For phenolic compounds, the production of reactive oxygen species (ROS) is known for aerobic bacteria containing of enzymes using molecular oxygen as substrates (Tamburro et al., 2004). Obviously, these effects are greater in

the case of methanotrophic bacteria, with their very high activity of oxygen-depending enzymes such as the MMO. Thus, the activity of the MMO in the presence of aromatic compounds leads to an increased generation of oxidative stress that causes the occurrence of toxic ROS, resulting in various Lumacaftor mw cellular deleterious effects such as damage to proteins, lipids and nucleic acids. A concentration-dependent production of ROS in the presence of 4-chlorophenol was already verified in the bacterium Ochrobactrum anthropi (Tamburro et al., 2004). The PS-341 clinical trial very high sensitivity

of M. capsulatus towards organic solvents especially phenols might also have consequences in terms of the effect of methane on global warming (Crutzen, 1991; Oremland & Culbertson, 1992). Aliphatic and aromatic compounds represent one of the major pollutants of soils and waters worldwide. Taking into consideration that up to more than 80% of methane that is formed in the lower anaerobic parts of soils are degraded in the upper 30 cm by aerobic methanotrophic bacteria (Oremland & Culbertson, 1992), an anthropogenic pollution of soils by aromatic xenobiotic compounds might also lead to an increased overall release of this effective greenhouse gas into the atmosphere as it was already reported for nitrogen fertilizers (Steudler et al., 1989; King & Schnell, 1998). Figure 3 shows the effect of 1-decanol on the growth rate and the trans/cis ratio of unsaturated fatty acids. A direct relation between Terminal deoxynucleotidyl transferase the added concentration of the toxin, its toxicity and the cis–trans isomerization could be observed (Fig. 3). This effect of toxic solvent concentrations is another physiological evidence for the presence of a cis–trans isomerase

of unsaturated fatty acids in M. capsulatus. However, the solvents’ effects on the cis–trans isomerization were different regarding the class of compounds tested as well as the toxicity/hydrophobicity of the alkanols and phenols added to the cells. In the presence of toxic concentrations of chlorinated phenols, aldehydes and short-chain alkanols, the effect was less intense than in the presence of long-chain alkanols such as 1-hexanol, 1-octanol and 1-decanol. In order to allow a better comparison of the results, the maximum changes in the trans/cis ratios obtained for all tested compounds were calculated (Table 3). In addition, Fig. 4 shows the highest differences in the trans/cis ratios (Δtrans/cis) of unsaturated fatty acids caused by the investigated organic compounds according to their log P values. This blot indicates well that the different compounds also caused a qualitatively different reaction at the level of cis–trans isomerization of the membrane lipids.