Biotransformation using solvent-tolerant microorganisms

Aono et al. reported the oxidative bioconversion of cholesterol as a model biocatalytie reaetion using a solvent-tolerant Pseudomonas species. Cholesterol and its 

Speelmans et al. reported on the bioconversion of limonene to perillic acid by a solvent-tolerant Pseudomonas putida. The microbial toxicity of limonene is known to be very high. It is a major component of citrus essential oil and is a cheap and readily available base material. By using a solvent-tolerant strain perillic acid was obtained at a high concentration. This finding brings commercial production nearer. 

The applications of solvent-tolerant strains in microbial production processes are at present limited, but two strategic options are currently available to use such bacteria. Relevant genes can be introduced into solvent-tolerant organisms in order to produce the required product. This approach has been followed successfully by J. Wery in our laboratory who employed an 1-octanol-aqueous system. Methylcatechol was produced from toluene by solvent tolerant P. putida S12. Alternatively, the efflux pump can be expressed in a suitable solvent-sensitive host which would then be more tolerant for a particular solvent. 

Other benefits may arrive from solvent-resistant bacteria. Ogino et al. isolated Pseudomonas aeruginosa LST-03 whieh ean grow in organic solvents with logPo/w 2.4 and secrets organic solvent-stable lipolytic enzymes. They were able to purify an organic solvent-stable protease which was more stable than the commercially available proteases. Hence, solvent-tolerant strains have become a source for new enzymes. 

In the near future, the use of solvent-tolerant strains will make the application of organic solvents in biotransformations by whole cells a more realistic option. 

Many important fine chemicals, including catechols, phenols, aldehydes and ketones, low molecular epoxides and diepoxides, medixun-chain alcohols, and terpenoids fall within the range of 1 log Pq/w 4. The discovery of solvent-tolerant bacteria leads to the new possibility of biocatalytic reaction systems containing organic solvents. By using solvent-tolerant bacteria, a variety of fine chemicals can be formed in microbial production processes. 

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