Figure 4: Sialic acid processing and uptake by E. coli in vitro.

(a) Growth of E. coli EHV2 in M9 minimal medium containing single monosaccharide at 10 mM. Sia, N-acetylneuraminic acid; Glc, glucose; GlcNAc, N-acetylglucosamine; GalNAc, N-acetylgalactosamine; Gal, galactose; Fuc, fucose. (b) Growth of E. coli in minimal medium containing 5 mM of 3SL and 6SL with and without supplementation of caecal fluid (CF, 1.5%, v/v) derived from WT mice. (c) CF of conventional and DSS-challenged WT and ST mice were collected. Sialidase activity was determined by measuring fluorescent 4-MU-NeuNAc at 440 nm. (d) Sialidase activity was also measured in the CF of WT and WT mice treated with either streptomycin (Stp 1 g l⁻¹), vancomycin (Van 0.5 g l⁻¹) or antibiotic cocktail (AVMN: ampicillin, Van, metronidazole and neomycin). In (c–d), the data are represented as mean±s.e.m. from two independent experiments, N=5–8, *P<0.05 (two-tailed Student’s t-test). (e) The abundance of the B. vulgatus BVU_4143 sialidase gene was determined by real-time PCR from caecum samples of WT and ST mice, and (f) caecum samples of antibiotic-treated WT mice. The data are represented as gene copy number per μg of faecal DNA. In (e–f) each data point indicates a single mouse from two independent experiments, N=5–7, *P<0.05 (two-tailed Student’s t-test).