A study on microalgal bioremediation of emerging contaminants with transcriptomics approach

Abstract

Contamination of natural reservoirs by industrial processes and other human activities restricts access to water utilization. The presence of emerging contaminants (ECs) in water poses potential environmental threats, necessitating the exploration of sustainable technologies for effectively removing ECs as well as organic and inorganic pollutants. Freshwater microalgae, an integral part of freshwater ecosystems, exhibit the ability to utilize these contaminants as nutrients, presenting them as potential candidates for mitigating and controlling these environmental pollutants. Therefore, investigating the bioremediation capability of freshwater microalgae for ECs represents a pivotal step towards adopting a sustainable approach to minimize the pollutant load on aquatic ecosystems. In this study, we have investigated four species of freshwater microalgae (Chlorella sorokiniana, Chlamydomonas mexicana, Scenedesmus obliquus, and Chlorella vulgaris) as potential candidates for efficient bioremediation of two ECs: bisphenol AP (BPAP) and sulfacetamide (SA), representing an endocrine disruptor and an antibiotic, respectively. These microalgae were selected based on their known tolerance to contaminants and efficiency in pollutant removal. The BPAP revealed to be toxic to microalgae, with 120hr- EC50 of BPAP for microalgal species ranged from 1.509 mg L−1 to 6.509 mg L−1. Over a twelve-day treatment period, microalgae exhibited 56.5% – 86.5% removal of 1 mg L-1 BPAP, with C. mexicana emerging as the most promising candidate. The metabolomic analysis revealed the successful biotransformation of BPAP into less toxic molecules by C. mexicana. Transcriptomics analysis illuminates the molecular responses of C. mexicana to BPAP with an upregulation of adenylyltransferase, farnesyltransferase, glycosyltransferase, dehydrogenases, sulfurtransferase and methyltransferase encoding genes. In the other study, S. obliquus exhibited a considerable bioremediation potential for SA. S. obliquus successfully removed 16.8% of 15 mg L-1 SA over 14 days. A notable increase to 18.8% was obtained with a 50 mg L-1 Al2O3NP co-treatment under the same experimental conditions. This underscores an enhanced SA biodegradation capacity of S. obliquus in the presence of Al2O3NP. The metabolic analysis confirmed the biotransformation of SA into simple, less toxic molecules. The transcriptomics analysis of S. obliquus highlighted the molecular responses to SA and Al2O3NP exposure. Genes responsible for ATP synthesis and the photosynthetic system in S. obliquus were significantly downregulated, while the oxidoreductase gene of the pivotal biodegradation enzyme exhibited significant upregulation. The successful bioremediation by freshwater microalgal species positions them as promising candidates for sustainable bioremediation of ECs. Furthermore, the study not only substantiates the efficacy of microalgae in mitigating BPAP and SA but also delves into the intricate dynamics of the biotransformation mechanism and their regulation.