Degradation of Bisphenol-A: A Contaminant of Emerging Concern Using Catalytic Ozonation By Activated Carbon Impregnated Nanocomposite-Bimetallic Catalyst

Rampant water pollution events and rising water demand caused by exponential population growth and depleting freshwater resources speak of an impending water crisis. The inability of conventional wastewater treatment systems to remove Contaminants of Emerging Concern (CEC) such as Bisphenol-A (BPA) beckons for new and efficient technologies to remove them from wastewater and water sources. Advanced oxidation processes such as ozonation are primarily known for their capability to oxidize and degrade organic entities in water but optimum mineralization levels were hard to achieve. In this study, we synthesized an activated carbon impregnated nanocomposite-bimetallic catalyst (AC/CeO2/ZnO) and used it along with ozonation to remove BPA from water. The catalyst was characterized using BET, XRD, FESEM, Raman spectra, and DLS studies. Catalytic ozonation achieved TOC removal 25% higher than non-catalytic ozonation process. The degradation pathway of BPA was proposed using LC-MS/LC-Q-TOF studies that found six main aromatic degradation byproducts. Catalytic ozonation and non-catalytic ozonation followed similar degradation pathways. The formation of persistent aliphatic acidic byproducts in the treated sample made TOC removal above 61% difficult.

Managing Gene Expression in Pseudomonas Simiae EGD-AQ6 for Chloroaromatic Compound Degradation

Pseudomonas simiae EGD-AQ6 showed utilization of chloroaromatic compound, 2-4-dichlorophenoxyacetic acid (2,4-D) efficiently in its biofilm phenotype. The differential rates of accumulation of intermediate metabolite 4-chlorocatechol (4-CCA) were significant in both planktonic and biofilm phenotypes; also increased number of biofilm cells were observed during 2,4-D utilization. Interestingly, response surface analysis demonstrated the combined positive effects of 2,4-D degradation and 4-CCA accumulations. Also, gene expression profiles showed significant up-regulation of degradative and biofilm genes (particularly pellicle forming genes) in the biofilm phenotypes than their planktonic counterparts, thereby confirming occurrence of phenotype variations of Pseudomonas simiae EGD-AQ6 during chloroaromatic degradation. Furthermore, the sequence similarity of the 2-4-D catabolic genes and biofilm forming proteins (pel ABCDEFG and pga ABCD) which are responsible for building carbohydrate rich extracellular matrix, were significant with the respective organisms as revealed through genome analysis. This is the first report, which endorses this Pseudomonas simiae species to be unique in chloro-aromatic degradation through phenotype variation, thereby proving as a potential candidate in the improvement of bioremediation technologies.

Anthropogenic Activities Destabilized Bacterial Co-occurrence Networks in a Subtropical River

Previous studies suggested that strong positive correlations between microbial taxa destabilized microbial co-occurrence network, because network members which had strong positive correlations with each other tended to decrease in abundance synchronously. Anthropogenic activities have strong influences on microbial community composition and diversity in riverine ecosystems, but how they influence the stability of microbial co-occurrence network remain unclear. In this study, we used nutrient concentrations (nitrogen and phosphorus) as an indicator for anthropogenic activities, and explored the effects of anthropogenic activities on the stability of bacterial co-occurrence networks in a subtropical river, Xiyuan River. The nutrient concentrations were higher in midstream and downstream areas than in upstream area of Xiyuan River. The average proportion and correlation coefficient of positive correlations were higher in midstream and downstream networks than in upstream networks, indicating frequent anthropogenic activities destabilized the bacterial co-occurrence networks. To further explore the mechanisms, we found that the changes of network stabilities were associated with the changes of bacterial functions. Anthropogenic activity tolerant bacteria (e.g. nutrient removal, aromatic degradation and pathogen bacteria) and their linked bacterial members formed the large and strong positive modules in the midstream and downstream networks, and thus destabilized the networks. Based on network perspective, our results provide a new insight in the mechanisms of how anthropogenic activities alter riverine microbial communities.

Redundancy in Aromatic O-Demethylation and Ring-Opening Reactions in Novosphingobium aromaticivorans and Their Impact in the Metabolism of Plant-Derived Phenolics

ABSTRACT Lignin is a plant heteropolymer composed of phenolic subunits. Because of its heterogeneity and recalcitrance, the development of efficient methods for its valorization still remains an open challenge. One approach to utilize lignin is its chemical deconstruction into mixtures of monomeric phenolic compounds, followed by biological funneling into a single product. Novosphingobium aromaticivorans DSM 12444 has been previously engineered to produce 2-pyrone-4,6-dicarboxylic acid (PDC) from depolymerized lignin by simultaneously metabolizing multiple aromatics through convergent routes involving the intermediates 3-methoxygallic acid (3-MGA) and protocatechuic acid (PCA). We investigated enzymes predicted to be responsible for O-demethylation and oxidative aromatic ring opening, two critical reactions involved in the metabolism of phenolic compounds by N. aromaticivorans. The results showed the involvement of DesA in O-demethylation of syringic and vanillic acids, LigM in O-demethylation of vanillic acid and 3-MGA, and a new O-demethylase, DmtS, in the conversion of 3-MGA into gallic acid (GA). In addition, we found that LigAB was the main aromatic ring-opening dioxygenase involved in 3-MGA, PCA, and GA metabolism and that a previously uncharacterized dioxygenase, LigAB2, had high activity with GA. Our results indicate a metabolic route not previously identified in N. aromaticivorans that involves O-demethylation of 3-MGA to GA. We predict that this pathway channels ∼15% of the carbon flow from syringic acid, with the rest following ring opening of 3-MGA. The new knowledge obtained in this study allowed for the creation of an improved engineered strain for the funneling of aromatic compounds that exhibits stoichiometric conversion of syringic acid into PDC. IMPORTANCE For lignocellulosic biorefineries to effectively contribute to reduction of fossil fuel use, they need to become efficient at producing chemicals from all major components of plant biomass. Making products from lignin will require engineering microorganisms to funnel multiple phenolic compounds to the chemicals of interest, and N. aromaticivorans is a promising chassis for this technology. The ability of N. aromaticivorans to efficiently and simultaneously degrade many phenolic compounds may be linked to having functionally redundant aromatic degradation pathways and enzymes with broad substrate specificity. A detailed knowledge of aromatic degradation pathways is thus essential to identify genetic engineering targets to maximize product yields. Furthermore, knowledge of enzyme substrate specificity is critical to redirect flow of carbon to desired pathways. This study described an uncharacterized pathway in N. aromaticivorans and the enzymes that participate in this pathway, allowing the engineering of an improved strain for production of PDC from lignin.

Functional pathway redundancy in the metabolism of plant-derived phenolics by Novosphingobium aromaticivorans

ABSTRACTLignin is a plant heteropolymer composed of phenolic subunits. Because of its heterogeneity and recalcitrance, the development of efficient methods for its valorization still remains an open challenge. One approach to utilize lignin is its chemical deconstruction into mixtures of monomeric phenolic compounds followed by biological funneling into a single product. Novosphingobium aromaticivorans DSM12444 has been previously engineered to produce 2-pyrone-4,6-dicarboxylic acid (PDC) from depolymerized lignin by simultaneously metabolizing multiple aromatics through convergent routes involving the intermediates 3-methoxygallic acid (3-MGA) and protocatechuic acid (PCA). We investigated enzymes predicted to be responsible for O-demethylation and oxidative aromatic ring opening, two critical reactions involved in the metabolism of phenolics compounds by N. aromaticivorans. The results showed the involvement of DesA in O-demethylation of syringic and vanillic acids, LigM in O-demethylation of vanillic acid and 3-MGA, and a new O-demethylase, DmtS, in the conversion of 3-MGA into gallic acid (GA). In addition, we found that LigAB was the main aromatic ring opening dioxygenase involved in 3-MGA, PCA, and GA metabolism, and that a previously uncharacterized dioxygenase, LigAB2, had high activity with GA. Our results indicate a metabolic route not previously identified in N. aromaticivorans that involves O-demethylation of 3-MGA to GA. We predict this pathway channels ∼15% of the carbon flow from syringic acid, with the rest following ring opening of 3-MGA. The new knowledge obtained in this study allowed for the creation of an improved engineered strain for the funneling of aromatic compounds that exhibits stoichiometric conversion of syringic acid into PDC.IMPORTANCEFor lignocellulosic biorefineries to effectively contribute to reduction of fossil fuel use, they need to become efficient at producing chemicals from all major components of plant biomass. Making products from lignin will require engineering microorganisms to funnel multiple phenolic compounds to the chemicals of interest, and N. aromaticivorans is a promising chassis for this technology. The ability of N. aromaticivorans to efficiently and simultaneously degrade many phenolic compounds may be linked to having functionally redundant aromatic degradation pathways and enzymes with broad substrate specificity. A detailed knowledge of aromatic degradation pathways is thus essential to identify genetic engineering targets to maximize product yields. Furthermore, knowledge of enzyme substrate specificity is critical to redirect flow of carbon to desired pathways. This study described an uncharacterized pathway in N. aromaticivorans and the enzymes that participate in this pathway, allowing the engineering of an improved strain for production of PDC from lignin.