Table 2.

Genes inferred as uniquely essential in Shigella

Gene(s)	Function [49]	Support for Different Physiological Roles in E. coli and Shigella
lysS	aminoacyl tRNA synthetase, tRNA modification	The lysU functional homologue is absent in Shigella [45]
proABC	proline biosynthesis	The active proline transporter putP is absent from Shigella [46]. The cryptic transporter proY may be silent, as observed in Salmonella [47], possibly necessitating proline biosynthesis
ackA pta aceEF pykF	acetate kinase phosphotransacetylase pyruvate dehydrogenase pyruvate kinase	All affect acetate accumulation [66] and utilization [23], which is required for robust growth (Shigella lacks the acetyl CoA synthetase present in E. coli K12 [67])
rfbA, rfbF, rfbG, rfc, and rfbI	sugar nucleotide biosynthesis for LPS	All except rfbA lack E. coli K12 orthologues, as this locus has been replaced by the laterally transferred wbb locus [48]
cysM	cysteine synthase B	ORFs in cysteine synthase A also depleted for inserts; 4 out of 5 sulfate ABC transporters depleted for inserts (see main text)
tufB	elongation factor EF-Tu	tufB and lepA (next entry) both are involved in translation elongation; the other ORF involved, tufA, is depleted for inserts (see main text)
lepA	elongation factor 4	See above
spr	murein DD-endopeptidase	None known
rsxB	soxR-reducing complex	None known

These genes were inferred as essential in Shigella, but have orthologous E. coli deletion genotypes that exhibit robust growth (greater than 0.75 OD600 after 22 h growth in LB). The genes in the rfb operon have no orthologues in E. coli K12 (see main text)