Extracellular exudates

Microbes are ubiquitous in the subsurface environment and as such may play an important role in groundwater solute behavior. Microbes in the subsurface can influence pollutants by solubility enhancement, precipitation, or transformation (biodegradation) of the pollutant species. Microbes in the groundwater can act as colloids or participate in the processes of colloid formation. Bacterial attachment to granular media can be reversible or irreversible and it has been suggested that extracellular enzymes are present in the system. Extracellular exudates (slimes) can be sloughed-off and act to transport sorbed materials [122]. The stimulation of bacterial growth in the subsurface maybe considered as in situ formation of colloids. 

Some is released into seawater as an extracellular exudate or as a result of viral lysis and from sloppy feeding by the grazers. Consumption by grazers entrains the organic matter in the marine food web as shown in Figure 23.2. Cells that are not consumed or lysed by a virus can sink or be otherwise carried out of the euphotic zone by currents. 

Gums and mucilages may be found either in the intracellular pans of plants or as extracellular exudates. Those found within plant cells represent storage material in seeds and roots. They also serve as a water reservoir and as protection for germinating seed. The polysaccharides found as extracellular exudates of higher plants appear to be produced as a result of injury caused by mechanical means or by insects. It has not been well established whether the exudates are formed at the site of the injury. 

Williams, D.E (1994) Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effect on biocompatibility, in-vivo. Biomaterials. 15, 779-785. 

In some cases, exudates enable the plankton to control their environment. For example, diatoms release compounds, called oxyUpins, that induce natural abortions and growth reduction in the zooplankton that are their primary predators. Other exudates complex with trace metals, serving to reduce the bioavailability of toxics, such as copper, and enhance the bioavailability of micronutrients, such as iron. Examples of iron-binding extracellular DOM are the siderophores (Figure 5.11). 

An alternative approach for screening the composition of phytoplankton exudates is to use either 14C-tracer methods combined with chemical fractionation (Hama and Handa, 1987 Siuda and Wcisko, 1990 Sundh, 1991) or colorimetric methods (Obernosterer and Herndl, 1995 Biddanda and Benner, 1997) to characterize the contribution of different classes of organic compounds (carbohydrates and amino acids in polymeric or monomeric forms) to the total pool of exudates. These studies revealed that monomeric and combined carbohydrates were the major components of exudates, typically accounting for 20-90% of the total extracellularly released DOM. 

Natural gums include plant exudates, seed gums, plant extracts, seaweed extracts, and the extracellular microbial polysaccharides. Plant exudates include gum arabic, gum ghatti, gum karaya, and gum tragacanth. Seed gums include... 

Extending this idea one step further, bacteria may have evolved to produce extracellular polymeric substances (EPSs) in order to make mineral surfaces more favorable for attachment. This would be an important evolutionary step, especially if the earliest bacteria utilized minerals for respiration and nutrition.25 According to the present model, oxides other than quartz also have unfavorable entropic interactions with the head group PL (AS°adsi < 0). EPSs should then be exuded on the surfaces of many oxide (and silicate) minerals. As discussed above, quartz is the most harmful, so greater production of EPSs should be expected on quartz, all other factors being equal. Consistent with this hypothesis, the nature of the substrate and of the bacterial surfaces does, in fact, affect the amount of EPS produced.60-62 The idea that surfaces become more hydrophilic by bacterial attachment also underlies the biobeneflciation of ores during mineral separation by floatation. 

VEGF Trap Fusion protein, of extracellular domains of VEGFR-1 and -2 fused to the Ec portion of IgGl Regeneron Pharmaceuticals Phase I/II Exudative AMD Intravitreal injection... 

Malinowski, D. P., Zuo, H., Beleski, D. P., and Alloush. G. A. (2004). Evidence for copper binding by extracellular root exudates of tall fescue but not perennial ryegrass infected with Neotyphodium spp. Endophytes. Plant Soil 267. 1-12. 

Corticosteroids have antiangiogenic, antifibrotic, and antipermeability properties. The principle effects of steroids are stabilization of the blood-retinal barrier, resorption of exudation, and downregulation of inflammatory stimuli. Antiangiogenesis is a secondary effect felt to be mediated primarily by upregulation of extracellular matrix protein plasminogen activator inhibitor-1 (PAI-1) in vascular endothelial cells (18). This inhibits activation of plasmin and alters extracellular matrix degradation. 

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