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
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K. N. Timmis (ed.), Handbook of Hydrocarbon and Lipid Microbiology, DOI 10.1007/978-3-540-77587-4_99, # Springer-Verlag Berlin Heidelberg, 2010
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Water-Hydrophobic Compound Interactions with the Microbial Cell
Abstract: 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 Poctanol-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.
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Introduction
The microbial cell is a fragile aqueous system, and dissolved substances represent potentially lethal challenges to its macromolecular structures. Microbes in Nature are exposed to an indefinite number of extracellular compounds (see > Vol. 1, Part 3), some of which will penetrate the cellular membrane. These may be utilized for metabolic purposes (e.g., for signaling; as nutrients used during structural growth or to synthesize compatible solutes), may act as toxicants that inhibit metabolism via a site-specific mode-of-action (see > Vol. 2, Part 8), and/or may induce cellular stress via physicochemical interventions in macromolecular structures and their interactions. The ecology of a microbial species, as well as its evolutionary trajectory, are determined by its ability to survive, respond, and adapt to environmental challenges, the most powerful of which are those that induce diverse forms of water stress (Brown, 1990; Hallsworth et al., 2007; Kashangura et al., 2006). All dissolved substances, even stress protectants, can act as cellular stressors that reduce water activity, induce osmotic or matric stress, impair the functionality of lipid bilayers and/or exert chaotropic activity towards biological macromolecules (Brown, 1990; Duda et al., 2004; Ferro Fonta´n and Chirife, 1981; Hallsworth and Magan, 1994; Hallsworth, 1998; Hallsworth et al., 2003, 200
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