Naturally occurring bioremediators will emerge at a polluted site over time, thanks to the adaptability and diversity of microbial ecology. Humans can encourage this process through biostimulation. Biostimulation involves aerating (i.e., bioventing) or adding nutrients to a site to encourage the growth of indigenous bioremediating microbes (Mrozik and Piotrowska-Seget 2010). Bioaugmentation13 goes a step further, by intentionally inoculating contaminated sites with cultured bacteria (Mrozik and Piotrowska-Seget 2010). Bioaugmentation with bacterial consortia may be more effective than with single strains, as microbial communities often take a tag-team approach to environmental cleanup: the by-product of one microbe is the food for another, and so on. Bioremediators may have been isolated from a similarly polluted site in the past or genetically engineered to “eat” environmental contaminants. Traditionally, genetically engineered bioremediation has been relatively simple, involving the horizontal transfer of whole plasmids from environmental isolates to more desirable bacterial strains (Mrozik and Piotrowska-Seget 2010). In some cases, natural bioremediators are used to construct bioreporter strains, thus allowing for coupled detection and cleanup (Xu et al. 2013). More recently, researchers have explored customized degradation through the

mixing and matching of catabolic genes from various sources. Tools and biological reference sequences from the ‘omics, synthetic biology, and bioinformatics facilitate this work.

In situ bioaugmentation can be enhanced and controlled through the use of cell immobilization strategies. Introduced cells are contained by adsorption to a surface, entrapment by an ion-exchange permeable biocarrier, or encapsulization by an inert and semi-permeable material14 (Mrozik 2010; Bayat, Hassanshahian, and Cappello 2015). These strategies offer more controlled growth conditions (i.e., pH, temperature) while discouraging the environmental dispersal of bioremediators.

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