Statistical modeling and optimization of Toluidine Red biodegradation in a synthetic wastewater using strain Gb

Potential of halophiles and alkaliphiles in bioremediation of azo dyes-laden textile wastewater: a review

Azo dye-laden textile wastewater must be treated before release due to various health and environmental concerns. Bioremediation of textile wastewater, however, is a challenge owing to its alkaline and saline nature as mesophilic microbes, in general, are either not able to thrive or show less efficiency under such hostile environment. Thus, pre-treatment for neutralization or salinity removal becomes a prerequisite before applying microbes for treatment, causing extra economical and technical burden. Extremophilic bacteria can be the promising bioremediating tool because of their inherent ability to survive and show toxicants removal capability under such extreme conditions without need of pre-treatment. Among extremophiles, halophilic and alkaliphilic bacteria which are naturally adapted to high salt and pH are of special interest for the decolorization of saline-alkaline-rich textile wastewater. The current review article is an attempt to provide an overview of the bioremediation of azo dyes and azo dye-laden textile wastewater using these two classes of extremophilic bacteria. The harmful effects of azo dyes on human health and environment have been discussed herein. Halo-alkaliphilic bacteria circumvent the extreme conditions by various adaptations, e.g., production of certain enzymes, adjustment at the protein level, pH homeostasis, and other structural adaptations that have been highlighted in this review. The unique properties of alkaliphiles and halophiles, to not only sustain but also harboring high dye removal competence at high pH and salt concentration, make them a good candidate for designing future bioremediation strategies for the management of alkaline, salt, and azo dye-laden industrial wastewaters.

Ecotoxic side-effects of allelochemicals on submerged plant and its associated microfloras effectively relieved by sustained-release microspheres

Harmful algae bloom caused by water eutrophication is a burning question worldwide. Allelochemicals sustained-release microspheres (ACs-SMs) exhibited remarkable inhibition effect on algae, however, few studies have focused on the ecotoxic side-effects of ACs-SMs on submerged plant and its associated microfloras. Herein the effects of different exposure situations including single high-concentration ACs (15 mg/L, SH-ACs), repeated low-concentration ACs (3 × 5 mg/L, RL-ACs) and ACs-SMs containing 15 mg/L ACs on morphological indexes, chlorophyll content, lipid peroxidation, enzymatic activity, and chlorophyll fluorescence indexes of submerged plant Vallisneria natans and the richness and diversity of its associated microfloras (epibiotic microbes and sediment microbes) were studied. The results showed that pure ACs (RL-ACs and SH-ACs groups) had negative effects on plant height, mean leaf number and area of V. natans, but promoted the increase of mean leaf length. In addition, pure ACs caused lipid peroxidation, activated the antioxidant defense system, decreased chlorophyll content, and damaged photosynthetic system in leaves. Interestingly, ACs-SMs not only had barely negative effects on above indexes of V. natans, but had certain positive effects at the later experiment stage (days 50-60). Pure ACs and ACs-SMs all reduced the richness and diversity of microfloras in each group, and promoted the increase of relative abundance of dominant bacteria Pseudomonas, leading to a simpler community structure. Significantly, V. natans leaves diminished the effects of pure ACs and ACs-SMs on epibiotic microbes, and the plant rhizosphere was beneficial to the increase of dominant bacteria that promoted plant growth. Thus, sustained-release microspherification technology can effectively relieve the ecotoxic side-effects of pure ACs on submerged plant and its associated microfloras. This study fills the gap on the ecological safety knowledge of ACs-SMs and provides primary data for evaluating the feasibility and commercialization prospects of ACs-SMs as algae inhibitor in aquatic ecosystem.

Decolorization mechanism, identification of an FMN-dependent NADH-azoreductase from a moderately halotolerant Staphylococcus sp. MEH038S, and toxicity assessment of biotransformed metabolites

The application of halotolerant microorganisms capable of decolorizing is attractive. Decolorization mechanism, the effect of different parameters on the decolorization percentage, and toxicity analysis of Reactive Black 5 before and after decolorization were investigated in the present study. The decolorization percentage for live cells of Staphylococcus sp. strain MEH038S was more than dead cells, which demonstrated that Reactive Black 5 was decolorized through the degradation process. The results confirmed that an FMN-dependent NADH-azoreductase gene was responsible for the decolorization and then was identified as Staphylococcus sp. EFS01 azoreductase from a moderately halotolerant Staphylococcus strain for the first time. The maximal decolorization of 98.15% was observed at pH 6.5 and 35 ^° C for 50 mg/L of Reactive Black 5. In addition, more than 90% decolorization was achieved with 5-40 g/L of NaCl. The results of Gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy showed that Reactive Black 5 was broken to the lower molecular weight compounds without any chromophoric azo groups. Phytotoxicity and fish toxicity proved that the biotransformed metabolites of Reactive Black 5 degradation were more toxic than the original dye. The moderate halotolerant strain exhibited a remarkable decolorization capability and can be applied for textile wastewater treatment. PRACTITIONER POINTS: An azoreductase gene from a moderately halotolerant Staphylococcus was identified. More than 90% decolorization efficiency was observed under high-salt conditions. Biotransformed metabolites of RB5 degradation were identified. Toxicity analysis of biotransformed metabolites was investigated.

Study on the osmoregulation of "Halomonas socia" NY-011 and the degradation of organic pollutants in the saline environment

"Halomonas socia" NY-011, a new species of moderately halophilic bacteria isolated and identified in our laboratory, can grow in high concentrations of salt ranging from 0.5 to 25%. In this study, the whole genome of NY-011 was sequenced and a detailed analysis of the genomic features was provided. Especially, a series of genes related to salt tolerance and involved in xenobiotics biodegradation were annotated by COG, GO and KEGG analyses. Subsequently, RNA-Seq-based transcriptome analysis was applied to explore the osmotic regulation of NY-011 subjected to high salt stress for different times (0 h, 1 h, 3 h, 6 h, 11 h, 15 h). And we found that the genes related to osmoregulation including excluding Na⁺ and accumulating K⁺ as well as the synthesis of compatible solutes (alanine, glutamate, ectoine, hydroxyectoine and glycine betaine) were up-regulated, while the genes involved in the degradation of organic compounds were basically down-regulated during the whole process. Specifically, the expression trend of genes related to osmoregulation increased firstly then dropped, which was almost opposite to that of degrading organic pollutants genes. With the prolongation of osmotic up-shock, NY-011 survived and gradually adapted to osmotic stress, the above-mentioned two classes of genes slowly returned to normal expression level. Then, the scanning electron microscope (SEM) and transmission electron microscope (TEM) were also utilized to observe morphological properties of NY-011 under hypersaline stress, and our findings showed that the cell length of NY-011 became longer under osmotic stress, at the same time, polyhydroxyalkanoates (PHAs) were synthesized in the cells. Besides, physiological experiments confirmed that NY-011 could degrade organic compounds in a high salt environment. These data not only provide valuable insights into the mechanism of osmotic regulation of NY-011; but also make it possible for NY-011 to be exploited for biotechnological applications such as degrading organic pollutants in a hypersaline environment.