Trends in Biotechnology
ReviewNew Prospects for Modified Algae in Heavy Metal Adsorption
Section snippets
Heavy Metals: Pollution, Health Effects, and Remediation
Heavy metal pollution poses serious health risks to living organisms and leads to deterioration of environmental quality as a result of the high toxicity of heavy metals (see Glossary) combined with their nonbiodegradability and ability to bioaccumulate in living organisms and the food chain. Various industries directly or indirectly release heavy metals in liquid waste effluent into rivers or the sea, which has resulted in increasing public concern. In light of this issue, the World Health
Biological and Molecular Approaches
Genetic engineering has recently become a subject of close scrutiny in the field because it allows algae to be fine-tuned to improve their selectivity and adsorption capacity. Algal genetic engineering has been explored since the end of the 1970s in the model system of the cyanobacterium (blue-green alga) Synechococcus sp. 7002, which was transformed by introducing exogenous homologous DNA carrying a selectable marker.
The exceptional tolerance of algae to elevated heavy metal concentrations has
Chemical Approaches
In the biosorption process, the algal cell wall is the first barrier encountered by heavy metals, and the constituents of the cell wall determine the mechanism of heavy metal sequestration. For example, a typical algal cell wall consists of a cellulose skeleton in the form of xylans or mannans as well as an amorphous embedding matrix that is typically composed of alginate, alginic acid, and sulfated galactans. The functional groups of polysaccharides and lipids that contribute to the adsorption
Alginate Extraction Approach
The role of alginate in adsorption has been demonstrated by Bertagnolli and colleagues [49] who reported a 36.1% decrease in Cr(VI) adsorption capacity after alginate has been extracted from Sargassum filipendula. Although alginate is deemed to be the main component responsible for algal heavy metal binding, it is also an important resource for food, textile, and pharmaceutical products. Nevertheless, alginate extraction residues may still have metal-binding properties because of the remaining
Nanoparticle Synthesis Approach
One emerging technique in algal heavy metal adsorption is the synthesis of NPs from algal biomass. The field of NP synthesis is growing rapidly, fueled by breakthroughs in different synthesis mechanisms and the prospect of unique applications owing to their outstanding properties. These fascinating properties of NPs are due to their small sizes, and thus a high surface area to volume ratio, and superior reactivity versus their bulk counterparts [53]. Synthesis of metal NPs mediated by algae is
Future Challenges and Opportunities
The aforementioned approaches to enhance algal heavy metal adsorption capacity and selectivity have inherent prospects and bottlenecks. Algae show extraordinary potential for metal biosorption owing to their abundance and programmable photoautotrophy for genetic design and construction [26]. Genetic engineering by expressing metalloregulatory proteins can be applied to selectively adsorb heavy metals because different types of proteins differ in their affinities for specific heavy metals. In
Concluding Remarks
This comprehensive review presents an updated account of emerging approaches to enhance algal heavy metal biosorption capacity and selectivity. Biological modifications have created a paradigm shift in algal biosorption because they allow the algae to be designed to express specific binding proteins at their surfaces to adsorb targeted metal species. However, compared with other microorganisms such as bacteria and yeast, genetic engineering of algae is still in its infancy, and there is a need
Acknowledgements
Our research is supported by the Malaysia Ministry of Education (TR001A-2015A) and the University of Malaya (RP025B-SUS18). The authors gratefully acknowledge the financial support received from Taiwan’s Ministry of Science and Technology (MOST) under grant numbers 108-3116-F-006-007-CC1, 107-2221-E-006-112-MY3, and 107-2621-M-006-003.
Glossary
- Alginate extract
- an alginate salt extract of algae, usually in the form of soluble sodium alginate or the precipitate of sodium alginate solution either from alginic acid or calcium alginate.
- Alginate extract residue
- algal cell biomass produced in the alginate extraction process. After alginate extraction, the biomass contains many of the constituents of the raw algae, and thus has potential for heavy metal adsorption.
- Biochar
- carbonized biomass obtained from biological resources.
- Biosorption
- a
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