Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.4.2 Solvent-resistant microorganisms 869
- Alterations of the cell envelope structure (cell wall). Mechanical alterations and
chemical modifications of the cell wall can reduce the microbial resistance to solvents. The
most interesting chemical modification concerns hydrophobic or hydrophilic abilities of the
cell wall. 37 Decreasing hydrophobicity of the cell wall enhances the adaption of microorganisms
to solvents. 38
- Suppression of the effects of solvents on membrane stability.
- Limitation of solvent diffusion into the cell (see above).
- Repairing mechanisms, e.g. enhanced phospholipid biosynthesis.
- Transport or export systems. The excretion of compounds out of the microbial cell
and cytoplasmatic membrane is well known but only documented for some substances, e.g.,
for drugs. 39 Passive and active transport systems are relevant, e.g., ATP driven systems. Export
systems for the several solvents must be assumed.
- Immobilization and mobilization of microorganisms and solvents. The adsorption of
solvents to microorganisms can be reduced if the contact is decreased. For instance, immobilization
of microorganisms or solvents minimizes the contact. An immobilization and reduction
of toxicity was shown if adsorption materials were added. 40
- Surrounding conditions, e.g., low temperature, which can induce higher solvent resistance
of microorganisms (see above).
14.4.2.4 Solvents and microorganisms in the environment and industry -
examples
Microorganisms are frequently observed in organic-aqueous systems containing solvents
are essential in natural and in industrial processes. The occurrence and role of microorganisms
and organic compounds in these two-phase organic-aqueous systems are similar to the
effects described above (see Section 14.4.2.2). Although toxic effects on microorganisms in
these natural and industrial processes are well known, reliable data concerning solvent-resistant
microorganisms are not available.
14.4.2.4.1 Examples
14.4.2.4.1.1 Biofilms, biofouling, biocorrosion
Important examples for organic-aqueous systems are surface-associated biofilms which are
a form of existence of microorganisms. Microorganisms, mostly bacteria, are embedded
into a glycocalyx matrix of these biofilms. 41,42 This biofilm matrix mediates the adhesion of
microorganisms to surfaces, concentrates substances and protects microorganisms from
antimicrobial agents. 41,42 Several organic-aqueous systems can be observed, especially surface
of surrounding materials (pipes, etc.) in relation to water or ingredients (e.g., oil in
pipes) related to water between ingredients and surrounding materials (pipes, etc.).
Some aspects of solvents in these organic-aqueous biofilm systems are studied. Solvents
can occur in water systems emitted from surrounding organic materials. 43 It was
shown that solvents are important concerning microbial biocorrosion and biofouling processes,
e.g., by swelling and hydrolysis of materials. 44
Despite these well-known aspects, reliable data and studies concerning solvent-resistant
microorganisms in biofilm, biofouling, or biocorrossion processes are not shown. Nevertheless
similar mechanisms in biofilms must be assumed as described above (see Section
14.4.2.3) because similar conditions occur (organic-aqueous systems).