Enzymatic biodegradation, kinetic study, and detoxification of Reactive Red-195 by Halomonas meridiana isolated from Marine Sediments of Andaman Sea, India

Biodegradation and detoxification study of triphenylmethane dye (Brilliant green) in a recirculating packed-bed bioreactor by bacterial consortium

In the last few decades, Brilliant green (BG) dye is widely employed to colour the fabric materials in various industries (e.g. textile, pulp and paper, etc.). The wastewater containing BG dye emerges as a major challenge among the researchers due to its toxic, mutagenic, and carcinogenic effects on human beings and marine life. In this context, the present study is mainly focused on the biodegradation of BG dye present in wastewater. The biodegradation of BG dye was performed in an indigenously designed recirculating packed bed bioreactor (RPBBR). Modified Polypropylene-Polyurethane foam (PP-PUF), a support packing material, was immobilised with a newly isolated bacterial consortium of Enterobacter asburiae strain SG43 (BGT1) and Alcaligenes sp. SY1 (BGT2). The bioreactor was operated under various organic loading rates (OLRs) of 2.7, 1.27, 0.93, 0.71, and 0.53 kg COD/m3.d-1 with a hydraulic retention time (HRT) of 4 days. The bioreactor exhibited the maximum BG dye removal efficiency of 91%. Proton Nuclear Magnetic Resonance (1H NMR), UV-Vis spectroscopy, Gas chromatography-mass spectrometry (GC-MS), and Fourier Transform Infrared Spectroscopy (FTIR) depicted the biodegradation of BG dye. Phaseolus mungo seeds germinated in BG dye biodegraded wastewater was significantly high (83.56%) than the untreated wastewater (32.4%), which was reasonably subjected to the detoxification of treated wastewater.

Bioremediation of reactive orange 16 by industrial effluent-adapted bacterial consortium VITPBC6: process optimization using response surface methodology (RSM), enzyme kinetics, pathway elucidation, and detoxification

Textile effluent is one of the most hazardous industrial pollutant sources. It is generated in huge volumes and contains a wide array of toxicants. Reactive azo dyes, which are xenobiotic compounds, are predominantly utilized by textile industries for dyeing cotton, viscose, wool, and silk. The conventional physicochemical treatments used by industrial effluent treatment plants are ineffective in dye degradation. The present study thus attempted to find a potential treatment for reactive azo dyes. A novel bacterial consortium VITPBC6 was constructed with the most potent and compatible reactive orange 16 (RO-16) decolorizing isolates of tannery and textile effluents, and the isolates were identified as Bacillus flexus VITSP6, Bacillus paraflexus VITSPB7, Bacillus megaterium VITSPB9, Bacillus firmus VITEPB1, B. flexus VITEPB2, and Bacillus aryabhattai VITEPB3. The physicochemical factors of RO-16 decolorization were optimized by response surface methodology. Consortium VITPBC6 was able to tolerate a high concentration of RO-16 up to 800 mg L^-1. A cocktail of enzymes including azoreductase, tyrosinase, laccase, lignin peroxidase, and manganese peroxidase was involved in RO-16 degradation by VITPBC6. Consortium VITPBC6 degraded RO-16 following zero-order reaction. The enzymes of consortium VITPBC6 had a V_max of 352 mg L^-1 day^-1 for RO-16 degradation; however, the K_m value was high. VITPBC6 biodegraded RO-16 resulting in the formation of small aromatic compounds. Lastly, different toxicity assays conducted with untreated RO-16 and its corresponding biodegraded metabolite revealed that the toxicity of biodegraded metabolites was significantly lower than the untreated dye.

A novel promising laccase from the psychrotolerant and halotolerant Antarctic marine Halomonas sp. M68 strain

Microbial communities inhabiting the Antarctic Ocean show psychrophilic and halophilic adaptations conferring interesting properties to the enzymes they produce, which could be exploited in biotechnology and bioremediation processes. Use of cold- and salt-tolerant enzymes allows to limit costs, reduce contaminations, and minimize pretreatment steps. Here, we report on the screening of 186 morphologically diverse microorganisms isolated from marine biofilms and water samples collected in Terra Nova Bay (Ross Sea, Antarctica) for the identification of new laccase activities. After primary screening, 13.4 and 10.8% of the isolates were identified for the ability to oxidize 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the dye azure B, respectively. Amongst them, the marine Halomonas sp. strain M68 showed the highest activity. Production of its laccase-like activity increased six-fold when copper was added to culture medium. Enzymatic activity-guided separation coupled with mass spectrometry identified this intracellular laccase-like protein (named Ant laccase) as belonging to the copper resistance system multicopper oxidase family. Ant laccase oxidized ABTS and 2,6-dimethoxy phenol, working better at acidic pHs The enzyme showed a good thermostability, with optimal temperature in the 40-50°C range and maintaining more than 40% of its maximal activity even at 10°C. Furthermore, Ant laccase was salt- and organic solvent-tolerant, paving the way for its use in harsh conditions. To our knowledge, this is the first report concerning the characterization of a thermo- and halo-tolerant laccase isolated from a marine Antarctic bacterium.

Biological Mineralization of Methyl Orange by Pseudomonas aeruginosa

Due to its recalcitrant and carcinogenic nature, the presence of methyl orange (MO) in the environment is a serious threat to human and animal life and is also toxic to plants. MO being recalcitrant cannot be effectively reclaimed from industrial effluents through physical and chemical approaches. Biological methods on the other hand have the potential to degrade such dyes because of their compatibility with nature and low chances of adverse effects on the environment. Bacteria, due to their fast growth rate and capability of surviving in extreme environments can effectively be used for this purpose. In the current research study, Pseudomonas aeruginosa was isolated and characterized using 16rRNA from textile wastewater. In the preliminary tests it was found that Pseudomonas aeruginosa has the ability to degrade and mineralize methyl orange effectively. The physicochemical conditions were then optimized, in order to get maximum degradation of MO which was achieved at 37 °C, a pH of 7, a low salt concentration of 0.1 g/15 mL, a high carbon source of 0.6 g/15 mL, and 72 h experimental time. In a single set of experiments where all these optimum conditions were combined, 88.23% decolorization of the selected dye was achieved. At the end of the experimental cycle, the aliquots were homogenized and filtered. The filtrates were subjected to FTIR and GC-MS analysis where azo linkage breaking was confirmed from the FTIR spectra. The filtrates were then extracted with ethyl acetate and then passed through a silica gel column. On the basis of Rf value (TLC plates used) similar fraction were combined which were then subjected to NMR analysis. The compounds detected through GC-MS, peaks were not observed in proton and C-13 NMR. Instead, solvent and some impurity peaks were present, showing that complete mineralization of the dye had occurred due to the action of different bacterial enzymes such as azoreductase, peroxidases, and classes on MO. The prosed mechanism of complete mineralization is based on spectral data that needs to be verified by trapping the individual step products through the use of appropriate inhibitors of individual enzymes.