High-value metabolites

Solid-substrate fermentation processes (SSF) are four-phase systems, where air flows through a solid bed containing a water-insoluble support and a nutrient-rich aqueous solution. This technology is used to produce many high-value metabolites, such as antibiotics, biopesticides, aromas and enzymes. 

Nutraceutics and High Value Metabolites Produced by Lactic Acid Bacteria... 

In past years, LAB applications have moved beyond the traditional food fermentation processes to use in delivery of molecules (Martin et al. 2014) and as microbial cell factories for producing value-added products (Boguta et al. 2014). In this chapter the capability of LAB to naturally produce nutraceutics and high value metabolites is discussed the use of recombinant LAB for production of commodity chemicals is presented briefly. 

Here, a portfolio of high-value metabolites produced by wild-type LAB displaying applications in the food, pharmaceutical, and chemical industries was presented. New approaches in the production of commodity chemicals, to replace natural resources, by recombinant LAB strains were briefly addressed. The versatility of this bacterial group demonstrates their potential to be used as cell factories beyond their classical use as food starter cultures, preservatives, or as probiotics. As shown, LAB are systematically screened for novel specific traits or applications thanks to the availability of novel molecular techniques and consumers demands for healthier, tailor-made foods. It is clear that application of LAB as the workhorses of the food industry has expanded to their use as microbial factories to increase yields and product repertoire which were earlier limited by the natural capacity of the existing bacterial biosynthetic pathways. Emerging fields include the design and creation of synthetic microbes to create novel metabolic pathways for new products. Will LAB be included in this next challenging approach ... 

In many cases, food crops are exploited to provide abundant sources of carbohydrates and oils that are then diverted to industrial uses, for example corn, potatoes and wheat for starch, and oilseed rape and sunflower for oil. In other cases, nonedible crops are commercialised primarily for specific industrial or medicinal use, where examples include linseed, castor bean and rubber palm. Where plants are commercialised for industrial uses, unless products command a very high value, candidate plants must be capable of producing large quantities of the metabolites of interest. In the case of oils for specific uses, this means plants must be enriched in specific fatty acids. This arises from the fact that plant-derived chemicals in many cases compete with petrochemical-derived alternatives and this requires that costs of extraction and refining are kept as low as possible in order to remain commercially competitive. 

There exist countless publications about the general as well as specific culture conditions of bacteria and, in particular, actinomycetes used to produce secondary metabolites. One of the best introductions to the field of fermentation is provided by the Manual of Industrial Microbiology and Biotechnology published in 1999 with Demain and Davies as the editors in chief.68 Countless scientific publications, e.g. The Journal of Antibiotics, give excellent additional information on the subject, but it should be noted that industrial processes for high-value products are usually not published in detail and are kept as company intellectual property or trade secrets. 

Batch Less generations, thus less genetic instability Easier to keep sterile Flexibility in number of products produced Allows for production of secondary metabolites Used for high-value products Can have large variability from batch to batch. Lower productivity than continuous... 

Fed-batch Allows for intermittent removal of inhibitory product Allows for addition of inducers Allows for low feed rate for production of secondary metabolites Used for high-value products Lower productivity than continuous Maintenance of sterility more difficult than batch... 

An interesting application of this assay revealed that although the insect growth regulator S-methoprene had relatively high values for 96-h LC50 and 96-h EC50, the values for metabolites produced by photolysis and hydrolysis were lower (La Clair et al. 1998) in particular those in which hydrolysis of the ester had occurred displayed serious eye deformations. 

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