"Rational" management of dichlorophenols biodegradation by the microalga Scenedesmus obliquus

Efficiency, mechanism, influencing factors, and integrated technology of biodegradation for aromatic compounds by microalgae: A review

Aromatic compounds have received widespread attention because of their threat to ecosystem and human health. However, traditional physical and chemical methods are criticized due to secondary pollution and high cost. As a result of ecological security and the ability of carbon sequestration, biodegradation approach based on microalgae has emerged as a promising alternative treatment for aromatic pollutants. In light of the current researches, the degradation efficiency of BTEX (benzene, toluene, ethylbenzene, and xylene), polycyclic aromatic hydrocarbons (PAHs), and phenolic compounds by microalgae was reviewed in this study. We summarized the degradation pathways and metabolites of p-xylene, benzo [a]pyrene, fluorene, phenol, bisphenol A, and nonylphenol by microalgae. The influence factors on the degradation of aromatic compounds by microalgae were also discussed. The integrated technologies based on microalgae for degradation of aromatic compounds were reviewed. Finally, this study discussed the limitations and future research needs of the degradation of these compounds by microalgae.

Microalgae-based removal of pollutants from wastewaters: Occurrence, toxicity and circular economy

The natural and anthropogenic sources of water bodies are contaminated with diverse categories of pollutants such as antibiotics, pharmaceuticals, pesticides, heavy metals, organic compounds, and other industrial chemicals. Depending on the type and the origin of the pollutants, the degree of contamination can be categorized into lower to higher concentrations. Therefore, the removal of hazardous chemicals from the environment is an important aspect. The physical, chemical and biological approaches have been developed and implemented to treat wastewaters. The microbial and algal treatment methods have emerged as a growing field due to their eco-friendly and sustainable approach. Particularly, microalgae emerged as a potential organism for the treatment of contaminated water bodies. The microalgae of the genera Chlorella, Anabaena, Ankistrodesmus, Aphanizomenon, Arthrospira, Botryococcus, Chlamydomonas, Chlorogloeopsis, Dunaliella, Haematococcus, Isochrysis, Nannochloropsis, Porphyridium, Synechococcus, Scenedesmus, and Spirulina reported for the wastewater treatment and biomass production. Microalgae have the potential for adsorption, bioaccumulation, and biodegradation. The microalgal strains can mitigate the hazardous chemicals via their diverse cellular mechanisms. Applications of the microalgae strains were found to be effective for sustainable developments and circular economy due to the production of biomass with the utilization of pollutants.

Phycoremediation of phenol-polluted petro-industrial effluents and its techno-economic values as a win-win process for a green environment, sustainable energy and bioproducts

The discharge of the toxic phenol-polluted petro-industrial effluents (PPPIE) has severe environmental negative impacts, thus it is mandatory to be treated before its discharge. The objective of this review was to discuss the sustainable application of microalgae in phenols degradation, with a special emphasis on the enzymes involved in this bioprocess and the factors affecting the success of PPPIE phycoremediation. Moreover, it confers the microalgae bioenergetic strategies to degrade different forms of phenols in PPPIE. It also points out the advantages of the latest application of bacteria, fungi and microalgae as microbial consortia in phenols biodegradation. Briefly, phycoremediation of PPPIE consumes carbon dioxide emitted from petro-industries for; valorization of the polluted water to be reused and production of algal biomass which can act as a source of energy for such integrated bioprocess. Besides, the harvested algal biomass can feasibly produce; third-generation biofuels, biorefineries, bioplastics, fish and animal feed, food supplements, natural dyes, antioxidants and many other valuable products. Consequently, this review precisely confirms that the phycoremediation of PPPIE is a win-win process for a green environment and a sustainable future. Thus, to achieve the three pillars of sustainability; social, environmental and economic; it is recommendable to integrate PPPIE treatment with algal cultivation. This integrated process would overcome the problem of greenhouse gas emissions, global warming and climate change, solve the problem of water-scarce, and protect the environment from the harmful negative impacts of PPPIE.

Biodegradation of phenol by Chlamydomonas reinhardtii

The data presented in this particular study demonstrate that the biodegradation of phenol by Chlamydomonas reinhardtii is a dynamic bioenergetic process mainly affected by the production of catechol and the presence of a growth-promoting substrate in the culture medium. The study focused on the regulation of the bioenergetic equilibrium resulting from production of catechol after phenol oxidation. Catechol was identified by HPLC-UV and HPLC-ESI-MS/MS. Growth measurements revealed that phenol is a growth-limiting substrate for microalgal cultures. The Chlamydomonas cells proceed to phenol biodegradation because they require carbon reserves for maintenance of homeostasis. In the presence of acetic acid (a growth-promoting carbon source), the amount of catechol detected in the culture medium was negligible; apparently, acetic acid provides microalgae with sufficient energy reserves to further biodegrade catechol. It has been shown that when microalgae do not have sufficient energy reserves, a significant amount of catechol is released into the culture medium. Chlamydomonas reinhardtii acts as a versatile bioenergetic machine by regulating its metabolism under each particular set of growth conditions, in order to achieve an optimal balance between growth, homeostasis maintenance and biodegradation of phenol. The novel findings of this study reveal a paradigm showing how microalgal metabolic versatility can be used in the bioremediation of the environment and in potential large-scale applications.

Bioenergetic reprogramming plasticity under nitrogen depletion by the unicellular green alga Scenedesmus obliquus

Simultaneous nitrogen depletion and 3,4-dichlorophenol addition induce a bioenergetic microalgal reprogramming, through strong Cyt b ₆ f synthesis, that quench excess electrons from dichlorophenol's biodegradation to an overactivated photosynthetic electron flow and H ₂ -productivity. Cellular energy management includes "rational" planning and operation of energy production and energy consumption units. Microalgae seem to have the ability to calculate their energy reserves and select the most profitable bioenergetic pathways. Under oxygenic mixotrophic conditions, microalgae invest the exogenously supplied carbon source (glucose) to biomass increase. If 3,4-dichlorophenol is added in the culture medium, then glucose is invested more to biodegradation rather than to growth. The biodegradation yield is enhanced in nitrogen-depleted conditions, because of an increase in the starch accumulation and a delay in the establishment of oxygen-depleted conditions in a closed system. In nitrogen-depleted conditions, starch cannot be invested in PSII-dependent and PSII-independent pathways for H₂-production, mainly because of a strong decrease of the cytochrome b ₆ f complex of the photosynthetic electron flow. For this reason, it seems more profitable for the microalga under these conditions to direct the metabolism to the synthesis of lipids as cellular energy reserves. Nitrogen-depleted conditions with exogenously supplied 3,4-dichlorophenol induce reprogramming of the microalgal bioenergetic strategy. Cytochrome b ₆ f is strongly synthesized (mainly through catabolism of polyamines) to manage the electron bypass from the dichlorophenol biodegradation procedure to the photosynthetic electron flow (at the level of PQ pool) and consequently through cytochrome b ₆ f and PSI to hydrogenase and H₂-production. All the above showed that the selection of the appropriate cultivation conditions is the key for the manipulation of microalgal bioenergetic strategy that leads to different metabolic products and paves the way for a future microalgal "smart" biotechnology.

Exploring micropollutant biotransformation in three freshwater phytoplankton species

Phytoplankton constitute an important component of surface water ecosystems; however little is known about their contribution to biotransformation of organic micropollutants. To elucidate biotransformation processes, batch experiments with two cyanobacterial species (Microcystis aeruginosa and Synechococcus sp.) and one green algal species (Chlamydomonas reinhardtii) were conducted. Twenty-four micropollutants were studied, including 15 fungicides and 9 pharmaceuticals. Online solid phase extraction (SPE) coupled with liquid chromatography (LC)-high resolution tandem mass spectrometry (HRMS/MS) was used together with suspect and nontarget screening to identify transformation products (TPs). 14 TPs were identified for 9 micropollutants, formed by cytochrome P450-mediated oxidation, conjugation and methylation reactions. The observed transformation pathways included reactions likely mediated by promiscuous enzymes, such as glutamate conjugation to mefenamic acid and pterin conjugation of sulfamethoxazole. For 15 compounds, including all azole fungicides tested, no TPs were identified. Environmentally relevant concentrations of chemical stressors had no influence on the transformation types and rates.

Bioenergetic strategy of microalgae for the biodegradation of tyrosol and hydroxytyrosol

Olive mill wastewater has significant polluting properties due to its high phenolic content [mainly tyrosol (trs) and hydroxytyrosol (htrs)]. Growth kinetics and a series of fluorescence induction measurements for Scenedesmus obliquus cultures showed that microalgae can be tolerant of these phenolic compounds. Changes in the cellular energy reserves and concentration of the phenolic compounds adjust the “toxicity” of these compounds to the microalgae and are, therefore, the main parameters that affect biodegradation. Autotrophic growth conditions of microalgae and high concentrations of trs or htrs induce higher biodegradation compared with mixotrophic conditions and lower phenolic concentrations. When microalgae face trs and htrs simultaneously, biodegradation begins from htrs, the more energetically demanding compound. All these lead to the conviction that microalgae have a “rational” management of cellular energy balance. Low toxicity levels lead to higher growth and lower biodegradation, whereas higher toxicity levels lead to lower growth and higher biodegradation. The selection of appropriate conditions (compatible to the bioenergetic strategies of microalgae) seems to be the key for a successful biodegradation of a series of toxic compounds, thus paving the way for future biotechnological applications for solving complicated pollution problems, like the detoxification of olive mill wastewater.

Multi-substrate biodegradation of chlorophenols by defined microbial consortium

In the present study, a defined mixed microbial consortium was investigated for their ability to utilize three different monochlorophenols (MCPs) and 2,4-DCP individually and in the mixture. None of the individual strains were able to utilize 3-CP and 4-CP, but when they were mixed to form defined consortium, they have shown great potential and degradation of high concentration of 3-CP and 4-CP. Spectrophotometric analysis of metabolites during MCPs degradation establishes the presence of 2-chloromaleylacetate. Multi-substrate degradation study of 2,4-DCP in the presence of three MCPs showed the great prospect of microbial consortium for in situ bioremediation. During multi-substrate degradation, the biodegradation rate (mg L-1 day-1) was observed in the order of 2,4-DCP > 2CP > 3CP > 4CP. Biodegradation kinetic of three MCPs using Andrew's model showed maximum removal rate (R m) of 2.78, 0.91, 1.82 mg L-1 h-1 for 2-CP, 3-CP and 4-CP, respectively.

Biodegradation of polychlorinated biphenyls (PCBs) by the novel identified cyanobacterium Anabaena PD-1

Polychlorinated biphenyls (PCBs), a class of hazardous pollutants, are difficult to dissipate in the natural environment. In this study, a cyanobacterial strain Anabaena PD-1 showed good resistance against PCB congeners. Compared to a control group, chlorophyll a content decreased 3.7% and 11.7% when Anabaena PD-1 was exposed to 2 and 5 mg/L PCBs for 7 d. This cyanobacterial strain was capable of decomposing PCB congeners which was conclusively proved by determination of chloride ion concentrations in chlorine-free medium. After 7 d, the chloride ion concentrations in PCB-treated groups (1, 2, 5 mg/L) were 3.55, 3.05, and 2.25 mg/L, respectively. The genetic information of strain PD-1 was obtained through 16S rRNA sequencing analysis. The GenBank accession number of 16S rRNA of Anabaena PD-1 was KF201693.1. Phylogenetic tree analysis clearly indicated that Anabaena PD-1 belonged to the genus Anabaena. The degradation half-life of Aroclor 1254 by Anabaena PD-1 was 11.36 d; the total degradation rate for Aroclor 1254 was 84.4% after 25 d. Less chlorinated PCB congeners were more likely to be degraded by Anabaena PD-1 in comparison with highly chlorinated congeners. Meta- and para-chlorines in trichlorodiphenyls and tetrachlorobiphenyls were more susceptible to dechlorination than ortho-chlorines during the PCB-degradation process by Anabaena PD-1. Furthermore, Anabaena PD-1 can decompose dioxin-like PCBs. The percent biodegradation of 12 dioxin-like PCBs by strain PD-1 ranged from 37.4% to 68.4% after 25 days. Results above demonstrate that Anabaena PD-1 is a PCB-degrader with great potential for the in situ bioremediation of PCB-contaminated paddy soils.

Lichen symbiosis: nature's high yielding machines for induced hydrogen production

Hydrogen is a promising future energy source. Although the ability of green algae to produce hydrogen has long been recognized (since 1939) and several biotechnological applications have been attempted, the greatest obstacle, being the O2-sensitivity of the hydrogenase enzyme, has not yet been overcome. In the present contribution, 75 years after the first report on algal hydrogen production, taking advantage of a natural mechanism of oxygen balance, we demonstrate high hydrogen yields by lichens. Lichens have been selected as the ideal organisms in nature for hydrogen production, since they consist of a mycobiont and a photobiont in symbiosis. It has been hypothesized that the mycobiont's and photobiont's consumption of oxygen (increase of COX and AOX proteins of mitochondrial respiratory pathways and PTOX protein of chrolorespiration) establishes the required anoxic conditions for the activation of the phycobiont's hydrogenase in a closed system. Our results clearly supported the above hypothesis, showing that lichens have the ability to activate appropriate bioenergetic pathways depending on the specific incubation conditions. Under light conditions, they successfully use the PSII-dependent and the PSII-independent pathways (decrease of D1 protein and parallel increase of PSaA protein) to transfer electrons to hydrogenase, while under dark conditions, lichens use the PFOR enzyme and the dark fermentative pathway to supply electrons to hydrogenase. These advantages of lichen symbiosis in combination with their ability to survive in extreme environments (while in a dry state) constitute them as unique and valuable hydrogen producing natural factories and pave the way for future biotechnological applications.

Proteomic strategy for the analysis of the polychlorobiphenyl-degrading cyanobacterium Anabaena PD-1 exposed to Aroclor 1254

The cyanobacterium Anabaena PD-1, which was originally isolated from polychlorobiphenyl (PCB)-contaminated paddy soils, has capabilities for dechlorinatin and for degrading the commercial PCB mixture Aroclor 1254. In this study, 25 upregulated proteins were identified using 2D electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). These proteins were involved in (i) PCB degradation (i.e., 3-chlorobenzoate-3,4-dioxygenase); (ii) transport processes [e.g., ATP-binding cassette (ABC) transporter substrate-binding protein, amino acid ABC transporter substrate-binding protein, peptide ABC transporter substrate-binding protein, putrescine-binding protein, periplasmic solute-binding protein, branched-chain amino acid uptake periplasmic solute-binding protein, periplasmic phosphate-binding protein, phosphonate ABC transporter substrate-binding protein, and xylose ABC transporter substrate-binding protein]; (iii) energetic metabolism (e.g., methanol/ethanol family pyrroloquinoline quinone (PQQ)-dependent dehydrogenase, malate-CoA ligase subunit beta, enolase, ATP synthase β subunit, FOF1 ATP synthase subunit beta, ATP synthase α subunit, and IMP cyclohydrolase); (iv) electron transport (cytochrome b6f complex Fe-S protein); (v) general stress response (e.g., molecular chaperone DnaK, elongation factor G, and translation elongation factor thermostable); (vi) carbon metabolism (methanol dehydrogenase and malate-CoA ligase subunit beta); and (vii) nitrogen reductase (nitrous oxide reductase). The results of real-time polymerase chain reaction showed that the genes encoding for dioxygenase, ABC transporters, transmembrane proteins, electron transporter, and energetic metabolism proteins were significantly upregulated during PCB degradation. These genes upregulated by 1.26- to 8.98-fold. These findings reveal the resistance and adaptation of cyanobacterium to the presence of PCBs, shedding light on the complexity of PCB catabolism by Anabaena PD-1.