following adaptive event. The model is discussed with respect to the concept of autopoiesis.