Biodegradation of petroleum hydrocarbons in marine and freshwater

Biodegradation of petroleum hydrocarbons in marine and freshwater environments is constrained by the ability of microorganisms to access the hydrophobic surfaces of oil droplets. A key process for attachment to oil droplets involves the production of surface active agents (Horowitz et al., 1975), which is further accompanied by changes in the properties of the cell envelope. One of the most notable features is the formation of canals in the cell wall, which appears to enable the

transport of nanometer-sized droplets into the surface of the interior cell membrane (Southam et al., 2001). The first step involving the secretion of surface active agents includes the production of relatively low-molecular-weight

surfactants that decrease the surface tension and excretion of Doramapimod high-molecular-weight polysaccharide polymers that serve to emulsify the oil and water into small particles that provide increased surface area for enzymatic attack. In several studies, these exopolymers appear along with fibrils and wall appendages (Marin et al., 1996; Macedo et al., 2005), and can include embedded flagella that are used for both motility and attachment of the cells to the oil surface (Marin et al., 1996). Another microscopic study further reports the appearance of cellular aggregates that form over the surface ICG-001 price of oil droplets and invade the oil as the biofilm matures (Macedo et al., 2005). Altogether, these studies provide the basis for comparisons of different model systems. On the other hand, there have been Florfenicol few comparative studies examining different microorganism and substrate conditions using the same methods. Moreover, the three-dimensional (3D)

structures of the microhabitats that are generated by exocellular polymers have not yet been described using 3D reconstructions of serial sections cut through oil droplets that are colonized by microorganisms. With the current interest in the remediation of oil-polluted marine and freshwater environments, a better description of the feeding structures is highly relevant for understanding how biophysical processes and cell wall adaptations influence the rate of oil degradation. The research described here used a combination of cytochemical stains and microscopy techniques to describe the specific exocellular fibrils, films and internal granules that are generated by yeasts and bacteria during oil droplet colonization. A novel aspect of the present research was the use of serial sections and computer imaging to generate a 3D reconstruction of the habitat that is formed by selected yeast and bacteria on the oil droplet surfaces. These trophic structures appear as pits and cavities that enclose microbial cells along with the polymers and enzymes that are produced by the oil-degrading microorganisms.

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