Cr(VI) reduction by gluconolactone and hydrogen peroxide, the reaction products of fungal glucose oxidase: Cooperative interaction with organic acids in the biotransformation of Cr(VI)

Screening of Lactic Acid Bacteria Strains for Potential Sourdough and Bread Applications: Enzyme Expression and Exopolysaccharide Production

Twenty-eight strains of lactic acid bacteria (LAB) were characterized for the ability to express enzymes of interest (including protease, xylanase, α-amylase, laccase, and glucose oxidase) as well as the ability to produce exopolysaccharide (EPS). The screening of enzyme capability for all LAB strains proceeded in a progressive 3-stage manner that helps to profile the efficiency of LAB strains in expressing chosen enzymes (Stage 1), highlights the strains with affinity for flour as the substrate (Stage 2), and discerns strains that can adapt well in a simulated starter environment (Stage 3). The theoretical ability of LAB to express these enzymes was also assessed using Basic Local Alignment Search Tool (BLAST) analysis to identify the underlying genes in the whole genome sequence. By consolidating both experimental data and information obtained from BLAST, three LAB strains were deemed optimal in expressing enzymes, namely, Lb. delbrueckii subsp. bulgaricus (RBL 52), Lb. rhamnosus (RBL 102), and Lb. plantarum (ATCC 10241). Meanwhile, EPS-producing capabilities were observed for 10 out of 28 LAB strains, among which, Lactococcus lactis subsp. diacetylactis (RBL 37) had the highest total EPS yield (274.15 mg polysaccharide/L culture) and produced 46.2% polysaccharide with a molecular mass of more than 100 kDa.

The degradation of an aromatic organic compound by Aspergillus niger var tubingensis Ed8 produces metabolites that reduce Cr (VI)

Chromium Cr(VI) is a highly toxic environmental contaminant for any organism, its presence in the environment is mainly due to anthropogenic activities. The use of biotechnology has been implemented for the treatment of effluents contaminated with Cr(VI).Our working group has isolated several fungi and bacteria capable of removing Cr(VI) from the culture medium. Aspergillus niger var tubingensis Ed8 is a strain that can produce metabolites which reduce Cr (VI) to Cr (III). The objective of this work was to determine the effect of sodium salicylate on the growth of this strain and on the Cr(VI) reduction system, as well as to identify the metabolites that are produced from sodium salicylate. Our results show that the Culture medium containing sodium salicylate (20 mM) inhibits strain growth compared to the control condition (0 mM). However, it increases the specific reduction capacity of Cr (VI) red/mg Biomass in order of magnitude. Analysis of the culture medium corresponding to 48 h of incubation shows the presence of catechol and salicylate diminution. In addition, as a product of the enzymatic activity of a cell-free cellular extract, after 24 h of incubation, the consumption of salicylate is detected, as well as the presence of peaks corresponding to resorcinol and catechol. Our results show that it is possible to increase the Cr(VI) reducing capacity of the Ed8 strain, depending on the composition of the culture medium.

Mechanism of Cr(VI) reduction by Lysinibacillus sp. HST-98, a newly isolated Cr (VI)-reducing strain

Facing the increasingly severe Cr(VI) pollution, bioreduction has proved to be an eco-friendly remediation method. An isolated strain identified as Lysinibacillus can relatively reduce Cr(VI) well. Even if the concentration of Cr(VI) increased to 250mg/L, the strain HST-98 could also grow and remove Cr(VI) well. After optimization of reaction conditions, the optimal pH, temperature, and electron donor are 8~9, 36°C, and sodium lactate, respectively. Coexisting metal ions such as Cu2+, Co2+, and Mn2+ are beneficial to reduce Cr(VI), while Zn2+, Ni2+, and Cd2+ are just the opposite. What is more, the mechanism of the reduction by the strain HST-98 is chiefly mediated by intracellular enzymes. After gene sequence homology blast and analysis, the genes and enzymes related to chromium metabolism in strain HST-98 have been annotated, which helps us to further understand the reduction mechanism of the strain HST-98. In general, Lysinibacillus sp. HST-98 is a potential candidate to repair the Cr(VI)-contaminated sites.

Mycoremediation of heavy metals: processes, mechanisms, and affecting factors

Industrial processes and mining of coal and metal ores are generating a number of threats by polluting natural water bodies. Contamination of heavy metals (HMs) in water and soil is the most serious problem caused by industrial and mining processes and other anthropogenic activities. The available literature suggests that existing conventional technologies are costly and generated hazardous waste that necessitates disposal. So, there is a need for cheap and green approaches for the treatment of such contaminated wastewater. Bioremediation is considered a sustainable way where fungi seem to be good bioremediation agents to treat HM-polluted wastewater. Fungi have high adsorption and accumulation capacity of HMs and can be potentially utilized. The most important biomechanisms which are involved in HM tolerance and removal by fungi are bioaccumulation, bioadsorption, biosynthesis, biomineralisation, bioreduction, bio-oxidation, extracellular precipitation, intracellular precipitation, surface sorption, etc. which vary from species to species. However, the time, pH, temperature, concentration of HMs, the dose of fungal biomass, and shaking rate are the most influencing factors that affect the bioremediation of HMs and vary with characteristics of the fungi and nature of the HMs. In this review, we have discussed the application of fungi, involved tolerance and removal strategies in fungi, and factors affecting the removal of HMs.

Glucose oxidase modified Fenton reactions for in-situ ROS generation and potential application in groundwater remediation

Catalyzed H₂O₂ propagations (CHP) have demonstrated great potential in the remediation of chlorinated aliphatic hydrocarbons (CAHs) like trichloroethene (TCE) contaminated groundwater. However, the importation of highly unstable H₂O₂ into subsurface environment remains challenging. In this work, the in-situ H₂O₂ generation reaction between glucose oxidase (GOD) and glucose was applied in combination with Fe(II) to form the modified Fenton system (GMFs) and its performance in TCE oxidative degradation was investigated. The influence of reactant concentration as well as environmental factors like temperature and pH on the kinetics of TCE oxidation in GMFs were studied. At optimized conditions, about 78% TCE were removed within 8 h in GMFs, which remained effective over the temperature range of 15-30 °C and pH range of 3.6-6.0 (in acetate buffer). The in-situ H₂O₂ and OH generation capacity of GMFs were further investigated to elucidate their functional mechanism on TCE oxidation. Intermediate and product analysis indicated the near-complete release of chloride ion by TCE oxidation with few organic chlorinated intermediates detected. This work reveals the potential of GMFs for CAHs contaminated groundwater remediation through in-situ generation of reactive oxygen species.

Sonochemical reduction of Cr(VI) in air in the presence of organic additives: What are the involved mechanistic pathways?

The sonochemical (850 kHz) reduction of Cr(VI) (0.3 mM, pH 2, reactor open to air) was analyzed in the presence of different additives. The effects on Cr(VI) reduction efficiency of added formic acid (FA, 10 mM), citric acid (Cit, 2 mM), ethylenediaminetetraacetic acid (EDTA, 1 mM), methanol (MeOH, 0.1 M), ethanol (EtOH, 0.1 M), 2-propanol (2-PrOH, 0.1 M), tert-butanol (t-BuOH, 0.1 M), phenol (PhOH, 2 mM) and sodium lauryl sulfate (SLS, 1 mM) have been evaluated in comparison with the system in the absence of additives. Complete Cr(VI) reduction was obtained only when using EDTA (at 120 min) and Cit (at 180 min). Cr(III) complexes with these compounds or with their degradation products were detected as final products. For EDTA, Cit, t-BuOH, FA and SLS, the Cr(VI) decay could be adjusted to a zero-order kinetics; in the cases of MeOH, EtOH and 2-PrOH, there was a deviation from the zero-order kinetics. The Cr(VI) conversion increased in the order SLS (very low) < no additive ≅ MeOH ≅ EtOH ≅ 2-PrOH < FA < t-BuOH < PhOH < Cit < EDTA. The role of EDTA and Cit in stabilizing intermediate Cr(V) peroxo compounds and enhancing their direct transformation into different Cr(III) species is considered a major factor in the acceleration of Cr(VI) reduction processes. Mechanistic pathways are proposed.

Radiation induced environmental remediation of Cr(VI) heavy metal in aerated neutral solution under simulated industrial effluent

Cr(VI) compounds are major water contaminants in most industrial effluents, due to their carcinogenicity, while Cr(III) is an important element for human metabolism. In a previous work, we showed that Cr(VI) was radiolytically reduced to Cr(III) by the CO2ˉ• radical at pH 3 N2O-saturated solution in the presence of formate. Here in the present work, this removal was investigated by steady state irradiation and pulse radiolysis in aerated solution at neutral pH, which is close to natural conditions in most wastewaters, where the reducing agent is the superoxide radical anion O2ˉ•. The degradation of Cr(VI) increased linearly with the absorbed dose and was significantly enhanced by the added formate but not by the radiolitically produced hydrogen peroxide at this pH. The rate constant for this reduction was found to be 1.28×108 M−1 s−1 and the absorption spectrum of Cr(V) transient species was obtained. A partial recovery of Cr(VI) is observed over a period of ca. 5 ms following a second order kinetics with a rate constant 8.0×106 M−1 s−1. These outcomes suggest that gamma-irradiation of Cr(VI)-contaminated wastewaters and industrial effluents in presence of formate can be simple, effective and economical means for the remediation of this major contaminant.

Evaluation of chromate reductase activity in the cell-free culture filtrate of Arthrobacter sp. SUK 1201 isolated from chromite mine overburden

Arthrobacter sp. SUK 1201, a chromate resistant and reducing bacterium isolated from chromite mine overburden of Sukinda valley, Odisha, India has been evaluated for its hexavalent chromium [Cr(VI)] reduction potential using cell-free culture filtrate as extracellular chromate reductase enzyme. Production of the enzyme was enhanced in presence of Cr(VI) and its reducing efficiency was increased with increasing concentration of Cr(VI). The Michaelis-Menten constant (Km) and the maximum specific velocity (Vmax) of the extracellular Cr(VI) reductase were calculated to be 54.03 μM Cr(VI) and 5.803 U mg(-1) of protein respectively showing high affinity towards Cr(VI). The reducing activity of the enzyme was maximum at pH 6.5-7.5 and at a temperature of 35 °C and was dependent on NADH. The enzyme was tolerant to different metals such as Mn(II), Mg(II) and Fe(III) and was able to reduce Cr(VI) present in chromite mine seepage. These findings suggest that the extracellular chromate reductase of Arthrobacter sp. SUK 1201 has a great promise for use in Cr(VI) detoxification under different environmental conditions, particularly in the mining waste water treatment systems.