Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.4.1 Organic solvents in microbial production 863
Figure 14.4.1.4. Schematic picture of toluene penetration and efflux in the solvent-tolerant Pseudomonas putida
S12 [After reference 20].
membranes whereas the non-adapted cells were not. Furthermore, it was observed that in
the presence of energy coupling inhibitors, toluene accumulation was the same as in the
non-adapted cells. The amount of toluene in the cell was concluded to be kept at a low level
by an active efflux system. The presence of a toluene-efflux system is supported by genetic
research. 47,48 The pump has a striking resemblance to multidrug-efflux systems. Active
efflux pumps for solvents have also been detected in other Pseudomonas strains. 25,26,30,37
It is obvious that solvent tolerance is caused by a combination of the mechanisms described
above. Figure 14.4.1.4 shows a schematic picture of toluene penetration and efflux
in the solvent tolerant strain P. putida S12. 20 Toluene enters the cell through the outer membrane.
At present, it is unclear whether toluene passes through porins or through the
phospholipid part of the cell. The efflux pump recognizes and interacts with toluene in the
cytoplasmic membrane. Toluene is then pumped into the extracellular medium.
14.4.1.4 Biotransformation using solvent-tolerant microorganisms
Many important fine chemicals, including catechols, phenols, aldehydes and ketones, low
molecular epoxides and diepoxides, medium-chain alcohols, and terpenoids fall within the
range of 1 < log PO/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.
The organic solvents used so far in published research had to be very hydrophobic
(logPO/W > 5) in order to prevent microbial inactivation. 1 Consequently, many fine chemicals
can not beneficially produced in the presence of such solvents because they simply
would remain in the water phase and would not partition to the organic phase. The use of
solvent-tolerant microorganisms enables the use of less hydrophobic solvents (2.5 <
logPO/W < 4) and in such a system, chemicals with a1