page_title: Exoenzyme
section_title: Bioremediation applications
hierarchical_section_title: Exoenzyme / Bioremediation applications
caption_attribution_description: English: A simplified model for MyoE function at the hyphal tip. A. A myoE+ cell. Exocytic vesicles move along microtubules powered by kinesin molecules. (It is likely that several kinesins can carry out this function.) There is a large zone of overlap between microtubules and actin microfilaments. When exocytic vesicles become detached from microtubules, as will generally be the case because of the limited processivity of kinesins, MyoE, on the vesicles will move the vesicles along actin microfilaments, collecting them at the Spitzenkörper. The vesicles then fuse in a fairly small area to the plasma membrane releasing their contents and resulting in hyphal growth. MyoE, vesicle components and, probably, many more proteins are moved in retrograde direction by dynein where they will be reused. For simplicity, much of the endocytic machinery including endosomes and actin patches has been left out of this model. For a more detailed model of the endocytic machinery please see reference 10. doi:10.1371/journal.pone.0031218.g009A
context_page_description: An exoenzyme, or extracellular enzyme, is an enzyme that is secreted by a cell and functions outside that cell. Exoenzymes are produced by both prokaryotic and eukaryotic cells and have been shown to be a crucial component of many biological processes. Most often these enzymes are involved in the breakdown of larger macromolecules. The breakdown of these larger macromolecules is critical for allowing their constituents to pass through the cell membrane and enter into the cell. For humans and other complex organisms, this process is best characterized by the digestive system which breaks down solid food via exoenzymes. The small molecules, generated by the exoenzyme activity, enter into cells and are utilized for various cellular functions. Bacteria and fungi also produce exoenzymes to digest nutrients in their environment, and these organisms can be used to conduct laboratory assays to identify the presence and function of such exoenzymes. Some pathogenic species also use exoenzymes as virulence factors to assist in the spread of these disease-causing microorganisms.
context_section_description: Bioremediation is a process in which pollutants or contaminants in the environment are removed through the use of biological organisms or their products. The removal of these often hazardous pollutants is mostly carried out by naturally occurring or purposely introduced microorganisms that are capable of breaking down or absorbing the desired pollutant. The types of pollutants that are often the targets of bioremediation strategies are petroleum products (including oil and solvents) and pesticides. In addition to the microorganisms ability to digest and absorb the pollutants, their secreted exoenzymes play an important role in many bioremediation strategies.
  Fungi have been shown to be viable organisms to conduct bioremediation and have been used to aid in the decontamination of a number of pollutants including polycyclic aromatic hydrocarbons (PAHs), pesticides, synthetic dyes, chlorophenols, explosives, crude oil, and many others. While fungi can breakdown many of these contaminants intracellularly, they also secrete numerous oxidative exoenzymes that work extracellularly. One critical aspect of fungi in regards to bioremediation is that they secrete these oxidative exoenzymes from their ever elongating hyphal tips. Laccases are an important oxidative enzyme that fungi secrete and use oxygen to oxidize many pollutants. Some of the pollutants that laccases have been used to treat include dye-containing effluents from the textile industry, wastewater pollutants (chlorophenols, PAHs, etc.), and sulfur-containing compounds from coal processing.
  Bacteria are also a viable source of exoenzymes capable to facilitating the bioremediation of the environment. There are many examples of the use of bacteria for this purpose and their exoenzymes encompass many different classes of bacterial enzymes. Of particular interest in this field are bacterial hydrolases as they have an intrinsic low substrate specificity and can be used for numerous pollutants including solid wastes. Plastic wastes including polyurethanes are particularly hard to degrade, but an exoenzyme has been identified in a Gram-negative bacterium, Comamonas acidovorans, that was capable of degrading polyurethane waste in the environment. Cell-free use of microbial exoenzymes as agents of bioremediation is also possible although their activity is often not as robust and introducing the enzymes into certain environments such as soil has been challenging. In addition to terrestrial based microorganisms, marine based bacteria and their exoenzymes show potential as candidates in the field of bioremediation. Marine based bacteria have been utilized in the removal of heavy metals, petroleum/diesel degradation and in the removal of polyaromatic hydrocarbons among others.
caption: Exocytic vesicles move along actin microfilaments toward the fungal hyphal tip where they release their contents including exoenzymes
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