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Both mutants were grown on 2,7-anhydro-Neu5Ac (orange), Neu5Ac (blue), glucose (red), or M9 medium alone (black) in 200-µl microtiter plates. All strains were grown on 2,7-anhydro-Neu5Ac (orange), Neu5Ac (blue), glucose (red), or M9 medium alone (black) in 200-µl microtiter plates. Structure of the sialometabolic nan regulon of E. coli K12 strains and the role of YjhC in sialometabolism by E. coli BW25113. A, structure of the complete sialometabolic regulon of E. coli K12 strains. Growth of sialometabolism E. coli BW25113 transporter mutants. B-D, growth of E. coli on different carbon sources. Deletion of yjhC resulted in loss of growth on 2,7-anhydro-Neu5Ac but not on Neu5Ac (Fig. 5C), which could be complemented in trans with yjhC (Fig. 5D), suggesting that the gene encodes an equivalent protein to RgNanOx. To test the hypothesis that other bacteria can act as "scavengers" of 2,7-anhydro-Neu5Ac, we heterologously expressed and purified the NanOx protein from Hemophilus hemoglobinophilus and showed that the recombinant protein was active against 2,7-anhydro-Neu5Ac (Fig. 6). The analysis also revealed two additional couplings of NanOx-like genes to likely 2,7-anhydro-Neu5Ac transporters, namely to transporters of the SSS family, for example in Streptococcus pneumoniae TIGR4 and a transporter of the GPH family in Lactobacillus salivarius (Fig. 8), which, together with the phylogenetically broad occurrence of the NanOx-like genes, suggests that 2,7-anhydro-Neu5Ac use is not a new trait in bacteria but the result of a symbiotic evolution of bacteria in the mammalian gastrointestinal tract.