Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.4.2 Solvent-resistant microorganisms 867
• Changes in enzyme activities, e.g., inhibition of oxidases and depletion of ATP. Of
special relevance are various interactions with enzymes (proteins) in the membrane,
e.g., lipid-protein interactions.
• Loss of particular cellular functions, e.g., respiratory system of mitochondria or
active transport systems (see above).
• Loss of complex cell functions, e.g., reduced growth rates and activities of
microorganisms.
The extent of solvent toxicity to microorganisms is determined by various factors:
(a) Hydrophobic or lipophilic properties of solvents. The toxicity of solvents to microorganisms
can be described by a partition coefficient (log Po/w) between organic compounds
(solvents) and water which is specific for the applied substance. This partition
coefficient is based on a standard octanol-water system model. 1,15,16
The toxicity and the affinity of solvents to cell structures increase with hydrophobic
properties of solvents, e.g., high toxicities with Po/w values of 1-5. 1,14 The partition coefficient
correlates with the membrane-buffer partition coefficient between membrane and
aqueous system. 1,14,16 They also depend on membrane characteristics. 17,18
(b) Accumulation, partitioning and concentrations of solvents in cell structures (membranes).
Dissolution and partitioning of solvents depend essentially on solvent properties,
e.g., polarity (specific partition coefficients), or membrane characteristics (influence on
partition coefficients). Both dissolution and partitioning can be influenced by additional
factors, e.g., cosolvents. The effects on microorganisms can depend typically on solvent
concentrations, e.g., dose response effects.
(c) Biomass, ratio of concentrations of solvents and biomass. Effect of solvents depends
on this ratio.
(d) Surrounding conditions, e.g., temperature which influences the proton leakage and
microbial activities. 19
The toxicity of solvents for microorganisms shows positive and negative consequences,
e.g.:
• Positive aspects such as antibacterial effects 20 which are found in several products.
• Negative aspects such as reduced stability of biotransformation and bioremediation
processes because of the inactivation of microorganisms.
14.4.2.3 Adaption of microorganisms to solvents - solvent-resistant
microorganisms
14.4.2.3.1 Spectrum of solvent-resistant microorganisms
Different microorganisms are able to adapt and even to grow in the presence of solvents.
Some relevant examples are given in Table 14.4.2.2.
Table 14.4.2.2. Solvent-tolerant microorganisms and their resistance to organic
solvents
Solvent-tolerant
microorganisms
bacteria from deep sea (1.168
m, Japan)
benzene, toluene, p-xylene,
biphenyl, naphthalene
Solvents References
Abe et al. (1995) 21