Example of syntax for definition of a model for NETTO. (A) Reactions are described with a unique identifier, educts, products and an operator to set reversibility. (B) Ratios are entered either as equality constraints (=), upper bounds (>), or lover bounds (<), and are defined using the reaction indentifiers. (C) Precursor requirement for biomass formation is expressed with a list of growth-rate dependent withdrawals of metabolites in μmol/gCDW. Separate statements are used for each macromolecular class such as protein, DNA, etc.