H. somnus produces an exopolysaccharide that contains mannose and galactose, whose production is upregulated when the bacteria are grown anaerobically and in high salt (T.J. Inzana, A. Cox, and G. Glindemann, Abstr. 102nd General Meeting of the American Society for Microbiology, abstr. Z-26, 2002) (40). We found in H. somnus 129Pt all but one of the genes involved in the pathways leading to GDP-D-mannose and GDP-D-galactose (Table S16), which are incorporated into the exopolysaccharide of Burkholderia cepacia (39). The genes necessary for GDP-D-galactose synthesis included phosphoglucomutase (HS_0730), UDP-glucose pyrophosphorylase (galU; HS_1117) and UDP-glucose epimerase (galE; HS_0789). For GDP-D-mannose synthesis, the genes that were present in H. somnus 129Pt included phosphoglucose isomerase (pgi; HS_0938), phosphomannose isomerase/mannose-6-phosphate isomerase (manA; HS_0605) and phosphomannomutase (manB; HS_1118 and HS_1670). Missing from H. somnus 129Pt was the manC gene encoding GDP-D-mannose-pyrophosphorylase, which catalyzes the last step in the formation of GDP-D-mannose, the conversion of mannose-1-phosphate to GDP-D-mannose.
