Distinct Roles of β-Galactosidase Paralogues of the Rumen Bacterium Mannheimia succiniciproducens

Abstract

Mannheimia succiniciproducens, a rumen bacterium belonging to the family Pasteurellaceae, has two putative ␤-galactosidase genes, bgaA and bgaB, encoding polypeptides whose deduced amino acid sequences share 56% identity with each other and show approximately 30% identity to the Escherichia coli gene for LacZ. The M. succiniciproducens bgaA (MsbgaA) gene-deletion mutant was not able to grow on lactose as the sole carbon source, suggesting its essential role in lactose metabolism, whereas the MsbgaB gene-deletion mutant did not show any growth defect on a lactose medium. Furthermore, the expression of the MsbgaA gene was induced by the addition of lactose in the growth medium, whereas the MsbgaB gene was constitutively expressed independently of a carbon source. Biochemical characterization of the recombinant proteins revealed that MsBgaA is more efficient than MsBgaB in hydrolyzing o-nitrophenyl-␤-D-galactopyranoside and p-nitrophenyl-␤-D-galactopyranoside. MsBgaA was highly specific for the hydrolysis of lactose, with a catalytic efficiency of 46.9 s ؊1 mM ؊1 . However, MsBgaB was more efficient for the hydrolysis of lactulose than lactose, and the catalytic efficiency was 10.0 s ؊1 mM ؊1 . Taken together, our results suggest that the ␤-galactosidase paralogues of M. succiniciproducens BgaA and BgaB play a critical role in lactose metabolism and in an unknown but likely specific function for rumen bacteria, respectively. R uminant animals digest cellulosic biomass through their digestive tract and metabolize this material to produce milk, meat, wool, and hides. The rumen is the first of four stomachs in ruminant animals (5). Plant biomass is fermented by ruminal bacteria in the rumen under a relatively stable environment, characterized by a stable temperature of 39°C, a near neutral pH, and a constant oxidation-reduction potential (35, 37). More than 200 species of microorganisms in the rumen, through symbiosis or commensalism, convert plant polysaccharides to monosaccharides or disaccharides (5, 16). The resulting carbohydrates are further metabolized during fermentation by rumen bacteria into organic acids, including acetic, lactic, propionic, butyric, and succinic acids, and into methane and CO 2 (37). Among these organic acids, succinic acid is an attractive chemical building block for the manufacture of various substances, such as biodegradable polymers, surfactants, synthetic resins, and additives in food and pharmaceuticals (36).Several microorganisms, including Actinobacillus succinogenes, which enable the biotechnological production of succinic acid have been isolated from the rumen and in other habitats (8). Recently, Mannheimia succiniciproducens, which produces a large amount of succinic acid with a 67.5% yield from glucose under an anaerobic condition, was isolated from a bovine rumen (23). The Gram-negative rod, nonmotile, mesophilic, and capnophilic bacterium M. succiniciproducens belongs to the family Pasteurellaceae (23). M. succiniciproducens is unable to degrade the complex polysaccharides as...

Multi-omics revealed the effects of dietary energy levels on the rumen microbiota and metabolites in yaks under house-feeding conditions

“…Overall, the MG group contained more families of GHs, including beta-galactosidase (GH2), alpha-L-fucosidase (GH95), and beta-glucosidase (GH3, GH97, and GH51) for converting cellobiose, as well as enzymes for UDP-GlcNA (GT41), acetyl xylan esterase (CE1), and arylesterase (CE10). Yaks in the MG group may have a greater ability to break down cellulose and hemicellulose, as beta-glucosidase not only hydrolyzes lactose but also plant polysaccharides catalyzed by microbial cellulases ( Lee et al, 2012 ). Previous studies have shown the importance of β-glucosidases, specifically GH3, GH51, and GH97, in converting cellobiose to enhance cellulose hydrolases ( Chen H. L. et al, 2012 ).…”