Genotoxicity evaluation of tannery effluent treated with newly isolated hexavalent chromium reducing Bacillus cereus

Harnessing native bacterial consortium to boost duckweed biomass and chromium removal from batik industry effluents

Batik industry is one of the largest contributors to chromium hexavalent (Cr(VI)) pollution due to the dying and pigmenting process. Remediation agents such as duckweed and bacteria have been commonly used to treat wastewater (WW)-containing Cr(VI). This study utilized native bacterial consortium from the batik WW environment to enhance duckweed growth and Cr(VI) removal. Among the formulated consortia, consortium G4 showed the highest growth promotion on duckweed in WW by 1.3 to 2-fold, while other consortia showed a contrasting result. Additionally, duckweed chromium uptake in WW reached 74 % after 12 days when applied with G4. Consortium G4 features two plant growth-promoting bacteria, Enterobacter mori TALD 1.2 and Enterobacter cloacae TALA 5, along with two chromium-reducing bacteria, Lysinibacillus fusiformis TALA 1.1 and Bacillus thuringiensis TA1. Several combinations of the G4 members were also tested for chromium reduction activity in an NB medium containing 100 mg L-1 Cr(VI). The original G4 combination showed the fastest Cr(VI) removal, achieving an 81.93 % Cr(VI) reduction within 48 h and a 99 % reduction within 105 h. Interestingly, combining only the chromium-reducing bacteria TALA 1.1 and TA 1 significantly reduced chromium reduction activity and bacterial growth, possibly due to carbon source competition. Thus, the complete members of consortium G4 enhance cross-feeding, with each species playing a vital role in improving interspecies interactions and aiding in chromium reduction. This study underscores the importance of designing a specific and compatible consortium to collaborate with duckweed, offering insights into environmental management practices for other contaminated sites.

Unveiling the chromate stress response in the marine bacterium Bacillus enclensis AGM_Cr8: a multifaceted investigation

In this study, we introduce Bacillus enclensis AGM_Cr8, a gram-positive marine bacterium isolated from the chronically polluted Versova Creek in Mumbai, India. AGM_Cr8 exhibits robust tolerance to chromate stress, thriving in marine agar media containing up to 3200 mg/l of hexavalent chromium [Cr(VI)], with the Minimum Inhibitory Concentration (MIC) established at 5000 mg/l. Notably, AGM_Cr8 also displays tolerance to other heavy metals, including Lead [Pb (II)] (1200 mg/l), Arsenic [As (III)] (400 mg/l), Cadmium [Cd(II)] (100 mg/l), and Nickel [Ni(II)] (100 mg/l). Scanning Electron Microscopy (SEM) reveals the presence of Cr(VI) on the bacterial surface, accompanied by the secretion of extracellular polymeric substances (EPSs) facilitating Cr(VI) sequestration. This observation is validated through Energy Dispersive Spectroscopy (EDS). Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy (STEM-EDS) confirm internal bioaccumulation of Cr(VI). X-ray photoelectron spectroscopy (XPS) identifies distinct peaks around 579 and 576 eV, indicating the coexistence of Cr(VI) and Cr(III), implying a bioreduction mechanism. De novo genome sequencing identifies twenty-two chromate-responsive genes, including putative chromate transporters (srpC1 and srpC2), suggesting an efflux mechanism. Other identified genes encode NAD(P)H-dependent FMN-containing oxidoreductase, NADH quinone reductase, ornithine aminotransferase, transporter genes (natA, natB, ytrB), and genes related to DNA replication and repair (recF), DNA mismatch repair (mutH), and superoxide dismutase. We therefore, propose a chromate detoxification pathway that involves an interplay of chromate transporters, enzymatic reduction of Cr(VI) to Cr(III), DNA repair and role of antioxidants in response to chromate stress. We have highlighted the potential of AGM_Cr8 for bioremediation in chromium-contaminated environments, given its robust tolerance and elucidated molecular mechanisms for detoxification.

Bacterial biofilm-mediated environmental remediation: Navigating strategies to attain Sustainable Development Goals

Bacterial biofilm is a structured bacterial community enclosed within a three-dimensional polymeric matrix, governed by complex signaling pathways, including two-component systems, quorum sensing, and c-di-GMP, which regulate its development and resistance in challenging environments. The genetic configurations within biofilm empower bacteria to exhibit significant pollutant remediation abilities, offering a promising strategy to tackle diverse ecological challenges and expedite progress toward Sustainable Development Goals (SDGs). Biofilm-based technologies offer advantages such as high treatment efficiency, cost-effectiveness, and sustainability compared to conventional methods. They significantly contribute to agricultural improvement, soil fertility, nutrient cycling, and carbon sequestration, thereby supporting SDG 1 (No poverty), SDG 2 (Zero hunger), SDG 13 (Climate action), and SDG 15 (Life on land). In addition, biofilm facilitates the degradation of organic-inorganic pollutants from contaminated environments, aligning with SDG 6 (Clean water and sanitation) and SDG 14 (Life below water). Bacterial biofilm also has potential applications in industrial innovation, aligning SDG 7 (Affordable and clean energy), SDG 8 (Decent work and economic growth), and SDG 9 (Industry, innovation, and infrastructure). Besides, bacterial biofilm prevents several diseases, aligning with SDG 3 (Good health and well-being). Thus, bacterial biofilm-mediated remediation provides advanced opportunities for addressing environmental issues and progressing toward achieving the SDGs. This review explores the potential of bacterial biofilms in addressing soil pollution, wastewater, air quality improvement, and biodiversity conservation, emphasizing their critical role in promoting sustainable development.

Plant growth-promoting rhizobacterial secondary metabolites in augmenting heavy metal(loid) phytoremediation: An integrated green in situ ecorestorative technology

In recent times, increased geogenic and human-centric activities have caused significant heavy metal(loid) (HM) contamination of soil, adversely impacting environmental, plant, and human health. Phytoremediation is an evolving, cost-effective, environment-friendly, in situ technology that employs indigenous/exotic plant species as natural purifiers to remove toxic HM(s) from deteriorated ambient soil. Interestingly, the plant's rhizomicrobiome is pivotal in promoting overall plant nutrition, health, and phytoremediation. Certain secondary metabolites produced by plant growth-promoting rhizobacteria (PGPR) directly participate in HM bioremediation through chelation/mobilization/sequestration/bioadsorption/bioaccumulation, thus altering metal(loid) bioavailability for their uptake, accumulation, and translocation by plants. Moreover, the metallotolerance of the PGPR and the host plant is another critical factor for the successful phytoremediation of metal(loid)-polluted soil. Among the phytotechniques available for HM remediation, phytoextraction/phytoaccumulation (HM mobilization, uptake, and accumulation within the different plant tissues) and phytosequestration/phytostabilization (HM immobilization within the soil) have gained momentum in recent years. Natural metal(loid)-hyperaccumulating plants have the potential to assimilate increased levels of metal(loid)s, and several such species have already been identified as potential candidates for HM phytoremediation. Furthermore, the development of transgenic rhizobacterial and/or plant strains with enhanced environmental adaptability and metal(loid) uptake ability using genetic engineering might open new avenues in PGPR-assisted phytoremediation technologies. With the use of the Geographic Information System (GIS) for identifying metal(loid)-impacted lands and an appropriate combination of normal/transgenic (hyper)accumulator plant(s) and rhizobacterial inoculant(s), it is possible to develop efficient integrated phytobial remediation strategies in boosting the clean-up process over vast regions of HM-contaminated sites and eventually restore ecosystem health.

Reduction of hexavalent chromium using Bacillus safensis isolated from an abandoned mine

The present work focused on the isolation of a bacterial strain multi-resistant to heavy metals with a high potential for reducing hexavalent chromium (Cr(VI)) and studied its Cr(VI) removal performance in immobilized state and the mechanisms involved. Bacterial isolate was identified as Bacillus safensis CCMM B629 (B. safensis), is able to completely reduce 50, 100 and 200 mg/L of Cr(VI) after 24, 48 and 120 h, respectively under optimized conditions of pH 7 and 30°C. The coexistence of nitrates, cadmium and mercury inhibits reduction, while copper and iron significantly improve removal efficiencies. Additionally, the presence of electron donors such as glycerol, glucose and citrate significantly increases bioreduction rate. Cells immobilized in alginate beads successfully reduced Cr(VI) compared to free cells, showing the performance of biobeads in Cr(VI) reduction. Membrane fraction exhibited highest rate of Cr(VI) reduction (65%) compared to other cellular components, indicating that Cr(VI) reduction occurred primarily in cell membrane. Further characterization of Cr(VI) removal by B. safensis cells using scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis showed its ability to reduce and adsorb Cr(VI), confirming that hexavalent chromium was taken up successfully on bacterial cell surfaces. Based on Fourier transform infrared spectroscopy analysis (FTIR), hydroxyl, carboxyl, amide, and phosphoryl functional groups participated in combination with Cr(III). In conclusion, B. safensis is a bacterium with great potential for Cr(VI) removal, and it is a promising and competitive strain for use in bioremediation of Cr(VI) contaminated industrial effluents.

Bioremediation of petroleum refinery wastewater using Bacillus subtilis IH-1 and assessment of its toxicity

Environmental contamination from petroleum refinery operations has increased due to the rapid population growth and modernization of society, necessitating urgent repair. Microbial remediation of petroleum wastewater by prominent bacterial cultures holds promise in circumventing the issue of petroleum-related pollution. Herein, the bacterial culture was isolated from petroleum-contaminated sludge samples for the valorization of polyaromatic hydrocarbons and biodegradation of petroleum wastewater samples. The bacterial strain was screened and identified as Bacillus subtilis IH-1. After six days of incubation, the bacteria had degraded 25.9% of phenanthrene and 20.3% of naphthalene. The treatment of wastewater samples was assessed using physico-chemical and Fourier-transform infrared spectroscopy analysis, which revealed that the level of pollutants was elevated and above the allowed limits. Following bacterial degradation, the reduction in pollution parameters viz. EC (82.7%), BOD (87.0%), COD (80.0%), total phenols (96.3%), oil and grease (79.7%), TKN (68.8%), TOC (96.3%) and TPH (52.4%) were observed. The reduction in pH and heavy metals were also observed after bacterial treatment. V. mungo was used in the phytotoxicity test, which revealed at 50% wastewater concentration the reduction in biomass (30.3%), root length (87.7%), shoot length (93.9%), and seed germination (30.0%) was observed in comparison to control. When A. cepa root tips immersed in varying concentrations of wastewater samples, the mitotic index significantly decreased, suggesting the induction of cytotoxicity. However, following the bacterial treatment, there was a noticeable decrease in phytotoxicity and cytotoxicity. The bacterial culture produces lignin peroxidase enzyme and has the potential to degrade the toxic pollutants of petroleum wastewater. Therefore the bacterium may be immobilised or directly used at reactor scale or pilot scale study to benefit the industry and environmental safety.

Treatment of low-pH rubber wastewater using ureolytic bacteria and the production of calcium carbonate precipitate for soil stabilization

Rubber wastewater contains variable low pH with a high load of nutrients such as nitrogen, phosphorous, suspended solids, high biological oxygen demand (BOD), and chemical oxygen demand (COD). Ureolytic and biofilm-forming bacterial strains Bacillus sp. OS26, Bacillus cereus OS36, Lysinibacillus macroides ST13, and Burkholderia multivorans DF12 were isolated from rubber processing centres showed high urease activity. Microscopic analyses evaluated the structural organization of biofilm. Extracellular polymeric substances (EPS) matrix of the biofilm of the strains showed the higher abundance of polysaccharides and lipids which help in the attachment and absorption of nutrients. The functional groups of polysaccharides, proteins, and lipids present in EPS were revealed by ATR-FTIR and 1H NMR. A consortium composed of B. cereus OS36, L. macroides ST13, and B. multivorans DF12 showed the highest biofilm formation, and efficiently reduced 62% NH3, 72% total nitrogen, and 66% PO43-. This consortium also reduced 76% BOD, 61% COD, and 68% TDS. After bioremediation, the pH of the remediated wastewater increased to 11.19. To reduce the alkalinity of discharged wastewater, CaCl2 and urea were added for calcite reaction. The highest CaCO3 precipitate was obtained at 24.6 mM of CaCl2, 2% urea, and 0.0852 mM of nickel (Ni2+) as a co-factor which reduced the pH to 7.4. The elemental composition of CaCO3 precipitate was analyzed by SEM-EDX. XRD analysis of the bacterially-induced precipitate revealed a crystallinity index of 0.66. The resulting CaCO3 precipitate was used as soil stabilizer. The precipitate filled the void spaces of the treated soil, reduced the permeability by 80 times, and increased the compression by 8.56 times than untreated soil. Thus, CaCO3 precipitated by ureolytic and biofilm-forming bacterial consortium through ureolysis can be considered a promising approach for neutralization of rubber wastewater and soil stabilization.

A sustainable solution for alleviating hexavalent chromium from water streams using Lactococcus lactis AM99 as a novel Cr(VI)-reducing bacterium

Chromium, extensively used in various industries, poses significant challenges due to its environmental impact. The threat of Cr(VI) causes critical concerns in aquatic ecosystems as a consequence of the fluidity of water. The conventional approach for the treatment of effluents containing Cr(VI) is reducing Cr(VI) to low-noxious Cr(III). This research is related to a Gram positive bacterium newly isolated from tannery effluent under aerobic conditions. To characterize functional groups on the isolate, Fourier transform infrared spectroscopy was utilized. The effect of different factors on Cr(VI) bioreduction was investigated, including temperature, initial Cr(VI) concentration, acetate concentration, and Tween 80 surfactant. Under optimal conditions (37 °C and 0.90 g/L sodium acetate), the bioreduction rate of the isolate, identified as Lactococcus lactis AM99, achieved 88.0 % at 300 mg/L Cr(VI) during 72 h (p < 0.05). It was observed that Cr(VI) bioreduction was enhanced by the acetate in both the quantity and intensity, while Tween 80 had no impact on the reaction. The strain AM99 exhibited remarkable characteristics, notably a marginal decrease in growth at elevated concentrations of hexavalent chromium and an exceptional potential to reduce Cr(VI) even at very low biomass levels, surpassing any prior findings in the associated research. Furthermore, The isolate could tolerate 1400 mg/L Cr(VI) in a solid medium. These distinctive features make the isolate a promising and well-suited candidate for remediating Cr(VI)-polluted environments. Additionally, the impact of biogenic extracellular polymer produced by the strain AM99 on reduction was examined at different temperatures.

Study of the Toxicity and Translocation of Chromium (VI) in Vicia faba Plant

In soil, chromium can be found in two main valence forms: hexavalent Cr (VI) and trivalent Cr (III). In terms of toxicity, the most toxic form to plants is Cr (VI). In the present study, we investigated the impact of Cr (VI) (0, 25, 50, 75 and 100 ppm) on growth, physiological parameters and the translocation kinetics of Cr (VI) in the faba bean plant (Vicia faba L.). The results showed that Cr (VI) negatively affects growth parameters (- 15% to - 72%), tolerance index (- 34.05% to - 64.7%), and reduce the total chlorophyll content (until 40%) compared to control plants without Cr (VI). However, the increase of Cr (VI) concentration in the soil, stimulated the synthesis of sugars (max 6,97 mg/g FM), proteins (max 62.89 µg/mg FM) and proline (max 98.57 µg/mg FM) and increased the electrolyte leakage (+ 2.5% to + 9%) compared to control plants. Cr (VI) concentrations in shoots and roots increased significantly for all Cr (VI) doses applied. The translocation factor results showed that the majority of the Cr (VI) absorbed by the plant is stored in the roots, with a very low bioaccumulation factor, which does not exceed 0.4. The findings show that Cr (VI) negatively affects the morpho-physiological parameters of Vicia faba, the bioaccumulation of organic solutes and the low bioaccumulation factor of Cr (VI) can be considered as a strategy of tolerance to Cr(V).

Removal mechanisms of aqueous Cr(VI) by anaerobic fermentation sludge

After fermentation, activated sludge contains many acid-producing bacteria and their metabolites, which have a good reducing effect. Various active groups (e.g., hydroxyl, amino, carboxyl, and phosphate) on microbial cell surfaces can adsorb heavy metals through complexation or chelation, forming heavy metal precipitates and thereby reducing the toxicity of heavy metals. However, the effects and mechanisms of using sludge after anaerobic fermentation to remove Cr(VI) are unclear, such as the dominance of direct versus indirect biological reduction, the contribution of abiotic effects, and the influence of fermentation conditions. This paper compares Cr(VI) removal in fermented and unfermented sludges. After fermentation for 24 h, 99.9% of the Cr(VI) (50 mg/L) in anaerobic sludge was removed within 7 h, which was twice the rate in unfermented activated sludge. A series of comparative experiments demonstrated that Cr(VI) removal primarily occurred through biological effects (about 92%), which included biological reduction and biosorption. 16SrRNA gene sequencing revealed that Cr(VI) transformation primarily occurred through direct biological reduction, with the related genera being Trichococcus, Acetobacter, Aeromonas, and Tolumonas. Fourier-transform infrared (FTIR) spectroscopy results showed that the C = O and C-O functionalities on sludge were likely involved in the Cr(VI) conversion. Majority of the Cr(VI) in the system was reduced to Cr(III) and existed in the suspension, with a small amount deposited on the sludge surface. The X-ray photoelectron spectroscopy (XPS) results indicated that the majority of Cr was present as reduced Cr(III) on the sludge. These results demonstrate that after fermentation in an aqueous environment, activated sludge is an effective medium for the remediation of Cr(VI). These results are useful for designing a green and sustainable bioreduction system for the remediation of Cr(VI)-polluted water.

Mitigation of chromium-induced phytotoxicity in 28-homobrassinolide treated Trigonella corniculata L. by modulation of oxidative biomarkers and antioxidant system

Chromium (Cr) is one of the toxic heavy metals that disturbs growth and physiological properties of plants. During the current study, Trigonella corniculata L. (Fenugreek) was exposed to different levels of Cr in potted soil. Chromium toxicity reduced fiber, ash, moisture, carbohydrate, protein, fats, and flavonoid content of T. corniculata. Considering the stress relieving effect of 28-homobrassinolide (28-HBR), seeds of T. corniculata were primed with different concentration of 28-HBR i.e., 0, 5, 10, and 20 µmol L-1. Application of 28-HBR reversed the toxic effect of Cr through improvement in activity of antioxidant enzymes like superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Conclusively, 10 µmol L-1 28-HBR increased Cr tolerance in T. corniculata seedlings due to reduction in oxidative stress markers. It is further proposed that 28-HBR is an effective stress ameliorant to relive plants from various abiotic stresses.

Using a Battery of Bioassays to Assess the Toxicity of Wastewater Treatment Plant Effluents in Industrial Parks

Bioassays, as an addition to physico-chemical water quality evaluation, can provide information on the toxic effects of pollutants present in the water. In this study, a broad evaluation of environmental health risks from industrial wastewater along the Yangtze River, China, was conducted using a battery of bioassays. Toxicity tests showed that the wastewater treatment processes were effective at lowering acetylcholinesterase (AChE) inhibition, HepG2 cells' cytotoxicity, the estrogenic effect in T47D-Kbluc cells, DNA damage of Euglena gracilis and the mutagenicity of Salmonella typhimurium in the analyzed wastewater samples. Polycyclic aromatic hydrocarbons (PAHs) were identified as potential major toxic chemicals of concern in the wastewater samples of W, J and T wastewater treatment plants; thus, the potential harm of PAHs to aquatic organisms has been investigated. Based on the health risk assessment model, the risk index of wastewater from the industrial parks along the Yangtze River was below one, indicating that the PAHs were less harmful to human health through skin contact or respiratory exposure. Overall, the biological toxicity tests used in this study provide a good basis for the health risk assessment of industrial wastewater and a scientific reference for the optimization and operation of the treatment process.

Ability of Cupriavidus necator H16 to resist, bioremove, and accumulate some hazardous metal ions in water

Bacterial biomasses are suitable and inexpensive biosorbents for the removal of metal ions. The Gram-negative betaproteobacterium Cupriavidus necator H16 is found in soil and freshwater environments. In this study, C. necator H16 was used to remove chromium (Cr), arsenic (As), aluminum (Al), and cadmium (Cd) ions from water. Minimum inhibition concentration (MIC) values of C. necator to Cr, As, Al, and Cd were found as 76, 69, 341, and 275 mg/L, respectively. The highest rates of Cr, As, Al, and Cd bioremoval were 45, 60, 54, and 78%, respectively. pH levels between 6.0 and 8.0 and an average temperature of 30 °C were optimum for the most efficient bioremoval. Scanning electron microscopy (SEM) images of Cd-treated cells showed that the morphology of the cells was significantly impaired compared to the control. Shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the Cd-treated cell walls also confirmed the presence of active groups. As a result, it can be said that C. necator H16 has a moderate bioremoval efficiency for Cr, As, and Al and a high bioremoval efficiency for Cd.

Treated tannery effluent and its impact on the receiving stream water: physicochemical characterization and cytogenotoxic evaluation using the Allium cepa test

Tanneries are considered some of the most polluting industries due to the heavy use of toxic compounds, most of which are released into water bodies, thus exerting adverse effects on aquatic biota. However, the effects on organisms of treated effluents when released into the natural environment are rarely evaluated. This study aims to assess the physicochemical parameters of a tannery effluent after treatment (TE) at a Common Effluent Treatment Plant as well as the water of the receiving stream and to evaluate cytogenotoxic effects in Allium cepa. Three sampling sites (A: TE discharge point; B: 100 m downstream from site A along the receiving stream; C: 100 m upstream from site A along the stream) were selected. Onion bulbs were exposed to TE (100%, 80%, 60% v/v), water samples from sites B and C, and tap water for 72 h. Chromosomal aberration and mitotic index were analyzed on the root cells of A. cepa. The TE was above the standard limits for ammoniacal nitrogen, COD, and total nitrogen. No cytogenotoxicity was observed in A. cepa exposed to samples from sites A and C. However, the stream water sampled downstream from the TE discharge site significantly reduced the mitotic index, indicating a cytotoxic effect. Therefore, this demonstrates the effects of interactions between the receiving water and the complex chemical mixtures in the TE. The findings thus showed that the toxicity assessment of treated effluents along with the receiving water body would provide valuable and more realistic information about the joint toxicity of chemical pollutants in aquatic environments.

Eco-friendly bioremediation of pollutants from contaminated sewage wastewater using special reference bacterial strain of Bacillus cereus SDN1 and their genotoxicological assessment in Allium cepa

The present study aimed to assess the Bacillus cereus SDN1 native bacterium's ability to clean up contaminated or polluted water. The isolated bacterium was identified by its morphological and biochemical characteristics, which were then confirmed at the genus level. Furthermore, the isolated B. cereus (NCBI accession No: MW828583) was identified genomically by PCR amplifying 16 s rDNA using a universal primer. The phylogenetic analysis of the rDNA sequence was analyzed to determine the taxonomic and evolutionary profile of the isolate of the previously identified Bacillus sp. Besides, B. cereus and the bacterial consortium were treated using sewage wastewater. After 15 days of treatment, the following pollutants or chemicals were reduced: total hardness particles removal varied from 63.33 % to 67.55 %, calcium removal varied from 90 % to 93.33 %, and total nitrate decreased range from 37.77 % to 22.22 %, respectively. Electrical conductivity ranged from 1809 mS/cm to 2500 mS/cm, and pH values ranged from 6.5 to 8.95. The outcome of in-situ remediation results suggested that B. cereus has a noticeable remediation efficiency to the suspended particles. A root tip test was also used to investigate the genotoxicity of treated and untreated sewage-contaminated waters on onion (Allium cepa) root cells. The highest chromosomal aberrations and mitotic inhibition were found in roots exposed to contaminated sewage water, and their results displayed chromosome abnormalities, including disorganized, sticky chain, disturbed metaphase, chromosomal displacement in anaphase, abnormal telophase, spindle disturbances, and binucleate cells observed in A. cepa exposed to untreated contaminated water. The study can thus be applied as a biomarker to detect the genotoxic impacts of sewage water pollution on biota. Furthermore, based on an identified bacterial consortium, this work offers a low-cost and eco-favorable method for treating household effluents.

Cross-habitat distribution pattern of Bacillus communities and their capacities of producing industrial hydrolytic enzymes in Paracel Islands: Habitat-dependent differential contributions of the environment

Bacillus as a predominant genus of enzyme-producing bacteria presents desirable features to fulfill the vast demand of specific industries, whereas the knowledge of the Bacillus communities and their capacities of producing industrial hydrolytic enzymes across the microhabitats of the Paracel Islands is limited. Herein, a total of 193 culturable Bacillus strains belonging to 19 species were isolated across the microhabitats of seawater, sediment, coral and seagrass, covering 39 stations of the Paracel Islands. Each microhabitat displayed its unique species, while the species of Bacillus paramycoides besides being the dominant species with an abundance of 54.94% also was the only species shared by all microhabitats of the Paracel Islands. Of the Bacillus communities, 97.41% of the isolates exhibited the capacity of producing one-or-more types of enzymes with comparatively higher and broader ranges of enzyme activities, including 163 protease-, 27 cellulase-, 118 alginate lyase-, 140 K-carrageenase- and 158 agarose-producing strains. By the correlation analyses of "Bacillus-environmental factors" and "Enzyme-producing Bacillus-environmental factors", the cross-habitat distribution and enzyme-producing capacity pattern of the Bacillus communities were strongly driven by habitat type, and the environmental factors made habitat-dependent differential contributions to that in the Paracel Islands. It's worth noting that the cellulase-producing strain wasn't detected in seagrass due to its survival strategy to prevent cellulose degradation by inhibiting cellulase-producing bacteria, while coral contained more stable microbial metabolic functions to protect against environmental fluctuations. These findings besides providing large quantities of promising enzyme-producing candidates for specific industrial desires, also facilitate the development and utilization of marine microbial resources and the environmental policy- and/or law-making according to environmental features across the microhabitats of the Paracel Islands.

Brassinosteroid Supplementation Alleviates Chromium Toxicity in Soybean (Glycine max L.) via Reducing Its Translocation

Chromium (Cr) phytotoxicity severely inhibits plant growth and development which makes it a prerequisite to developing techniques that prevent Cr accumulation in food chains. However, little is explored related to the protective role of brassinosteroids (BRs) against Cr-induced stress in soybean plants. Herein, the morpho-physiological, biochemical, and molecular responses of soybean cultivars with/without foliar application of BRs under Cr toxicity were intensely investigated. Our outcomes deliberated that BRs application noticeably reduced Cr-induced phytotoxicity by lowering Cr uptake (37.7/43.63%), accumulation (63.92/81.73%), and translocation (26.23/38.14%) in XD-18/HD-19, plant tissues, respectively; besides, improved seed germination ratio, photosynthetic attributes, plant growth, and biomass, as well as prevented nutrient uptake inhibition under Cr stress, especially in HD-19 cultivar. Furthermore, BRs stimulated antioxidative defense systems, both enzymatic and non-enzymatic, the compartmentalization of ion chelation, diminished extra production of reactive oxygen species (ROS), and electrolyte leakage in response to Cr-induced toxicity, specifically in HD-19. In addition, BRs improved Cr stress tolerance in soybean seedlings by regulating the expression of stress-related genes involved in Cr accumulation, and translocation. Inclusively, by considering the above-mentioned biomarkers, foliar spray of BRs might be considered an effective inhibitor of Cr-induced damages in soybean cultivars, even in Cr polluted soil.

Effective bioremediation of pulp and paper mill wastewater using Bacillus cereus as a possible kraft lignin-degrading bacterium

The effective degradation of KL from paper mill effluent is an important for environmental safety. This research is primarily concerned with the identification of KL-degrading Bacillus cereus from activated sludge and their possible use for the degradation of Kraft lignin (KL). This strain was involved in the production of lignin peroxidase-LiP (3.20 U/mL), manganese peroxidase-MnP (20.36 U/mL), and laccase (21.35 U/mL) enzymes, which were responsible for high KL degradation (89%) and decolorization (40%) at 1000 mg/L KL in 3 days. The SEM-EDS, UV-Vis, FTIR, and GC-MS analysis were used to analyze the bacterial cell and KL interactions to trace the KL degradation process. The significant reduction of pollutants (KL-72.5%, color-62.0%, COD-45.05%) and reduction in toxicity (80%) of bacterial-treated effluent indicated that B. cereus has the potential to be used in the degradation of pollutants from paper mill effluents.

Application of exogenous glutathione decreases chromium translocation and alleviates its toxicity in soybean (Glycine max L.)

Chromium is considered one of the most severe toxic elements affecting agriculture. Soybean seedlings under chromium stress were treated with glutathione and buthionine sulfoximine. The effects of exogenous glutathione on the physiological effects of two different chromium-resistant soybean seedlings and the expression levels of expression levels related genes were studied. This study tested the seedling weight and SPAD values, detected enzymatic antioxidants (i.e., superoxide dismutase, peroxidase, catalase, catalase, ascorbate peroxidase), and non-enzymatic antioxidants (i.e., glutathione, proline, soluble sugars, and soluble phenols) that attenuate chromium-induced reactive oxygen species, and quantified several genes associated with glutathione-mediated chromium stress. The results showed that exogenous glutathione could improve the physiological adaptability of soybean seedlings by regulating photosynthesis, antioxidant, and related enzyme activities, osmotic system, the compartmentalization of ion chelation, and regulating the transcription level of related genes, thereby increasing the chromium accumulation of soybean seedlings, enhancing the tolerance of chromium stress, and reducing the toxicity of chromium. Overall, the application of glutathione alleviates chromium toxicity in soybeans, and this strategy may be a potential farming option for soybean bioremediation in chromium-contaminated soils.

Characterization of biofilm formation and reduction of hexavalent chromium by bacteria isolated from tannery sludge

Biofilm formation ability of bacteria makes them potential in the field of tannery effluent treatment. However, the hazardous nature of effluent and environmental conditions may disturb the biofilm formation ability of bacteria which ultimately affects their effluent treatment efficiency. Accordingly, we isolated and characterized biofilm-forming bacteria Bacillus vallismortis (MT027009), Bacillus haynesii (MT027008), and Alcaligenes aquatilis (MT027005) from tannery sludge and examined them for biofilm formation under variable environmental conditions. Biofilm formation in tryptic soy broth (TSB) at different incubation times (24-120 h) revealed that the biofilm formation activity of the strain B. haynesii was not affected by incubation time, whereas the increase in biofilm formation was observed in the case of B. vallismortis (28 %) and A. aquatilis (52 %) after 48 h. The medium pH (pH 5.0-9.0) had a limited effect on biofilm formation except in the case of A. aquatilis at pH 5.0 (94 %) and pH 9.0 (80 %). Furthermore, compared to the controls (only TSB), the strains B. vallismortis, B. haynesii, and A. aquatilis showed enhanced biofilm formation in undiluted tannery effluent (28, 33, and 21 %) and 25 mg L^-1 Cr(VI) (23 %, 48 % 32 %). The biofilm structure was influenced by Cr(VI) as revealed by scanning electron microscopy (SEM) analysis. The results of Cr(VI) bioreduction studies suggest that bacterial biofilm (60-99 %) has a greater potential to remove Cr(VI) than planktonic cells (43-94 %). The results of the study provide important data on biofilm formation by indigenous bacteria in effluent environment conditions, making them potential isolates for tannery effluent treatment.

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.

Statistical optimization of chromium (VI) reduction using response surface methodology (RSM) by newly isolated Stenotrophomonas sp. (a novel strain)

Isolation of Microorganisms capable of reducing toxic chromium (VI) into less toxic one (Cr (III)) has been given attention due to their significance in bioremediation of the contaminated sites. In the present study, Stenotrophomonas sp. Crt94-4A an isolated strain from tannery wastewater and identified genetically by 16s rRNA gene sequencing was able to grow at concentrations up to 354 mg/L of Cr (VI). The results revealed 1% (w/v) NaCl, 2% (v/v) (2 × 10⁶ CFU) inoculum size, and PH 7 in culture containing glucose and peptone as carbon and nitrogen sources respectively were the best conditions for Cr (VI) reduction. Statistical optimization was performed using Plackett-Burman design where peptone, inoculum size, and NaCl had significant effects on Cr (VI) reduction which were tested by three factors Box-Behnken design (BBD) to determine their correlation. The reduction capacity of Cr (VI) by Stenotrophomonas Sp. Crt94-4A was increased from 82, 55, and 23 to 96, 76, and 45% at 88.5, 177 and 354 mg/L of Cr (VI) respectively, which make this strain a good candidate for bioremediation of Cr (VI).

A Bacillus and Lysinibacillus sp. bio-augmented Festuca arundinacea phytoremediation system for the rapid decontamination of chromium influenced soil

Phytoremediation as an efficient and eco-friendly soil detoxification method has received widespread attention. In this study, two newly screened Chromium (Cr) reducing strains (Bacillus sp. AK-1 and Lysinibacillus sp. AK-5) were used to remediate Cr contaminated soil in conjunction with the application of hyperaccumulator tall fescue (Festuca arundinacea), thus establishing a soil Cr decontamination system. In this system, soil urease and dehydrogenase activities were increased, the malondialdehyde (MDA) contents in leaves of tall fescue were significantly decreased, while glutathione (GSH) contents increased. In terms of Cr fractions, the proportion of acetic acid extractable Cr decreased by 12.82-20.00% in treatment groups, respectively, compared with CK, while residual Cr increased by 9.41-22.37%. Moreover, biomass, root length and shoot length of tall fescue in treatment groups increased by 80.77-139.74%, 60.85-68.04%, 7.06-27.10%, respectively. In addition, the root system of tall fescue accumulated 303.887-372.167 mg kg^-1 of Cr, and the aboveground part accumulated 16.289-19.289 mg kg^-1 of Cr. Therefore, the application of strains AK-1 and AK-5 reduced the toxicity of Cr to plants and greatly increased plant accumulation potential, which indicated that AK-1 and AK-5 could improve removal efficiency of phytoremediation in Cr contaminated soil by reducing its bio-toxicity and promoting growth of tall fescue growth.

Luteolin mitigates potassium dichromate-induced nephrotoxicity, cardiotoxicity and genotoxicity through modulation of Kim-1/Nrf2 signaling pathways

Environmental and occupational exposure to chromium compounds has become potential aetiologic agent for kidney disease with excessive generation of free radicals, apoptosis, and inflammatory. These pathophysiologic mechanisms of potassium dichromate (K₂ Cr₂ O₇ ) have been well correlated with nephrotoxicity and cardiotoxicity. The cardioprotective and nephroprotective effects of Luteolin, a known potent antioxidant were evaluated in this study with 40 healthy rats in four experimental groups: Group A (normal saline), Groups B (30 mg/kg K₂ Cr₂ O₇ ), Group C (Luteolin 100 mg/kg and K₂ Cr₂ O₇ 30 mg/kg), and Group D (Luteolin 200 mg/kg and K₂ Cr₂ O₇ 30 mg/kg), respectively. Markers of antioxidant defense system, oxidative stress, blood pressure and micronucleated polychromatic erythrocytes (MnPEs), immunohistochemistry of Kidney, injury molecule (Kim-1), nuclear factor erythroid 2-related factor 2 (Nrf2), and cardiac troponin I were determined. Administration of K₂ Cr₂ O₇ increased blood pressure parameters in systolic, diastolic and mean arterial blood pressures, markers of oxidative stress, and frequency of micronucleated polychromatic erythrocytes, together with reduction in serum nitric oxide level. Renal Kim-1 and cardiac troponin I expressions were higher, but lower expressions of renal and cardiac Nrf2 were recorded with immunohistochemical analysis. Pre-treatment with Luteolin restored blood pressure parameters, with concomitant reduction in oxidative stress indicators, augmented antioxidant mechanisms and serum Nitric oxide level, lowered the expressions of Kim-1, cardiac troponin I and up-regulated of both cardiac and renal Nrf2, reduced the frequency of micronucleated polychromatic erythrocytes. Taken together, this study therefore demonstrates the cardioprotective, nephro protective and antigenotoxic effects of Luteolin through antioxidantive and radical scavenging mechanisms.

Multi-Strain Tropical Bacillus spp. as a Potential Probiotic Biocontrol Agent for Large-Scale Enhancement of Mariculture Water Quality

Aquaculture is suffering from long-term water eutrophication in intensive models, whereas the knowledge of multi-strain/specie for improving water quality is extremely limited. Herein, we aimed to develop multi-strain tropical Bacillus spp. as a potential probiotic biocontrol agent for large-scale enhancement of mariculture water quality. Given the practical application, the optimum multi-strain tropical Bacillus spp. (B. flexus QG-3, B. flexus NS-4, and B. licheniformis XCG-6 with the proportion 5: 5: 4) as a probiotic biocontrol agent was screened and obtained, which effectively improved water quality by removing chemical oxygen demand (COD), ammonia-nitrogen, and nitrate and significantly inhibited Vibrio spp. even at relatively low bacterial concentrations (104 CFU/ml) in artificial feed wastewater and large-scale shrimp aquaculture ponds. More importantly, we found that the initial proportion of these three Bacillus sp. strains of multi-strain tropical Bacillus spp. markedly affected the final purification effects, whereas the initial concentration of that only influenced the purification rates at the early stage (0-48 h) instead of final purification effects. We reason that this multi-strain tropical Bacillus spp. as a good probiotic biocontrol agent could perform multiple actions, such as COD-degrading, nitrifying, denitrifying, and antagonistic actions, for large-scale enhancement of tropical aquaculture water. Additionally, the multi-strain tropical Bacillus spp. was safe for shrimp and could be stored for at least 240 days in spore form at room temperature. This multi-strain probiotic biocontrol agent may facilitate its adoption for further marine recirculating aquaculture system development and large-scale commercial application.

Cytotoxic and genotoxic assessment of agricultural soils from an industrial region

Industrial effluents contain hazardous substances that can be a serious threat to the agriculture and human health. In the present study, the cytotoxic and genotoxic impacts of agricultural soil from the industrial area of Dera Bassi (Punjab, India) have been evaluated. Assays such as defects in DNA repair in K-12 mutants of Escherichia coli and chromosomal aberrations in Allium cepa were used to estimate the acute toxicity and chromosomal mutagenesis, respectively. Atomic absorption spectrometry and GC-MS analysis revealed contamination of the soil with high concentrations of heavy metals and organic compounds, respectively. Dichloromethane extract of site I soil sample caused maximum damage to 40 μL mL^-1 DNA repair defective mutants and showed 38 and 49% survival in lexA and recA mutants, respectively, which was least among all the sites. In A. cepa test, an inverse relationship between soil extract concentration and the mitotic index was observed. Exposure of growing roots of A. cepa to soil extracts induced chromosomal abnormalities and alterations in mitotic phases in root tip cells. The study concludes that agricultural sites near the industrial area were contaminated with genotoxic and mutagenic compounds. Hence, adequate measures should be taken to reduce the toxicity of industrial effluents discharged onto the agricultural fields.

Menadione sodium bisulfite alleviated chromium effects on wheat by regulating oxidative defense, chromium speciation, and ion homeostasis

Menadione sodium bisulfite (MSB) is a crucial growth regulator mediating plant defense response. MSB-mediated regulation of defense mechanisms in wheat under chromium (Cr) toxicity has not been reported in the literature. Therefore, the present study was undertaken to appraise the efficacy of exogenous MSB on circumventing Cr phytotoxic effects on wheat. We also compared the effects of water-soluble MSB with that of water-insoluble menadiol diacetate (MD). The levels used in the present investigation for MSB and MD were 100 and 200 mg L-1. Wheat plants grown in soil contaminated with 25 mg kg-1 Cr in the form of K2Cr2O7 showed a notable reduction in growth, chlorophyll molecules, relative water contents, grain yield, total soluble sugars, phenolics, flavonoids, ascorbic acid, activities of antioxidant enzymes (SOD, POD, CAT), and uptake of essential nutrients (K, P, and Ca). Cr toxicity caused a noticeable accretion in total free amino acids, proline, malondialdehyde, H2O2, O2•-, relative membrane permeability, methylglyoxal contents, activities of enzymes (lipoxygenase, glutathione-S-transferase, and ascorbate peroxidase), nitric oxide and H2S contents, glutathione and oxidized glutathione contents, total Cr contents, and Cr6+ and Cr3+ accumulation. MSB application significantly reduced lipid peroxidation, ROS overproduction, methylglyoxal levels, total Cr contents, and maintained higher Cr3+:Cr6+ ratio in aerial parts. Besides, Cr-mediated inhibition in essential nutrient uptake was significantly circumvented by exogenous MSB. Consequently, MSB enhanced wheat growth by lessening oxidative damage, total Cr contents in aerial parts, and strengthening antioxidant enzyme activities. MD was not effective in mediating defense responses in wheat under Cr toxicity.

Hexavalent chromium reducing bacteria: mechanism of reduction and characteristics

As a common heavy metal, chromium and its compounds are widely used in industrial applications, e.g., leather tanning, electroplating, and in stainless steel, paints and fertilizers. Due to the strong toxicity of Cr(VI), chromium is regarded as a major source of pollution with a serious impact on the environment and biological systems. The disposal of Cr(VI) by biological treatment methods is more favorable than traditional treatment methods because the biological processes are environmentally friendly and cost-efficient. This review describes how bacteria tolerate and reduce Cr(VI) and the effects of some physical and chemical factors on the reduction of Cr(IV). The practical applications for Cr(VI) reduction of bacterial cells are also included in this review.

Bioaccumulation of fluoride from aqueous system and genotoxicity study on Allium cepa using Bacillus licheniformis

Removal of fluoride (F^-) was performed using a novel bacterium isolated from F^- contaminated soil collected from Pappireddipatti block of Dharmapuri District in Tamil Nadu, India. Impact of changing variables for the removal of F^- from synthetic medium at different concentrations of carbon and nitrogen sources (0.5, 1.0 and 1.5 g) was studied with bio inoculants of the bacterial strain (PPR8). The effects of different environmental parameters viz., pH (5.0-9.0) and temperature (25-45 °C) on the biosorption of F^- biosorption were also evaluated. The strain PPR8 was identified as Bacillus licheniformis through 16S rRNA sequencing and phylogenetic analysis. Bioaccumulation of F^- in the bacterial cells was confirmed by FTIR, SEM and TEM-EDAX and almost 97% of F^- removal was established. To test the potential applicability of the bacterium, the bioreactor study was carried out with F^- contaminated groundwater collected from the contaminated area. Furthermore, the treated and untreated F^- contaminated waters were used to evaluate the genotoxicity on the root cells of onion (Allium cepa) by root tip assay. The experimental results proved that the significant removal of F^- by Bacillus licheniformis PPR8 (KX646393) and it could be used as a potential adsorbent in removing F^- from contaminated ground waters.

Community Structure of Protease-Producing Bacteria Cultivated From Aquaculture Systems: Potential Impact of a Tropical Environment

Protease-producing bacteria play vital roles in degrading organic matter of aquaculture system, while the knowledge of diversity and bacterial community structure of protease-producing bacteria is limited in this system, especially in the tropical region. Herein, 1,179 cultivable protease-producing bacterial strains that belonged to Actinobacteria, Firmicutes, and Proteobacteria were isolated from tropical aquaculture systems, of which the most abundant genus was Bacillus, followed by Vibrio. The diversity and relative abundance of protease-producing bacteria in sediment were generally higher than those in water. Twenty-one genera from sediment and 16 genera from water were identified, of which Bacillus dominated by Bacillus hwajinpoensis in both and Vibrio dominated by Vibrio owensii in water were the dominant genera. The unique genera in sediment or water accounted for tiny percentage may play important roles in the stability of community structure. Eighty V. owensii isolates were clustered into four clusters (ET-1-ET-4) at 58% of similarity by ERIC-PCR (enterobacterial repetitive intergenic consensus-polymerase chain reaction), which was identified as a novel branch of V. owensii. Additionally, V. owensii strains belonged to ET-3 and ET-4 were detected in most aquaculture ponds without outbreak of epidemics, indicating that these protease-producing bacteria may be used as potential beneficial bacteria for wastewater purification. Environmental variables played important roles in shaping protease-producing bacterial diversity and community structure in aquaculture systems. In sediment, dissolved oxygen (DO), chemical oxygen demand (COD), and salinity as the main factors positively affected the distributions of dominant genus (Vibrio) and unique genera (Planococcus and Psychrobacter), whereas temperature negatively affected that of Bacillus (except B. hwajinpoensis). In water, Alteromonas as unique genus and Photobacterium were negatively affected by NO₃ ^--N and NO₂ ^--N, respectively, whereas pH as the main factor positively affected the distribution of Photobacterium. These findings will lay a foundation for the development of protease-producing bacterial agents for wastewater purification and the construction of an environment-friendly tropical aquaculture model.

An experimental approach for the utilization of tannery sludge-derived Bacillus strain for biosorptive removal of Cr(VI)-contaminated wastewater

Biosorption efficacy of Bacillus strain DPAML065, isolated from the tannery sludge, was appraised for the removal of toxic hexavalent chromium (VI) ions from synthetic wastewater. Effects of the process variable on biosorbent surface by variation in pH, metal Cr(VI) concentration and retention time were examined using batch experiments. The isolated Bacillus strain biosorbent was studied for its morphology and surface chemistry through FE-SEM, EDX and FTIR. It discloses that, the reduction mechanism of Cr(VI) during the process is mainly attributed to precipitation in addition to the functional groups (such as -COOH, -OH, C-O, P=O) present on the cellular matrix of Bacillus. Biochemical tests and 16s rRNA sequencing were also performed to identify the biosorbent at the genus level. A 95% Cr(VI) removal efficiency was procured by Bacillus strain DPAML065 biosorbent at pH 6, incubation period 24 h, 80 mg/L initial feed concentration and operational temperature 35 °C. Equilibrium behaviour of chromium binding follows the Langmuir isotherm model (R² = 0.968) with an adsorption capacity of 106.38 mg/g. Kinetic modelling disseminates that biosorption of Cr(VI) ions by Bacillus strain DPAML065 obeyed pseudo-second-order model (R² = 0.984) rather than the pseudo-first-order model. Concisely, the results indicate that the Bacillus strain DPAML065 is a potential, economically feasible and eco-friendly biosorbent which can be effectively used for removal of chromium (VI) from wastewater.

Decolourization of textile effluent using native microbial consortium enriched from textile industry effluent

A robust and efficient treatment process is required to address the problem of residual colour and avoid expensive post-treatment steps while dealing with textile effluents. In the present work, a novel microbial consortium enriched from textile effluent was used to optimize the process of decolourization under extreme conditions with minimum inputs. With PreTreatment Range (PTR) effluent as a carbon source and only 0.5 g/L yeast extract as external input, the process enabled 70-73% colour reduction (from 1910-1930 to 516-555 hazen) in dyeing unit wastewater. Unhindered performance at higher temperatures (30 °C-50 °C) and wide pH range (7-12) makes this process highly suitable for the treatment of warm and extremely alkaline textile effluents. No significant difference was observed in the decolourization efficiency for effluents from different batches (Colour: 1647-4307 hazen; pH-11.5-12.0) despite wide variation in nature and concentration of dyes employed. Long term (60 days) continuous mode performance monitoring at hydraulic retention time of 48 h in lab-scale bioreactor showed consistent colour (from 1734-1980 to 545-723 hazen) and chemical oxygen demand (1720-2170 to 669-844 mg/L) removal and consistently neutral pH of the treated water. Present study thus makes a significant contribution by uncovering the ability of native microbial consortium to reliably treat dye laden textile wastewater without any dilution or pre-treatment and with minimum external inputs. The results ensure easy applicability of this indigenously developed process at the industrial scale.

Microremediation of tannery wastewater by siderophore producing marine bacteria

The present study evaluated the microremediation potential of nine siderophore producing marine bacteria for hazardous raw tannery wastewater from common effluent treatment plant (CETP). Most of the pollutants detected in the wastewater were diminished after the bioremediation process. Further, among the three potent isolates selected for aerobic and anaerobic bioremediation study, Marinobacter hydrocarbonoclasticus demonstrated the highest bioremediation aerobically with a reduction in chromium (88%), sulphate (71%), phosphate (68%) and nitrate (57%). Notably, Nitratireductor kimnyeongensis could attack the effluent under both aerobic and anaerobic conditions as substantiated by statistically significant (p < .05) reduction in the pollutants [chromium (85%), sulphate (63%), Chemical Oxygen Demand (COD) (69%), phosphate (76%)]. From the study it is evident that the pollutant load reduction was achieved under both aerobic and anaerobic conditions, however, aerobic environment was more effective in reducing chromium, Biochemical Oxygen Demand (BOD), sulphate, nitrate and phosphate. The bioremediation efficiency was further confirmed by the bioassay experiments with plant and animal models where higher seed germination, greater plant length and biomass, as well as improved survival rate of Artemia nauplii for bioremediated wastewater was observed as compared to the untreated effluent indicating a significant reduction in toxicity. The results for simultaneous removal of multiple-toxicants thus signify effectiveness and ease of using the robust properties of these marine bacterial strains suggesting their potential application for bioremediation. Hence this could pave a promising way for an environment-friendly and economically feasible clean-up strategy for safer disposal of tannery wastewater.

Biosorption of Cr(VI) by Halomonas sp. DK4, a halotolerant bacterium isolated from chrome electroplating sludge

This study evaluated Cr(VI) biosorption by a halotolerant gram-negative bacterium Halomonas sp. DK4 isolated from chrome electroplating sludge. The bacterium could withstand high concentrations of Cr(VI) exhibiting a minimal inhibitory concentration (MIC) of 250 mg/L. Plackett-Burman design confirmed glucose, KH₂PO₄, NaCl, inoculum size, and initial Cr(VI) concentration as significant variables influencing the Cr(VI) removal ability of the bacterium. The suspended culture of Halomonas sp. DK4 was able to remove 81% (100 mg/L) of Cr(VI) in optimized MSM medium from aqueous solutions within 48 h. The bacterium also removed 59% Cr(VI) in the presence of 15% NaCl concentration within 72 h. The main mechanism involved in Cr(VI) removal by Halomonas sp. DK4 was determined to be biosorption which was best explained using the Langmuir isotherm model, wherein the maximum adsorption of 150.7 mg/g was observed under equilibrium conditions. Kinetic studies reveal that chemisorption of Cr(VI) by Halomonas sp. DK4 was a rate-limiting process which followed pseudo-second-order kinetics (R² = 0.99). Bacterial biomass exhibited maximum adsorption of 70.3% Cr(VI) at an initial concentration of 100 mg/L under optimal conditions. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the presence of hydroxyl, carboxyl, amide, and phosphate groups on the bacterial surface which may be involved in Cr(VI) adsorption. Scanning electron microscopy coupled energy dispersive X-ray (SEM-EDX) analysis revealed morphological changes in the bacterial cell and accumulation of Cr(VI) on the cell surface. These results suggest the potential application of Halomonas sp. DK4 in the removal of Cr(VI) from saline chromium-containing industrial wastewaters.

Insights into the resources generation from pulp and paper industry wastes: Challenges, perspectives and innovations

Pulp and paper industry is swiftly budding to fulfill industrial needs and with the growth of this industry, a large amount of waste has also generated which includes biological sludge generated from the wood digestion process, fly ash accumulation and lime mud produced in chemical reagent recovery circuit. There are many health hazards associated with generated wastes and this waste material can be utilized in sustainable ways to generate useful resources through technological innovations. This review highlights a few useful aspects of waste conversion to resources like the production of green energy, sorbent development, and clinker preparation. The generation of resources from such wastes is a revolutionary and innovative concept for sustainable development including valorization of the generated waste to integrate pulp and paper industry with biorefinery. This review paper focuses on the sustainable utilization of waste from such industry along with its efficiency and future challenges.

Chromium-Induced Reactive Oxygen Species Accumulation by Altering the Enzymatic Antioxidant System and Associated Cytotoxic, Genotoxic, Ultrastructural, and Photosynthetic Changes in Plants

Chromium (Cr) is one of the top seven toxic heavy metals, being ranked 21st among the abundantly found metals in the earth’s crust. A huge amount of Cr releases from various industries and Cr mines, which is accumulating in the agricultural land, is significantly reducing the crop development, growth, and yield. Chromium mediates phytotoxicity either by direct interaction with different plant parts and metabolic pathways or it generates internal stress by inducing the accumulation of reactive oxygen species (ROS). Thus, the role of Cr-induced ROS in the phytotoxicity is very important. In the current study, we reviewed the most recent publications regarding Cr-induced ROS, Cr-induced alteration in the enzymatic antioxidant system, Cr-induced lipid peroxidation and cell membrane damage, Cr-induced DNA damage and genotoxicity, Cr-induced ultrastructural changes in cell and subcellular level, and Cr-induced alterations in photosynthesis and photosynthetic apparatus. Taken together, we conclude that Cr-induced ROS and the suppression of the enzymatic antioxidant system actually mediate Cr-induced cytotoxic, genotoxic, ultrastructural, and photosynthetic changes in plants.

Chromium Bioaccumulation and Its Impacts on Plants: An Overview

Chromium (Cr) is an element naturally occurring in rocky soils and volcanic dust. It has been classified as a carcinogen agent according to the International Agency for Research on Cancer. Therefore, this metal needs an accurate understanding and thorough investigation in soil-plant systems. Due to its high solubility, Cr (VI) is regarded as a hazardous ion, which contaminates groundwater and can be transferred through the food chain. Cr also negatively impacts the growth of plants by impairing their essential metabolic processes. The toxic effects of Cr are correlated with the generation of reactive oxygen species (ROS), which cause oxidative stress in plants. The current review summarizes the understanding of Cr toxicity in plants via discussing the possible mechanisms involved in its uptake, translocation and sub-cellular distribution, along with its interference with the other plant metabolic processes such as chlorophyll biosynthesis, photosynthesis and plant defensive system.

Bioreduction of hexavalent chromium using a novel strain CRB-7 immobilized on multiple materials

In this study, a novel Cr(VI) tolerant strain CRB-7 identified as Bacillus sp., was isolated and characterized for its high Cr(VI) reduction. The strain CRB-7 grew well and effectively reduced Cr(VI) under various conditions including pH (7-9), temperature (30-40 °C) and Cr(VI) concentrations (50-250 mg L^-1). It almost completely reduced 120 mg L^-1 Cr(VI) within 48 h under optimized condition of pH 7 and 37 °C. Further characterization by SEM-EDS and FTIR analyses indicated Cr(VI) removal mechanism of CRB-7 was predominately via bioreduction with little amount of bioadsorption. Furthermore, the strain CRB-7 based immobilized biobeads were successfully synthesized using five different porous materials as bacterial loading carrier respectively to ascertain the optimal immobilization biocomposite for Cr(VI) removal. CRB-7 cells immobilized with 3% sodium alginate (SA) and 5% humic acid (HA) exhibited the highest Cr(VI) removal efficiency. Moreover, immobilized biobeads have the advantages over free cells in being more stable and easier to reuse. High Cr(VI) reducing ability of the free and immobilized CRB-7 cells suggest the strain CRB-7, especially the B-HA-SA biocomposite is promising for remediating Cr(VI)-contaminated sites.

Chromate tolerance and removal of bacterial strains isolated from uncontaminated and chromium-polluted environments

Investigation of bacterial chromate tolerance has mostly focused on strains originating from polluted sites. In the present study, we isolated 33 chromate tolerant strains from diverse environments harbouring varying concentrations of chromium (Cr). All of these strains were able to grow on minimal media with at least 2 mM hexavalent chromium (Cr(VI)) and their classification revealed that they belonged to 12 different species and 8 genera, with a majority (n = 20) being affiliated to the Bacillus cereus group. Selected B. cereus group strains were further characterised for their chromate tolerance level and the ability to remove toxic Cr(VI) from solution. A similar level of chromate tolerance was observed in isolates originating from environments harbouring high or low Cr. Reference B. cereus strains exhibited the same Cr(VI) tolerance which indicates that a high chromate tolerance could be an intrinsic group characteristic. Cr(VI) removal varied from 22.9% (strain PCr2a) to 98.5% (strain NCr4). Strains NCr1a and PCr12 exhibited the ability to grow to the greatest extent in Cr(VI) containing media (maximum growth of 65.3% and 64.9% relative to that in the absence of Cr(VI), respectively) accompanied with high chromate removal activity (73.7% and 74.4%, respectively), making them prime candidates for the investigation of chromate tolerance mechanisms in Gram-positive bacteria and Cr(VI) bioremediation applications.

Isolation and characterization of lignin-degrading bacterium Bacillus aryabhattai from pulp and paper mill wastewater and evaluation of its lignin-degrading potential

This study reports the degradation and decolourization capability of a manganese peroxidase enzyme producing bacterium isolated from pulp and paper mill wastewater. The isolate was identified as Bacillus aryabhattai based on biochemical analysis and 16S rRNA gene sequencing. The strain was designated MG966493. This bacterium was able to reduce 67% and 54% colour and lignin, respectively, from the pulp and paper mill wastewater after 144 h of treatment at 32 °C, pH 7.6 and 120 rpm. Further, FT-IR analysis showed that during the lignin degradation process a number of metabolites were produced comprising different functional groups such as carbonyl (C=C), carboxyl (-COOH), alkene (C=C), amines (-NH₂), sulphonic (-SO₃) and nitro (-NO₂). In addition, the SEM analysis showed that the bacterial cells exposed to pulp and paper mill wastewater have rough surfaces with reduced size as compared to the unexposed cells with smooth surfaces. This study concluded that the isolated bacterium B. aryabhattai has significant potential for the bioremediation of pulp and paper mill wastewater and thus, can be applied for their treatment at an industrial scale.

Alleviation of hexavalent chromium by using microorganisms: insight into the strategies and complications

Excessive industrialization and anthropogenic activities have resulted in widespread prevalence of heavy metals including hexavalent chromium in the environment. In addition to toxic properties, Cr(VI) possesses high stability and mobility, which in total makes it included in the list of priority heavy metals; thus it needs to be managed urgently. Among different methods available for remediation of Cr(VI), bioremediation is considered as one of the sustainable methods which could effectively be utilized for controlling Cr(VI) pollution. In this aspect, the treatment of Cr(VI)-containing wastewater originating from industries is noteworthy. The present review thus is an attempt to present a systematic overview dealing with studies on remediation of hexavalent chromium by using microorganisms and their application in treatment of Cr(VI)-containing industrial wastewaters. Various factors affecting the Cr(VI) removal and methods to enhance the bio-treatment are highlighted, which might act as a basis for researchers developing Cr(VI) bioremediation techniques.

Effective bioremediation and toxicity assessment of tannery wastewaters treated with indigenous bacteria

This study evaluated the bioremediation capacity of indigenous bacteria isolated from tannery sludge for two different tannery wastewaters collected from Kanpur and Chennai. To identify bacteria which can efficiently degrade a mixture of different pollutants, the isolates were grown in hazardous 100% tannery wastewaters. The reductions in toxicants such as chromium, sulphate, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater were analysed post-bioremediation. Amongst the isolates, Citrobacter freundii was able to reduce the concentration of multiple toxicants such as chromium by 73% and sulphate was reduced by 68% bringing down the level much below the permissible limit stipulated by Bureau of Indian Standards (BIS). Notably, the organic load characterized by BOD and COD was also lowered by 86 and 80%, respectively. The indigenous isolates, not only bioremediated the Kanpur effluent but, also significantly detoxified the Chennai effluent having higher toxicant load. An interesting observation made during the study was better survival and growth along with the development of appendages of Artemia nauplii in the treated wastewaters which thus further confirmed reduction in toxicity of the effluents. The results thus demonstrate that the tested indigenous strains are promising for bioremediation of tannery wastewater and effectively improve the water quality for safe discharge.