Handbook of Solvents - George Wypych - ChemTech - Ventech!

860 M Matsumoto, S Isken, JAMdeBont
Solvent
log P O/W
Pseudomonas putida
IH-2000
Pseudomonas putida
IFO3738
Pseudomonas
fluorescens IFO3507
Escherichia coli IFO3806
Achromobacter
delicatulus LAM1433
Alcaligenes faecalis
JCM1474
Agrobacterium
tumefaciens IFO3058
p-xylene 3.1 + + - - - - - - -
styrene 2.9 + - - - - - - - -
toluene 2.6 + - - - - - - - -
benzene 2.1 - - - - - - - - -
+, growth; -, no growth
Bar 9 suggested that the toxicity in two-phase systems was caused by both the presence
of a second phase (phase toxicity) and solvent molecules which dissolved in the aqueous
phase (molecular toxicity). Basically, both mechanisms are governed by the same principle
in that the solvent accumulates in the microbial membrane. In case of the direct contact between
cells and pure solvent, the rate of entry of solvents in a membrane will be very high. If
the solvent has to diffuse via the water phase, then the accumulation in membranes will be
slower. This latter mechanism on the molecular toxicity has been investigated in more detail.
17 In experiments with liposomes from E. coli, and ten representative organic solvents
labeled by 14 C under aqueous-saturating levels, it was observed that the solvents accumulate
preferentially in the cell membrane. The partition coefficients (log P M/B) of the solvents between
the model liposome membrane and buffer correlate with those (log P O/W) in a standard
1-octanol-water system:
log P M/B = 0.97 x log P O/W - 0.64 [14.4.1.1] 17
The accumulation of an organic solvent in the membrane causes changes in the membrane
structure. Organic solvents residing in the hydrophobic part of the membrane disturb
the interactions between the acyl chains of the phospholipids. This leads to a modification
of membrane fluidity which eventually results in the swelling of the bilayer. 10 In addition to
this, conformations of the membrane-embedded proteins may be altered. 10 These changes in
the integrity of the membrane also affect the membrane function.
The principal functions of the cytoplasmic membrane involve:
1) barrier function,
2) energy transduction and
3) formation of a matrix for proteins.
The disruption of lipid-lipid and lipid-protein interactions by the accumulation of organic
solvents has a strong effect on the membrane’s function as a selective barrier for ions
and hydrophilic molecules. Permeability is of particular importance for protons because the
leakage of protons directly affects the primary energy transducing properties of the membrane.
The initial rates of proton influx in the absence and presence of different amounts of
hydrocarbon were measured. 17 The permeability for protons increases with increasing
amounts of hydrocarbon. Hence, leakage of protons occurs in the presence of organic sol-
Bacillus subtilis
AHU1219
Saccharomyces uvarum
ATCC26602