Importance of bioremediation and its future prospects

Bioremediation helps clean up polluted environments, including soils, groundwater, and marine environments. Such systems can include bacteria, fungi, algae, and plant species. They are capable of metabolizing, immobilizing, or absorbing toxic compounds from their environment. However, a major advantage of these systems is that they are less harmful to the environment with minimum or no by-products. Moreover, conventional physical and chemical treatments are expensive and inefficient and cause more harm than good. Thus, by evaluating research undertaken in bioremediation so far. More efficient and feasible bioreactors or products may be designed. Furthermore, these systems could be capable of completely removing pollutants from the environment. Also, it leads to useful compounds as by-products.

Microbes are an efficient tool for bioremediation technology

A common theme recurring in bioremediation studies is that majority of the species that have been discovered with remediating properties are capable of natural attenuation. However, researchers have adopted these species capable of naturally degrading contaminants (for example bioreactors). On the other hand, these organisms have also been selected naturally for bioremediation capabilities, when high concentrations of specific compounds have been introduced in their environment.

On the other hand, naturally selected species have found specific importance in oil and plastic bioremediation fields, evident from the vast body of research from Exxon Valdez and Deepwater Horizon oil spills. Furthermore, other equally important examples include mitigating heavy metal pollution (soil, aquatic and marine systems) as a result of industrialization, such as lead, chromium, mercury, and arsenic. Similarly, unique cases of industrial pollution that require bioremediation assistance include radioactive metal, Uranium, and also groups of recalcitrant by-products of pharmaceutical and textile manufacturing industries. In addition, studies of these naturally selected species can be advantageous in designing more efficient biological systems by isolating, modifying, and introducing unique genes in model organisms.

Functions of microbial bioremediation

Under this project, the diversity of microbes involved in the bioremediation of specific pollutants has been studied and their modes of actions reviewed. However, irrespective of the cellular compounds involved, microbes achieve bioremediation through one or more of the following:

• Biosorption
• Complexation
• Bioassimilation
• Enzymatic transformation
• Mineralization

These common pathways guide researchers in designing bioreactors for the efficient removal of pollutants.  Also, enzymes and biofilms have consistently shown importance in bioremediation processes, no matter the pollutant type. While enzymes have been argued to be highly efficient in bioremediation, their cost of purification and stability issues have limited researchers in developing practical applications for the molecules.

The application of these microbes in a real-time remediation system or bioreactor is far from being possible. On the other hand, researchers have designed, tested, and implemented several lab-scale bioreactors (Firmino et al., 2015; Hossain et al., 2015). However, the actual application of such systems on a wide scale is rare. This suggests that there are issues with the upscaling and logistics of big operations.

One successful example of applying bioremediation in large-scale cleanup is the Mumbai oil spill of 2010, when ‘oilzapper’; a patented microbial consortium capable of degrading oil was applied to the polluted beach, with successful outcomes (Maharashtra Pollution Control Board, 2010). However, in the case of the Deepwater Horizon spill, bioremediation operations were not possible, but policymakers relied on natural bioremediation processes to mitigate the disaster (Atlas & Hazen, 2011).

Emerging trends in bioremediation

Subsequently, the future of bioremediation as a technology depends on understanding the drivers (biotic and abiotic) influencing the natural selection of organisms capable of metabolizing pollutants. Moreover, information on the underlying genomes and proteasomes involved in bioremediation will also contribute towards designing efficient bioremediation systems. On the other hand, analysis of relevant genomic and proteomic sequences, their diversity, and also evolutionary relationships existing between them can contribute towards designing efficient bioremediation systems. However, sequence information can help in studying functional variations of different variants of important genes and proteins existing in nature. Such information could further help design more efficient proteins of microbes or whole systems. Also, systems biology information like molecular pathways and interactions existing within the cell and outside (in biofuels for example) can shine the light on the secondary factors influencing the central bioremediation processes.

Instances of microbial bioremediation

Knowledge of these factors will help predict the behaviours of organisms under different conditions of bioremediation, as argued by Jafari, Danesh, & Ghoosta, (2013). However, existing research has determined sequences and structural information of cellular components involved in bioremediation, but extensive research is still lacking in their diversity and modification for higher efficiency products.

Apart from the removal of pollutants, the end-products or by-products are also important in the remediation system (Jonsson & Haller, 2014; Tripathi, Edrisi, O’Donovan, Gupta, & Abhilash, 2016). Typically researchers look for either less toxic forms of pollutants or complete mineralization of the initial pollutant. However, the next generation of bioremediation protocols will focus on synthesizing useful-by products that could be consumed by humans. The figure below shows the major useful by-products that researchers target in designing remediation systems, focusing mainly on energy.

For example, research however attempts to efficiently convert the chemical energy stored in wastewater to electricity through the production of electrons during metabolic activities (Jadhav, Ghosh, & Ghangrekar, 2017).

Similarly, research conducted in coupling bioremediation with biofuel production, using bacteria and microalgae helped turn waste into biofuel  (Thomas et al., 2016; Waghmare, Kadam, Saratale, & Govindwar, 2014).

Future scope

Furthermore, research will explore the role of phytoremediation in mediating environmental pollution. Moreover, phytoremediation is advantageous over microbial remediation considering their economic feasibility, widespread pollution degradation capacity, higher public acceptance, and also a high rate of contaminant reduction or degradation (Tangahu et al., 2011).

Therefore, bioinformatics and biostatistics analyses conducted on phytoremediation data will help evaluate and justify the need for genetically modified organisms. Henceforth, GMO plants will possess previously identified efficient metabolic processes, enzymes, genes, or operons capable of bioremediation specific pollutants. However, genomics, proteomics, and metabolomics concerned with bioremediation help to explore in devising possible solutions targeting specific pollutants. Subsequently, the following areas under bioremediation will be explored:

1. Identification and comparison of gene and protein sequences capable of efficient removal of contaminants.
2. Diversity and Phylogenetic studies of important gene and protein sequences involved in bioremediation processes.
3. Application of important genes in plant biotechnology.

GMO plants are capable of remediation of a wide range of waste effluents and polluted lands can be advantageous and also be a potential candidate for practical applications.

References

• Atlas, R. M., & Hazen, T. C. (2011). Oil biodegradation and bioremediation: a tale of the two worst spills in U.S. history. Environmental Science & Technology, 45(16), 6709–6715. http://doi.org/10.1021/es2013227.
• Firmino, P., Farias, R., Barros, A., Buarque, P., Rodriguez, E., Lopes, A., & do Santos, A. (2015). Understanding the anaerobic BTEX removal in continuous-flow bioreactors for ex situ bioremediation purposes. Chemical Engineering, 281(2015), 272–280. Retrieved from http://www.sciencedirect.com/science/article/pii/S1385894715009468.
• Hossain, K., Ismail, N., Rafatullah, M., Quaik, S., Nasir, M., Maruthi, A., & Shaik, R. (2015). Bioremediation of textile effluent with membrane bioreactor using the white-rot fungus Coriolus versicolor. Journal of Pure and Applied Microbiology, 1(9), 1979–87. Retrieved from http://go.galegroup.com/ps/i.do?p=AONE&sw=w&issn=09737510&v=2.1&it=r&id=GALE%7CA436439688&sid=googleScholar&linkaccess=fulltext.
• Jadhav, D., Ghosh, R. S., & Ghangrekar, M. (2017). Third generation in bio-electrochemical system research – A systematic review on mechanisms for recovery of valuable by-products from wastewater. Renewable and Sustainable Energy Reviews, 76, 1022–1031.
• Jafari, M., Danesh, Y. R., & Ghoosta, Y. (2013). Molecular techniques in fungal bioremediation. In Fungi as Bioremediators (pp. 453–465). Springer Berlin Heidelberg.
• Jonsson, A., & Haller, H. (2014). Sustainability Aspects of In-Situ Bio-remediation of Polluted Soil in Developing Countries and Remote Regions. In Environmental Risk Assessment of Soil Contamination. InTech. http://doi.org/10.5772/57315.
• Maharashtra Pollution Control Board. (2010). Report on Oil Spill in Arbian Sea. Mumbai. Retrieved from http://mpcb.gov.in/images/pdf/Report_Oil Spill_ Arbian Sea.pdf.
• Tangahu, B. V, Abdullah, A. R. S., Basri, H., Idris, M., Anuar, N., & Mukhlisin, M. (2011). A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants through Phytoremediation. International Journal of Chemical Engineering, 2011, 31. https://doi.org/10.1155/2011/939161.
• Thomas, D. G., Minj, N., Mohan, N., Rao, P. H., Thomas, D. G., & Minj, N. (2016). Cultivation of Microalgae in Domestic Wastewater for Biofuel Applications – An Upstream Approach. Journal of Algal Biomass Utilization, 7(1), 62–70.
• Tripathi, V., Edrisi, S. A., O’Donovan, A., Gupta, V. K., & Abhilash, P. C. (2016). Bio-remediation for Fueling the Biobased Economy. Trends in Biotechnology. http://doi.org/10.1016/j.tibtech.2016.06.010.
• Waghmare, P. R., Kadam, A. A., Saratale, G. D., & Govindwar, S. P. (2014). Enzymatic hydrolysis and characterization of waste lignocellulosic biomass produced after dye bio-remediation under solid state fermentation. Bioresource Technology, 168(2014), 136–141. http://doi.org/10.1016/j.biortech.2014.02.099.