Differential expression of peroxidase and ABC transporter as the key regulatory components for degradation of azo dyes by Penicillium oxalicum SAR-3

Physiological and transcriptome profiling of Chlorella sorokiniana: A study on azo dye wastewater decolorization

Over decades, synthetic dyes have become increasingly dominated by azo dyes posing a significant environmental risk due to their toxicity. Microalgae-based systems may offer an alternative for treatment of azo dye effluents to conventional physical-chemical methods. Here, microalgae were tested to decolorize industrial azo dye wastewater (ADW). Chlorella sorokiniana showed the highest decolorization efficiency in a preliminary screening test. Subsequently, the optimization of the experimental design resulted in 70% decolorization in a photobioreactor. Tolerance of this strain was evidenced using multiple approaches (growth and chlorophyll content assays, scanning electron microscopy (SEM), and antioxidant level measurements). Raman microspectroscopy was employed for the quantification of ADW-specific compounds accumulated by the microalgal biomass. Finally, RNA-seq revealed the transcriptome profile of C. sorokiniana exposed to ADW for 72 h. Activated DNA repair and primary metabolism provided sufficient energy for microalgal growth to overcome the adverse toxic conditions. Furthermore, several transporter genes, oxidoreductases-, and glycosyltransferases-encoding genes were upregulated to effectively sequestrate and detoxify the ADW. This work demonstrates the potential utilization of C. sorokiniana as a tolerant strain for industrial wastewater treatment, emphasizing the regulation of its molecular mechanisms to cope with unfavorable growth conditions.

Screening of Fungi Isolates for C-4 Hydroxylation of R-2-Phenoxypropionic Acid Based on a Novel 96-Well Microplate Assay Method

R-2-(4-Hydroxyphenoxy)propionic acid (R-HPPA) is a pivotal intermediate for the synthesis of aryloxyphenoxypropionate (APP) herbicide. To rapidly screen microbial isolates with the capacity of hydroxylating R-2-phenoxypropionic acid to R-HPPA from various environmental samples, a convenient and safe 96-well microplate assay method with sodium nitrite (NaNO₂) as chromogenic reagent was proposed and optimized. The optimum assay conditions were as follows: the detection wavelength was 420 nm, the concentration of NaNO₂ solution was 6.0 g/L, color reaction temperature was 60 °C, the pH of the NaNO₂ solution was 2.4, and the reaction time was 40 min. With the aid of this method, screening for microorganisms with C-4-specific hydroxylation activity of R-PPA was conducted. As a result, 23 strains among 3744 single colonies isolated from various samples exhibited the hydroxylation activity. Among these strains, the highest bioconversion rate was achieved by Penicillium oxalicum A5 and Aspergillus versicolor A12, respectively. After 72-h cultivation in shake flask, their conversion rates of R-HPPA from 10 g/L R-PPA reached 21.18% and 40.24%, respectively. The established method was effective in rapid screening of microbes capable of biosynthesizing R-HPPA through hydroxylation of R-PPA, and the obtained two fungi species could be potentially used for R-HPPA production.

Transcriptome and metabolome responses of Shewanella oneidensis MR-1 to methyl orange under microaerophilic and aerobic conditions

Shewanella oneidensis MR-1 degrades various azo dyes under microaerophilic and anaerobic conditions, but this process is inhibited under aerobic conditions. The mechanisms underlying azo dye biodegradation and inhibition remain unknown. Therefore, we investigated metabolic and transcriptional changes in strain MR-1, which was cultured under different conditions, to elucidate these mechanisms. At the transcriptional level, genes involved in certain metabolic processes, particularly the tricarboxylic acid (TCA) cycle, amino acid biodegradation, and the electron transfer system, were significantly altered (M ≧ 2, p > 0.8 ) in the presence of methyl orange (MO). Moreover, a high concentration of dissolved oxygen heavily impacted the expression levels of genes involved in fatty acid biodegradation. Metabolome analysis revealed significant alteration (p < 0.05) in the concentrations of nine metabolites when strain MR-1 was cultured under aerobic conditions; the majority of these metabolites were closely associated with amino acid metabolism and DNA replication. Accordingly, we propose a possible pathway for MO biodegradation and discuss the most likely causes of biodegradation inhibition due to dissolved oxygen.

Diverse Metabolic Capacities of Fungi for Bioremediation

Bioremediation refers to cost-effective and environment-friendly method for converting the toxic, recalcitrant pollutants into environmentally benign products through the action of various biological treatments. Fungi play a major role in bioremediation owing to their robust morphology and diverse metabolic capacity. The review focuses on different fungal groups from a variety of habitats with their role in bioremediation of different toxic and recalcitrant compounds; persistent organic pollutants, textile dyes, effluents from textile, bleached kraft pulp, leather tanning industries, petroleum, polyaromatic hydrocarbons, pharmaceuticals and personal care products, and pesticides. Bioremediation of toxic organics by fungi is the most sustainable and green route for cleanup of contaminated sites and we discuss the multiple modes employed by fungi for detoxification of different toxic and recalcitrant compounds including prominent fungal enzymes viz., catalases, laccases, peroxidases and cyrochrome P450 monooxygeneses. We have also discussed the recent advances in enzyme engineering and genomics and research being carried out to trace the less understood bioremediation pathways.