Water-Hydrophobic Compound Interactions with the Microbial Cell
The structural interactions of biological macromolecules, their biochemical activities and, ultimately, the metabolic function of cellular systems are dependent upon weak inter- and intra-molecular forces such as hydrogen bonds, Van der Waals forces, and the hydrophobic effect. Water molecules, and those of hydrophobic substances such as hydrocarbons, can take part in and/or modify these interactions and thereby determine the operational and structural stability of the microbial cell and its macromolecular systems. We explain how the cytosol, plasma membrane and the extracellular solution form a material and energetic continuum; and discuss the behavior of hydrophobic substances of extracellular origin as they migrate into the plasma membrane and into the cell's interior. The adverse effects of substances with a log P octanol-water ≥2, that partition into the hydrophobic domains of biological macromolecules, are discussed in relation to microbial cell function; and we speculate whether the cellular stress that they induce is symmetrical or asymmetrical in nature. In the context of the microbial environment, we take a situational-functional approach to consider how hydrophobic stressors interact with the microbial cell, and what types of evasion tactics microbes can employ to minimize their inhibitory activities. Finally, we discuss the ecological implications of hydrocarbon-induced cellular stress for microbial systems.
We are grateful for thought-provoking discussions with Giuseppe Albano (Edinburgh University, UK), Prashanth Bhaganna and Kalpa D. Gupta (Queen’s University Belfast, Northern Ireland), Ananda Hillis (University of Ulster, UK), Allen Y. Mswaka (University of Harare, Zimbabwe), Mary Palfreyman (Outwood Grange College, UK), Harald J. Ruijssenaars (TNO Quality of Life, The Netherlands), Kenneth N. Timmis (HZI, Germany) and Graham J. C. Underwood (University of Essex, UK). Work on this article was funded by the Kluyver Centre for Genomics of Industrial Fermentation (The Netherlands), EU Fifth-Framework contract QLK3-CT-2002-01933 (LINDANE), Biotechnology and Biological Sciences Research Council (BBSRC, UK) and Natural Environment Research Council (NERC, UK).
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