Fig. 4.

Growth yields of orthologous gene pairs. Orthologous gene pairs that are non-essential in E. coli but inferred as essential in Shigella (blue) tend to exhibit low growth yields in E. coli. ORFs that we infer to be uniquely essential in Shigella consistently have E. coli orthologues with low growth phenotypes in LB media after 22 h (apparent as a strong leftward shift in the cumulative curve). For genes inferred as uniquely essential in Shigella, 32 % of the orthologous E. coli deletion genotypes exhibit low growth yields (less than 0.5 OD600 after 22 h of growth in LB). For genes we classified as non-essential in Shigella and E. coli only 3.6 % exhibit low growth yields. Thus, some genes we infer as essential in Shigella may not be strictly essential, but instead be required for robust growth. Despite this enrichment for low-growth phenotypes, there are many genes which we infer as essential in Shigella, but which have E. coli orthologues whose deletion genotypes exhibit robust growth (OD600 greater than 0.75 after 22 h growth in LB)