Microbial whole cell biocatalysts

The most useful form of microbial whole-cell biocatalyst is a pure culture of a micro-organism (i.e. a single species uncontaminated with other species) that contains high levels of an enzyme (or enzymes) that will carry out the desired bioconversion. The alternative possibility of using a mixed culture of two or more different types of micro-organisms, one of which will carry out the desired bioconversion, is not recommended because mixed cultures are often unstable, due to the changing relative population dynamics of the partners. This can result in unpredictable variation in the outcome of a biotransformation. 

What is the most suitable form of the chosen biocatalyst to use There are four principal alternative forms of microbial whole-cell biocatalysts that can be considered. These are... 

The microbial sources of penicillin amidases/acylases required for side-chain removal were found and were quickly commercialised as whole-cell biocatalysts. 

Sonrces for microbial and other whole cell biocatalysts - official strain collections (selection)... 

Abstract The use of various immobilized biocatalysts in industrial research and production will be introduced. The applied catalysts span the range from isolated enzymes to microbial whole cells, and even examples of the use of plant cells and mammalian cells could be found. Approximately 65 processes have been reviewed in this article, roughly 50% of which are actual production processes in the chemical industry. The remaining 50% refer to biocatalytic transformations which were carried out at laboratory scale up to pilot scale. In this review special attention was drawn to the range of transformable substrates and the variety of different supports. 

As in vitro regeneration of SAM 1 is currently not feasible, MT reactions were often performed with live whole-cell biocatalysts to avoid the need of cofactor supply (i.e., microbial hosts expressing recombinant MTs, see next section). However, a drawback of this strategy is the relatively low intracellular concentration of endogenous SAM 1, which limits methylation capacity and, thus, leads to low product yield. Even in the biosynthesis of natural products in microorganisms, such as methylated antibiotics [69] and triterpenoids [70] or fatty acid methyl esters [71], or in the biotransformation of phenolic compounds by plant cell cultures, for example, of protocatechuic aldehyde to vanillin 28 [72], availability of SAM 1 is rate-limiting. 

In fact, successful deracemization was not achieved when using a cell-free extract of the Alcaligenes cells, which showed NADH-dependent (R)-selective ADHs active in the oxidation reaction, coupled to a NADH-dependent (S)-selective ADH for the reduction reaction. Instead, it was easily achieved when using microbial whole cells in the biooxidation reaction or when combining the same cell-free extract with a NADPH-dependent ADH. In both cases, possible short circuits between the two cofactor regeneration systems were therefore avoided, thanks to the compartmen-talization of one of the involved biocatalysts in the cells or to the use of enzymes with different cofactor specificity. 

Lipases used for FAAE production are normally of microbial origin, such as CALB and TLL lipase. They are often used in immobilized forms, which are more stable and versatile than their free forms (Shimada et al, 2002 Kojima et al, 2004 Nielsen et al, 2008). The immobilized form is also more industrially feasible, as they can be easily packed and reused in industrial reactors. Nevertheless, they are also more costly in terms of enzyme price (per kg of immobilized enzyme). However, the stable and reasonably high productivity of the enzyme (kg of biodiesel/kg of immobilized enzyme) during a relatively long lifetime is more important than the sole price comparison. Whole-cell biocatalysts which are cheaper and more robust may be appropriate for industrial FAAE production (Antczak et al, 2009). The activity of whole-cell biocatalysts depends on the fatty acid composition of the cell wall membrane. As there may be different Upases bound to the cell waU or membrane, the FAAE yield may vary (Adamczak et al, 2009). 

Production of artemisinin and paclitaxel precursors by engineered whole-cell biocatalysts from glucose. Introduction of biosynthetic genes from Artemisia annua encoding the amorphadiene synthase and amorphadiene oxidase yielded microbial strains that produce arte-misinic acid. Artemisinic acid can be chemically converted into artemisinin, introduction of the Taxus genes encoding taxadiene synthase and taxadiene 5a-hydroxy-lase resulted in E. constrains that produce key paclitaxel intermediates. The biosynthetic pathway for paclitaxel has not been fully elucidated. 

Biocatalysis covers a broad range of scientific and technical disciplines, which are geared to develop biocatalysts and biocatalytic processes for practical purposes. The natural pool of biocatalysts is extremely diverse and includes whole cells of microbial, plant or animal origin, as well as cell-free extracts and enz3rmes derived from these sources. The wide range of catalytic power offered by nature remains, however, largely imexplored. Currently, only a very small fraction of the known biocatalysts are actually being applied on a commercial scale. For example, of the approximately 4,000 known enzymes, about 400 are available commercially, but only about 40 are actually used for industrial applications. 

Over the past few years, an impressive array of epoxide hydrolases has been identified from microbial sources. Due to the fact that they can be easily employed as whole-cell preparations or crude cell-free extracts in sufficient amounts by fermentation, they are just being recognized as highly versatile biocatalysts for the preparation of enantiopure epoxides and vicinal diols. The future will certainly bring an increasing number of useful applications of these systems to the asymmetric synthesis of chiral bioactive compounds. As for all enzymes, the enantioselectivity of... 

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