H.J. Heipieper

Mechanisms of resistance of whole cells to toxic organic solvents

Abstract Many processes in modern biotechnology, particularly biotransformations and environmental bioremediation, are hindered by the toxic effects of organic solvents on whole cells. These compounds dissolve in the cell membrane, disturbing its integrity and effecting specific permeabilization. The hydrophobicity of a compound, expressed as its log P value, is a good indicator of toxicity. Substances with a log P value in the range 1–5 are, in general, toxic to whole cells. However, in recent years, there have been several reports of bacteria exhibiting resistance to toxic solvents. The main adaptative reactions are alterations in the composition of the membrane, particularly changes in fatty-acid composition, phospholipid headgroups, and in the protein content. One of the key processes in the adaptation of some Pseudomonas strains, enabling them to tolerate organic solvents appears to be the isomerization of cis - into trans-unsaturated fatty acids. A greater understanding of these adaptations should eventually allow biotransformation reactions to be carried out in inhospitable two-phase systems incorporating an organic phase.

Trans unsaturated fatty acids in bacteria.

The occurrence oftrans unsaturated fatty acids as by-products of fatty acid transformations carried out by the obligate anaerobic ruminal microflora has been well known for a long time. In recent years, fatty acids withtrans configurations also have been detected in the membrane lipids of various aerobic bacteria. Besides several psychrophilic organisms, bacteria-degrading pollutants, such asPseudomonas putida, are able to synthesize these compoundsde novo. In contrast to thetrans fatty acids formed by rumen bacteria, the membrane constituents of aerobic bacteria are synthesized by a direct isomerization of the complementarycis configuration of the double bond without a shift of the position. This system of isomerization is located in the cytoplasmic membrane. The conversion ofcis unsaturated fatty acids totrans changes the membrane fluidity in response to environmental stimuli, particularly where growth is inhibited due to the presence of high concentrations of toxic substances. Under these conditions, lipid synthesis also stops so that the cells are not able to modify their membrane fluidity by any other mechanism.

The cis/trans isomerisation of unsaturated fatty acids in Pseudomonas putida S12 : an indicator for environmental stress due to organic compounds

Abstract The isomerization of cis to trans unsaturated fatty acid in Pseudomonas putida , a mechanism of this bacterium to adapt its membrane to toxic environmental influences, was tested as an indicator for toxicity of 10 organic compounds (aromatics and aliphatic alcohols). A direct correlation was observed between the hydrophobicity of the compounds (logP), concentration dependent growth inhibition, and the trans/cis ratio of unsaturated fatty acids. The application of this system is discussed in terms of an indicator for toxicity and environmental stress particularly during bioremediation processes.

Cellular Toxicity of Lipophilic Compounds: Mechanisms, Implications, and Adaptations

(1994). Cellular Toxicity of Lipophilic Compounds: Mechanisms, Implications, and Adaptations. Biocatalysis: Vol. 10, No. 1-4, pp. 113-122.

Methane oxidation by Dutch grassland and peat soil microflora

Abstract The ability of Dutch grassland soil and Dutch peat soil for methane oxidation was investigated. The kinetics of methane oxidation by soil from different depths were determined in batch cultures incubated with 1; 10; 100; and 10,000 ppmv methane, respectively. All 4 applied concentrations of methane were degraded by both types of soil. Thereby, the highest oxidative activities were observed between 5 and 10 cm soil depth. Most importantly, these experiments demonstrated that this soil acts as a sink for methane even at concentrations well below 1 ppmv. Especially at higher methane concentrations (100 - 10,000 ppmv) much higher degradation rates were found in the peat soil. This also correlates with the higher methane production rates which had been observed in peat soil.

The integrated CH4 grassland project: Methane consumption by indigenous grassland microflora

Abstract Soil samples were taken from the test farm in Zegveld . In batch cultures the kinetics of methane oxidation by soil from different depths were investigated. Soil was incubated in 300 ml flasks with 1, 10, 100 and 10.000 ppmv methane, respectively. All 4 applied concentrations of methane were biologically degraded by this type of grassland soil. The highest oxidative activities, especially for lower concentrations (1–100 ppmv), were observed between 5 and 20 cm soil depth. Most importantly, these experiments demonstrated that this soil acts as a sink for methane even at concentrations well below 1 ppmv. In continuous cultures soil was incubated in columns receiving a continuous gasflow of 4 ml/min containing methane at 4 different concentrations. Thereby, all concentrations of methane were degraded continuously by this type of soil.

Assessment report on NRP subtheme “gGeenhouse Gases”: Sources and sinks of CO2CH4 and N2O, databases and socio-economic causes

Abstract The aim of the subtheme Greenhouse gases of the Dutch National Research programme on (NRP) is to quantify the sources and sinks of the major greenhouse gases to enable estimates of the future atmospheric concentration. The major part of the projects in this theme is focused on the Dutch situation, but the results can be extrapolated countries or regions. The information gained will be used for Dutch policy decisions regarding abatement of greenhouse gases. Section 1 deals with the aim and organization of Causes of climate change, and relates the scope to increased awareness of uncertainties in sources and sinks of greenhouse gases: at the start of the National Research Programme the general consensus of the scientific community was that these uncertainties were not extreme large, it is nowadays accepted that these uncertainties are larger than assumed before. The aim the Cluster CO 2 ( Section 2 ) was devoted to study the exchange between terrestrial ecosystems and the atmosphere to gain more knowledge of the “fertilization” flux. The research was mainly focused on the development of a CO 2 exchange model for grassland describing diurnal and seasonal fluxes, and on the validation of this local scale model on a regional and national scale. In both the clusters CH 4 and N 2 O (respectively Section 3 and Section 4 ) anthropogenic and biogenic sources were studied. Major criteria to study sources were the source strength, but also the uncertainty in the source estimate and the potential emission reduction, all projected on the Dutch situation. Exception were the projects on CH 4 emission from rice fields, and the sea/air exchange of N 2 O in oceans; expertise was available in The Netherlands to carry out these studies. As in the sub-theme CO 2 the study of processes in grasslands was given a high priority in the sub themes CH 4 and N 2 O in order to quantify emission the mentioned greenhouse gases. Moreover, in the CH 4 -sub theme projects were performed to evaluate and validate the strength of various sources. The two remaining clusters (limited in extend) were aimed at the development of emission databases and geographic quantification of soil processes controlling greenhouse gas fluxes (cluster Database Development, Section 5 ), and on national inventories (cluster Socio-economic Causes, Section 6 ). In the framework of the first cluster two databases were developed, one was the World Inventory of Soil Emission potentials (WISE), a global gridded database of the primary soil factors controlling soil greenhouse gas emissions, and the other was Emission Database for Global Atmospheric Research (EDGAR) aimed to describe the processes as land use, energy consumption etc, which control the emissions of greenhouse gases and other air pollutants. The goal of the other sub theme was to develop and apply methodologies to compile national inventories of greenhouse gas emissions in The Netherlands, focused on the compounds CH 4 and N 2 O.