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Abstract

Rhodococci are ubiquitous in nature and their ability to metabolise a wide range of chemicals, many of which are toxic, has given rise to an increasing number of studies into their diverse use as biocatalysts. Indeed rhodococci have been shown to be especially good at degrading aromatic and aliphatic nitriles and amides and thus they are very useful for waste clean up where these toxic chemicals are present. The use of biocatalysts in the chemical industry has in the main been for the manufacture of high-value fine chemicals, such as pharmaceutical intermediates, though investigations into the use of nitrile hydratase, amidase and nitrilase to convert acrylonitrile into the higher value products acrylamide and acrylic acid have been carried out for a number of years. Acrylamide and acrylic acid are manufactured by chemical processes in vast tonnages annually and they are used to produce polymers for applications such as superabsorbents, dispersants and flocculants. Rhodococci are chosen for use as biocatalysts on an industrial scale for the production of acrylamide and acrylic acid due to their ease of growth to high biomass yields, high specific enzyme activities obtainable, their EFB class 1 status and robustness of the whole cells within chemical reaction systems. Several isolates belonging to the genus Rhodococcus have been shown in our studies to be among the best candidates for acrylic acid preparation from acrylonitrile due to their stability and tolerance to high concentrations of this reactive and disruptive substrate. A critical part of the selection procedure for the best candidates during the screening programme was high purity product with very low residual substrate concentrations, even in the presence of high product concentrations. Additionally the nitrile and amide substrate scavenging ability which enables rhodococci to survive very successfully in the environment leads to the formation of biocatalysts which are suitable for the removal of low concentrations of acrylonitrile and acrylamide in waste streams and for the removal of impurities in manufacturing processes.

Nitrile‐converting enzymes: An eco‐friendly tool for industrial biocatalysis

“…Entrapment in hydrogels such as calcium alginate , barium alginate , pectinate, k‐carrageenan, and polyacrylamide was used for immobilization of nitrile‐converting enzymes . Some of the immobilized preparations showed a marked thermal or chemical stability.…”

Membrane transport systems and the biodegradation potential and pathogenicity of genus Rhodococcus

“…The most successful industrial application of Rhodococcus spp. is probably the production of acrylamide by the Nitto Chemical Industry, Co. in Japan (Hughes et al, 1998; Raj et al, 2008; Tao et al, 2009). Rhodococcus strains are able to degrade and/or convert highly recalcitrant compounds including aliphatic-, monoaromatic-, and polyaromatic hydrocarbons, as well as heterocyclic aromatic compounds making them suitable in biocatalytic and bioremediation processes (de Carvalho et al, 2007; Pieper and Seeger, 2008; Martínková et al, 2009; Tyagi et al, 2011).…”

Comparative and Functional Genomics of Rhodococcus opacus PD630 for Biofuels Development

“…Rhodococcus species present an attractive target for industrial processes due to high substrate tolerances and high density culturing on a rapid time scale as compared to many photosynthetic organisms [5], [6]. The oleaginous metabolism of Rhodococcus goes beyond abundant lipid biosynthesis to include diverse hydrocarbon catabolism.…”