Optimality and Microbial Growth Strategies

For unicellular organisms the average specific growth rate, i.e. the rate of biomass production per amount of catalyst – the biomass itself- is a direct measure of fitness. Hence, many approaches exist in microbial physiology and metabolic engineering that use growth rate optimisation as an organisational principle to predict growth strategies from mechanistic models and biological (omics) data. We proposed, much at the same time as Terry Hwa did when he introduced proteome reallocation, that protein costs must be weighted against the functional benefits of specific growth strategies. In this talk I will discuss to what extent the premise of optimality in resource allocation may hold, and provide experimental evidence for its relevance. I will discuss the mathematical properties of the constrained optimisation problem that corresponding computational models try to solve, and will illustrate their use (and limitations). I hope to convince that, although not everything is optimal in biology, evolutionary optimisation provides a powerful force through which biological systems have been shaped, and thus a useful perspective to understand biological designs.