Abstract

The effective degradation of hazardous contaminants remains an intractable challenge in wastewater processing, especially for the high concentration of salty azo dye wastewater. However, some unique yeast symbionts identified from the termite gut system present an impressive function to deconstruct some aromatic compounds, which imply that they may be valued to work on the dye degradation for various textile effluents. In this investigation, a newly isolated and unique yeast strain, Sterigmatomyces halophilus SSA-1575, was identified from the gut system of a wood-feeding termite (WFT), Reticulitermes chinensis. Under the optimized ambient conditions, the yeast strain SSA-1575 showed a complete decolorization efficiency on Reactive Black 5 (RB5) within 24 h, where this azo dye solution had a concentration of a 50 mg/L RB5. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase (LiP) were determined as the key reductase and oxidase of S. halophilus SSA-1575. Enhanced decolorization was recorded when the medium was supplemented with carbon and energy sources, including glucose, ammonium sulfate, and yeast extract. To understand a possible degradation pathway well, UV-Vis spectroscopy, FTIR and Mass Spectrometry analyses were employed to analyze the possible decolorization pathway by SSA-1575. Determination of relatively high NADH-DCIP reductase suggested that the asymmetric cleavage of RB5 azo bond was mainly catalyzed by NADH-DCIP reductase, and finally resulting in the formation of colorless aromatic amines devoid of any chromophores. The ecotoxicology assessment of RB5 after a decolorization processing by SSA-1575, was finally conducted to evaluate the safety of its metabolic intermediates from RB5. The results of Microtox assay indicate a capability of S. halophilus SSA-1575, in the detoxification of the toxic RB5 pollutant. This study revealed the effectiveness of halotolerant yeasts in the eco-friendly remediation of hazardous pollutants and dye wastewater processing for the textile industry.

Highlights

  • The rapid development of industrialization is always associated with an increase in the complexity and waste toxicities, which are causing a cost, which is paid in terms of environmental pollution (Ali et al, 2018, 2020a,b)

  • Among xylanase-producing yeasts isolated from the gut symbionts of R. chinenesis (Ali et al, 2017), S. halophilus SSA1575 could efficiently decolorize various azo dyes (Table 1)

  • wood-feeding termite (WFT) and their gut symbionts have co-evolved into an efficient mini-bioreactor, including a suite of specialized enzymes that synergistically have a unique capability on the decomposition of lignin-derived compounds, making them the most abundant and sustainable solar batteries on earth (Sun et al, 2014)

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Summary

Introduction

The rapid development of industrialization is always associated with an increase in the complexity and waste toxicities, which are causing a cost, which is paid in terms of environmental pollution (Ali et al, 2018, 2020a,b). Many governments have established environmental laws and restrictions for aesthetic reasons and due to the serious ecological risks and toxicity on aquatic flora, as well as the mutagenicity and carcinogenicity of azo dye degradation products (Yang et al, 2018; Ali et al, 2019; Tkaczyk et al, 2020). Azo dyes, which represent one of the largest consuming dyestuff categories around the world, are major contributors that trigger severe environmental pollution issues due to their extensive use in textile and leather dyeing, paper printing, cosmetics and many other industries (Pattanaik et al, 2020; Tkaczyk et al, 2020). The disposal of azo dyes from their effluents, is of utmost importance before being discharged into an environment

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