Synthetic approaches to understanding biological constraints

Microbes can be readily cultured and their genomes can be easily manipulated. For these reasons, laboratory systems of unicellular organisms are increasingly used to develop and test theories about biological constraints, which manifest themselves at different levels of biological organization, from optimal gene-expression levels to complex individual and social behaviors. The quantitative description of biological constraints has recently advanced in several areas, such as the formulation of global laws governing the entire economy of a cell, the direct experimental measurement of the trade-offs leading to optimal gene expression, the description of naturally occurring fitness landscapes, and the appreciation of the requirements for a stable bacterial ecosystem.

► Biological constraints are apparent at different scales, from cells to ecosystems.
► Empirical relations involving growth rates reveal intra-cellular constraints.
► Variable environments impose trade-offs and select for optimal gene regulation.
► Rugged fitness landscapes constrain the evolutionary process and its outcome.
► Stable ecosystems are constrained by their environmental and social structures.