Rational | Semi-rational | Random |
---|---|---|
Gene modifications based on knowledge of genetic mechanisms and metabolic pathways governing the phenotype | Genetic modifications based on system-level comparison between strains, conditions, etc. | Genetic changes driven by random processes |
Ex. Expression of heat-shock proteins or alcohol efflux pumps for heat or alcohol stress tolerance, respectively | Ex. Genome-wide or transcriptome-wide comparison | Ex. Laboratory evolution, induced transcription factor mutagenesis |
Dependence on availability of prior knowledge | Not limited by lack of prior knowledge | Not limited by lack of prior knowledge |
Results contribute additional information on relevant or important genes | Results contribute additional information on relevant or important genes | Results by themselves do not provide information on which genes are relevant/important |
Elucidation of mechanisms is complicated and time-consuming | High-throughput, comprehensive ‘omics’ analytical technology is required | Screening step often required to recover the improved strains |