, 1992) and Vibrio (Okuyama et al., 1991). The possible activity changes of the cis–trans isomerase have also been tested by adding organic solvents. Therefore, a systematic survey of the effects of alkanols and chlorinated phenols on the growth of M. capsulatus was carried out. The toxic compounds were added in different concentrations

to exponentially growing cell cultures. The relative growth rates in the presence of the toxic compounds were calculated using the OD values according to the method described by Heipieper et al. (1995). The sensitivity to the tested alkanols correlated selleck compound with their chain length and hydrophobicity given as the logarithm of the partition coefficients between 1-octanol and water (log Po/w or simply log P); the only exceptions were methanol, to which cells showed a very high tolerance, and ethanol, which exerted a relatively

high toxic effect click here on bacterial growth. The data are summarized in Table 3. The high toxicity of ethanol occurs most probably due to the accumulation of acetaldehyde formed by methane monooxygenase (MMO). The acetaldehyde synthesized accumulates within the cells as it cannot be further metabolized. In order to prove this, two aldehydes (formaldehyde and acetaldehyde) were also tested. Both showed an extraordinarily high toxicity. Next to their effect on membrane fluidity, additional chemical effects may also be present. For aldehydes, a chemical toxicity is known that mainly leads to the disruption of proteins by the formation

of Schiff’s bases. The tested chlorinated phenols caused a far greater toxicity than expected from previous data with other bacteria. M. capsulatus Bath showed an about 10 times higher sensitivity towards the tested phenols than all previously tested aerobic bacteria (Heipieper et al., 1994, 1995; Kabelitz et al., 2003) and even a three times higher sensitivity compared with anaerobic bacteria (Duldhardt et al., 2007) (Fig. 2). The figure also reveals that for M. capsulatus, the relation between hydrophobicity and toxicity does not show the same pattern as known for all other previously tested bacteria. Especially, the relative toxicity of phenol and lower chlorinated phenols was much Sclareol higher than expected. It is known that M. capsulatus consists of membrane insertions and thus possesses a much larger relative membrane surface than most bacteria. It may be hypothesized that this very high toxicity of phenols could be caused by the strong membrane-active and decoupling effect of these compounds. However, as the relative toxicity of phenol was much greater than that of higher chlorinated phenols, a direct effect of the phenols on the membranes cannot be the reason for this extraordinarily high toxicity.