Species within the genus Aspergillus have a large chemical repertoire. Commodity products produced in Aspergillus cell 'factories' include citric, gluconic, itaconic and kojic acid. The use of Aspergillus niger in citric acid production dates back to 1917. Citric acid is one of the most widely used food ingredients. It also has found use in the pharmaceutical and cosmetic industries as an acidulant and for aiding in the dissolution of active ingredients. Other technical applications of citric acid are as a hardener in adhesive and for retarding the setting of concrete. Citric acid is a true 'bulk chemical' with an estimated production approximating more than 1.6 billion kg each year A. niger also has found use in the industrial production of gluconic acid, which is used as an additive in certain metal cleaning applications, as well as for the therapy for calcium and iron deficiencies. Aspergillus terreus is used for itaconic acid production, a synthetic polymer. A. oryzae is fermented for kojic acid production which is used for skin whitening and as a precursor for synthesis of flavour enhancers. Suggested reading: Microbial Production of Biopolymers

Several Aspergillus secondary metabolites also have major economic importance of which the statins and their derivatives are most profitable. These cholesterol lowering drugs are now among the mostly widely used medicines. The first statin, mevastatin from Penicillium citrinum, was discovered in Japan. The first statin approved for human use, lovastatin, is a secondary metabolite isolated from Aspergillus terreus. Lovastatin was sold under the brand named MevacorTM. The statins are merely one family of useful, biologically-active secondary metabolites isolated from Aspergillus. Other compounds with pharmacological activities include cholecystokinin and neurokinin antagonists, ion channel ligands, antifungal drugs and a host of other compounds.

Adapted from An Overview of the Genus Aspergillus by Joan W. Bennett writing in Aspergillus: Molecular Biology and Genomics

Further reading

• Aspergillus: Molecular Biology and Genomics
• An Overview of the Genus Aspergillus
• Fungal Publications
• Microbial Toxins: Current Research and Future Trends
• Microbial Biodegradation: Genomics and Molecular Biology
• Microbial Production of Biopolymers
• Probiotics Publications
• Foodborne Pathogens: Microbiology and Molecular Biology

Labels: biotechnology

The genus Xanthomonas consists of 20 plant-associated species, many of which cause important diseases of crops and ornamental plants. Individual species comprise multiple pathovars, characterized by distinctive host specificity or mode of infection. Genomics is at the center of a revolution in Xanthomonas biology. Complete genome sequences are available for nine Xanthomonas strains, representing three species and five pathovars, including vascular and non-vascular pathogens of the important models for plant biology, Arabidopsis thaliana and rice. With the diversity of complete and pending Xanthomonas genome sequences, the genus has become a superb model for understanding functional, regulatory, epidemiological, and evolutionary aspects of host- and tissue-specific plant pathogenesis.
Further reading: Damien F. Meyer and Adam J. Bogdanove Chapter 7 in Plant Pathogenic Bacteria

Furthermore, Xanthomonas strains produce the acidic exopolysaccharide xanthan gum. Because of its physical properties, xanthan gum is widely used as a viscosifer, thickener, emulsifier or stabilizer in both food and non-food industries.
Further reading: Anke Becker and Frank-Jörg Vorhölter Chapter 1 in Microbial Production of Biopolymers and Polymer Precursors

Labels: bacteriology, bacterium, biopolymers, biotechnology, xanthan, xanthomonas

Many bacteria possess the genes needed to produce cellulose. However, Gluconacetobacter xylinus (formerly Acetobacter xylinum) is used for studies of the biochemistry and genetics of cellulose biosynthesis. Structurally cellulose is a simple polysaccharide, in that it consists only of one type of sugar (glucose), and the units are linearly arranged and linked together by β-1,4 linkages only. The mechanism of biosynthesis is however rather complex, partly because in native celluloses the chains are organized as highly ordered water-insoluble fibers. Currently the key genes involved in cellulose biosynthesis and regulation are known in a number of bacteria, but many details of the biochemistry of its biosynthesis are still not clear. A survey of genome sequence databases clearly indicates that a very large number of bacteria have the genes needed to produce cellulose, and this has also been experimentally confirmed for a smaller number of organisms. The biological functions of bacterial celluloses vary among species, and range from a role as a floating device to involvement in plant root adhesion and biofilm formation.
Valla et al from Chapter 3 in Microbial Production of Biopolymers and Polymer Precursors

Further reading: Microbial Production of Biopolymers and Polymer Precursors

Labels: bacterium, biopolymers, biotechnology, cellulose

from Anke Becker and Frank-Jörg Vorhölter in Microbial Production of Biopolymers

Plant-pathogenic bacteria of the genus Xanthomonas are able to produce the acidic exopolysaccharide xanthan gum. Because of its physical properties, it is widely used as a viscosifer, thickener, emulsifier or stabilizer in both food and non-food industries. Xanthan consists of pentasaccharide repeat units composed of D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a molar ratio of 2:2:1 and variable proportions of O-acetyl and pyruvyl residues. The xanthan polymer has a branched structure with a cellulose-like backbone. Synthesis originates from glucose as substrate for synthesis of the sugar nucleotides precursors UDP-glucose, UDP-glucuronate, and GDP-mannose that are required for building the pentasaccharide repeat unit. This links the synthesis of xanthan to the central carbohydrate metabolism. The repeat units are built up at undecaprenylphosphate lipid carriers that are anchored in the cytoplasmic membrane. Specific glycosyltransferases sequentially transfer the sugar moieties of the nucleotide sugar xanthan precursors to the lipid carriers. Acetyl and pyruvyl residues are added as non-carbohydrate decorations. Mature repeat units are polymerized and exported in a way resembling the Wzy-dependent polysaccharide synthesis mechanism of Enterobacteriaceae. Products of the gum gene cluster drive synthesis, polymerization, and export of the repeat unit.

Further reading:
1. Microbial Production of Biopolymers
2. Plant Pathogenic Bacteria

Labels: bacterium, biopolymers, biotechnology, genetic engineering, xanthan, xanthomonas

Scientists at the Institute of Food Research, Norwich UK found that probiotic bacteria in a daily drink can modify the immune system's response to grass pollen. Volunteers with a history of seasonal hay fever drank a daily milk drink with or without live Lactobacillus casei over 5 months. The study was double-blinded and placebo controlled, so neither the volunteers nor the scientists knew who had been assigned the probiotic drinks.

Blood samples were taken before the grass pollen season, then again when it was at its peak (June), and 4 weeks after the end of season. There were no significant differences in levels of IgE in the blood between the two groups at the start of the study, but IgE levels were lower in the probiotic group both at the peak season and afterwards. IgE stimulates the release of histamine which produces the symptoms of hayfever.

Further reading: Lactobacillus Probiotics

Labels: bacteriology, biotechnology, lactic acid bacteria, lactobacillus, probiotics

A huge variety of biopolymers, such as polysaccharides, polyesters, and polyamides, are naturally produced by microorganisms. These range from viscous solutions to plastics and their physical properties are dependent on the composition and molecular weight of the polymer. The genetic manipulation of microorganisms opens up an enormous potential for the biotechnological production of biopolymers with tailored properties suitable for high-value medical application such as tissue engineering and drug delivery.

Microorganisms naturally produce a wide variety of carbohydrate molecules, yet large-scale manufacturing requires production levels much higher than the natural capacities of these organisms. Metabolic engineering efforts generate microbial strains capable of meeting the industrial demand for high synthesis levels. As both oligosaccharide and polysaccharide synthesis are carbon and energy-intensive processes, improved production of these products require similar metabolic engineering strategies. Metabolically engineered strains have successfully produced many carbohydrate products and many unexplored strategies made available from recent progress in systems biology can be used to engineer better microbial catalysts.

Further reading: Microbial Production of Biopolymers and Polymer Precursors

Labels: biopolymers, biotechnology, genetic engineering