Current topics in signal transduction in bacteria

Among the signal transfer systems in bacteria two types predominate: two-co mponent regulatory systems and quorum sensing systems. Both types of system can mediate signal transfer across the bacterial cell envelope; however, t he signalling molecule typically is not taken up into the cells in the form er type of system, whereas it usually is in the latter. The Two-component s ystems include the recently described (eukaryotic) phosphorelay systems; qu orum sensing systems can be based upon autoinducers of the N-acylated homos erine lactones, and on autoinducers of a peptidic nature. A single bacterial cell contains many signalling modules that primarily ope rate in parallel. This may give rise to neural-network behaviour. Recently, however, for both types of basic signal transfer modules, it has been demo nstrated that they also can be organised in series (i.e. in a hierarchical order). Besides their hierarchical position in the signal transduction netw ork of the cell, the spatial distribution of individual signalling modules may also be an important factor in their efficiency in signal transfer. Many challenges lie hidden in future work to understand these signal transf er processes in more detail. These are discussed here, with emphasis on the mutual interactions between different signal transfer processes. Successfu l contributions to this work will require rigorous mathematical modelling o f the performance of signal transduction components, and -networks, as well as studies on light-sensing signal transduction systems, because of the un surpassed time resolution obtainable in those latter systems, the opportuni ty to apply repeated reproducible stimuli, etc. The increased understanding of bacterial behaviour that already has resulte d - and may further result - from these studies, can be used to fine-tune t he beneficial activities of bacteria and/or more efficiently inhibit their deleterious ones.