pectins and formic-acid

Fusarium culmorum and Fusarium oxysporum are the most common fungal pathogens of flax (Linum usitatissimum L.), thus leading to the greatest losses in crop yield. A subtractive cDNA library was constructed from flax seedlings exposed for two days to F. oxysporum. This revealed a set of genes that are potentially involved in the flax defense responses. Two of those genes directly participate in cell wall sugar polymer metabolism: UDP-D-glucuronate 4-epimerase (GAE; EC 5.1.3.6) and formate dehydrogenase (FDH; EC 1.2.1.2). GAE delivers the main substrate for pectin biosynthesis, and decreases were detected in its mRNA level after Fusarium infection. FDH participates in the metabolism of formic acid, and the expression level of its gene increased after Fusarium infection. However, metabolite profiling analysis disclosed that the pectin content in the infected plants remained unchanged, but that there were reductions in both the levels of the soluble sugars that serve as pectin precursors, and in the level of formic acid. Since formic acid is the product of pectin demethylesterification, the level of mRNAs coding for pectin methylesterase (EC 3.1.1.11) in the infected flax was measured, revealing a decrease in its expression upon plant infection. Transgenic flax plants overexpressing fungal polygalacturonase (EC 3.2.1.15) and rhamnogalacturonase (EC 3.2.1.-) showed a decrease in the pectin content and an elevated level of formic acid, but the level of expression of the FDH gene remained unchanged. It is suspected that the expression of the formate dehydrogenase gene is directly controlled by the pathogen in the early stage of infection, and additionally by pectin degradation in the later stages.

Topics: Amino Acids; Carbohydrate Epimerases; Carbohydrate Metabolism; Carboxylic Ester Hydrolases; DNA, Complementary; Flax; Formate Dehydrogenases; Formates; Fusarium; Gene Expression Regulation, Plant; Glycoside Hydrolases; Host-Pathogen Interactions; Pantothenic Acid; Pectins; Plant Diseases; Plants, Genetically Modified; Polygalacturonase; RNA, Messenger; Seedlings

To compare fermentation pattern in cultures of Bacteroides caccae supplied with pectin and glucose, and identify enzymes involved in metabolism of pectin.. A strain KWN isolated from the rabbit caecum was used. Fermentation pattern, changes of viscosity and enzyme reactions products were determined. Cultures grown on pectin produced significantly more acetate and less formate, lactate, fumarate and succinate than cultures grown on glucose. Production of cell dry matter and protein per gram of substrate used was the same in pectin- and glucose-grown cultures. The principal enzymes that participated in the metabolism of pectin were extracellular exopectate hydrolase (EC 3.2.1.67), extracellular endopectate lyase (EC 4.2.2.2) and cell-associated 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase (EC 4.1.2.14). The latter enzyme is unique to the Entner-Doudoroff pathway. Activities of pectinolytic enzymes in cultures grown on glucose were low. Activity of KDPG aldolase was similar in pectin- and glucose-grown cells.. Metabolites and activities of pectin-degrading enzymes differed in cultures of B. caccae KWN grown on pectin and glucose. Yields of dry matter and protein were the same on both substrates.. Information on metabolism of pectin in animal strains of Bacteroides is incomplete. This study extends the knowledge on metabolism in bacteria from the rabbit caecum.

Topics: Acetates; Aldehyde-Lyases; Animals; Bacterial Proteins; Bacteroides; Biomass; Cecum; Fermentation; Formates; Fumarates; Glucose; Lactic Acid; Pectins; Polygalacturonase; Polysaccharide-Lyases; Rabbits; Succinic Acid

Topics: Anti-Bacterial Agents; Antibiotics, Antitubercular; Dermatologic Agents; Formates; Pectins