Is Genetic Engineering a Route to Enhance Microalgae-Mediated Bioremediation of Heavy Metal-Containing Effluents?

Abstract

Contamination of the biosphere by heavy metals has been rising, due to accelerated anthropogenic activities, and is nowadays, a matter of serious global concern. Removal of such inorganic pollutants from aquatic environments via biological processes has earned great popularity, for its cost-effectiveness and high efficiency, compared to conventional physicochemical methods. Among candidate organisms, microalgae offer several competitive advantages; phycoremediation has even been claimed as the next generation of wastewater treatment technologies. Furthermore, integration of microalgae-mediated wastewater treatment and bioenergy production adds favorably to the economic feasibility of the former process—with energy security coming along with environmental sustainability. However, poor biomass productivity under abiotic stress conditions has hindered the large-scale deployment of microalgae. Recent advances encompassing molecular tools for genome editing, together with the advent of multiomics technologies and computational approaches, have permitted the design of tailor-made microalgal cell factories, which encompass multiple beneficial traits, while circumventing those associated with the bioaccumulation of unfavorable chemicals. Previous studies unfolded several routes through which genetic engineering-mediated improvements appear feasible (encompassing sequestration/uptake capacity and specificity for heavy metals); they can be categorized as metal transportation, chelation, or biotransformation, with regulation of metal- and oxidative stress response, as well as cell surface engineering playing a crucial role therein. This review covers the state-of-the-art metal stress mitigation mechanisms prevalent in microalgae, and discusses putative and tested metabolic engineering approaches, aimed at further improvement of those biological processes. Finally, current research gaps and future prospects arising from use of transgenic microalgae for heavy metal phycoremediation are reviewed.

Genetic engineering to enhance microalgal-based produced water treatment with emphasis on CRISPR/Cas9: A review

“…Additionally, genome-editing techniques can be very expensive and involve complex procedures with some technical challenges, such as TALEN (Khan, 2019). Furthermore, in order to manipulate the genome of microalgae to improve its removal of a specific contaminant, such as heavy metals, a complete understanding of the cells' metabolism and structure during metal stress is required to ensure the maximum effectiveness of those engineered cells for bioremediation (Ranjbar and Malcata, 2022).…”

A potential paradigm in CRISPR/Cas systems delivery: at the crossroad of microalgal gene editing and algal-mediated nanoparticles

“…Microalgae have a variety of appealing advantages, but there are still several obstacles existing which are high turbidity, contamination by other microbes, and difficulties in harvesting microalgae biomass. These issues can be resolved using the methods including genomics, computational biology, proteomics, bioinformatics, molecular modelling, molecular dynamics simulation, and a specialised algorithm for pathways prediction [ 305 ]. These combined approaches may provide a fast understanding of pollutant binding, degradation, and absorption [ 306 ].…”

Multiomics approaches and genetic engineering of metabolism for improved biorefinery and wastewater treatment in microalgae

“…[ 186 ] Through omics analysis and genetic modification, the cellular and molecular mechanisms associated to microalgae‐mediated adsorption, intake, accumulation, and transformation of heavy metals, the most promising genetic and metabolic engineering targets are proposed at improving the bioremediation capacity of microalgae from heavy metal‐containing wastewaters via the state‐of‐art molecular and bioinformatic tools. [ 175 ] Recently, the genomics analysis of three Chlorella isolates that can remove antibiotics gives new insights for the metabolic engineering of microalgae with improved antibiotic removal ability. [ 187 ] Comparative genomic analysis of a Chlorella strain that shows best WWT ability with other two strains provides fundamental information to unveil the molecular basis of abiotic stress tolerance in WWT, which is essential for future genetic engineering of strain suitable for swine WWT.…”

“…[172,173] Advances in multiomics techniques in combination of metagenomics analysis provide great help in unlocking microalgal cell metabolism and physiology to promote sustainable WWT for generation of microalgal feedstock and reclamation of water for various purposes (Figure 3). [160,174,175] At present, the efficiency of WWT by microalgae is dependent on their associated microbes (bacteria) community, for which the multiomics techniques of microalgae-bacterial consortia are being intensively studied in recent years. [176] Biological treatment by microalgae and their associations with microbial communities supported by providing oxygen for the bacterial breakdown of organic materials and to sequester N and P into biomass for water cleanup as phytoremediation provides a newfangled eco-friendly and costeffective WWT protocol.…”

“…[183] Novel biotechnological approaches regarding genome modification of microalgal cells to improve pollutant removal properties, resistance to adverse wastewater environments, and biomass and desired metabolite productivity for elevated performance of microalgae-based WWT have been emerged. [175] At present, physiology manipulation through process engineering can be adopted to stimulate activities of microalgae related to the degradation of pollutants by optimizing environmental conditions. For example, an increase in light intensities results in higher biomass production and fatty acid contents of Desmodesmus sp.…”