Efficacy of bacterial consortium-AIE2 for contemporaneous Cr(VI) and azo dye bioremediation in batch and continuous bioreactor systems, monitoring steady-state bacterial dynamics using qPCR assays

Biodegradation of phenanthrene-Cr (VI) co-contamination by Pseudomonas aeruginosa AO-4 and characterization of enhanced degradation of phenanthrene

Microorganisms capable of simultaneously remediating heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution hold significant importance in bioremediation efforts. In this study, we investigated the ability of Pseudomonas aeruginosa AO-4 to simultaneously degrade phenanthrene (PHE) and reduce Cr (VI). Specifically, it has the ability to reduce 100 % of Cr (VI) (30 mg/L) while degrading 43.8 % of PHE (50 mg/L). In batch experiments, it was observed that the presence of Cr (VI) can enhance the degradation of PHE by strain AO-4. The solubility of PHE in soluble extracellular polymeric substances (S-EPS) was found to be related to the initial concentration of Cr (VI), which could explain why Cr (VI) promotes the degradation of PHE. Additionally, XPS analysis confirmed that Cr (VI) was reduced to Cr (III) with S-EPS produced by Pseudomonas aeruginosa AO-4. GC-MS analysis was conducted to analyze the degradation metabolites of phenanthrene, di(2-ethylhexyl) phthalate and 2TMS derivatives of salicylic acid were detected, indicating that Pseudomonas aeruginosa AO-4 is capable of degrading phenanthrene through two distinct pathways. These findings demonstrate the potential of Pseudomonas aeruginosa AO-4 in the treatment of co-contamination scenarios involving PAHs and HMs.

Simultaneous conversion of chromium and malachite green coexists in halophilic bacterium Halomonas xianhensis SUR308 isolated from a solar saltern

Many industries are known to use heavy metals like chromium (Cr) to fix dyes in the fabrication processes and malachite green (MG) as colorant. Alkalinity, elevated temperature, or salinity of the industrial effluents makes conventional physicochemical removal of MG and hexavalent chromium [Cr(VI)] more difficult to apply and demands to perceive potential cost-effective and environment-friendly treatment methods to eliminate or convert them into less toxic compounds. Here, we report simultaneous removal and bioconversion of MG and Cr(VI) by a halophilic biofilm-forming bacterium Halomonas xianhensis SUR308. It can efficiently produce exopolysaccharides as extracellular polymeric substances (EPS) and form biofilm under oxygen limiting condition. The reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] is about 100%, and 95% after 84 h of growth in shaken and stagnant culture, respectively. The strain completely decolorizes MG after 48 h of growth in shaken culture. Furthermore, we found that strain SUR308 can efficiently detoxify chromium by reduction and degrades MG via producing various intermediate products simultaneously. Most interestingly, such conversions can also take place in alkaline environment and in environment where substantial amount of salt is present. These unique features of strain SUR308 make it suitable for the simultaneous remediation of toxic heavy metals and hazardous dye even from the environment having higher pH and salinity. The detail molecular mechanism of the bioconversion with its application in open environment would be the future research focus for bioprospecting strain SUR308.

Multi-biological combined system: A mechanistic approach for removal of multiple heavy metals

In this work, interactions of diverse fungal species by the manipulation of cell concentrations has been utilized as the driving feature for the removal of hazardous multi-metals from the aqueous solutions. This study is focused on the exploitation of internal structures of microbes as a repository of lead (Pb(II)) and nickel (Ni(II)). For the concerned purpose 24 heavy metal resistant fungi are isolated from different industrial waste sites to form different microbial combinations as a single unit 'consortia' for achieving highest possible removal rates. Polymerase chain reaction and DNA sequencing are involved for the biochemical characterization and phylogenetic analysis of the screened isolates. The identification and screening studies reveal isolated strains as two Pb resistant fungi viz. K₁SF-Pb15 (Aspergillus terreus) and SEF-Pb (Talaromyces islandicus) which have shown metal removal up to 93% and two Ni(II) tolerant fungal isolates namely, MEF-Ni-11 (Neurospora crassa) and Ni-1 (Aspergillus flavus) with removal efficiency of more than 91%. Relationship has been validated between the biosorption capacity and efficiency of the novel consortium under the influence of variable pH, time duration, initial concentration of Pb(II) and Ni(II), and inoculum size which has led to the foundation of effective and economical parameters for its exploitation in practical fields. The fungal consortia when applied on various industrial effluents has exhibited more than 95% of removal for both Pb(II) and Ni(II) simultaneously. The detailed mechanistic insight has shown the involvement of physical, chemical and ionic forces for the removal of heavy metals. So the designed novel multi-biological combined system acted as a repository for Pb(II) and Ni(II) ions with a greater potential which can be guided by the mechanistic methodology for the retrieval and remediation of multiple heavy metals from the real waste water samples.

Amelioration of disulfonated Acid Red and hexavalent chromium phytotoxic effects on Triticum aestivum using bioremediating and plant growth-promoting Klebsiella pneumoniae SK1

Bacterial strain identified as Klebsiella pneumoniae SK1, based on 16S rDNA sequence study, was isolated from a textile mill discharge point at Dada Nagar industrial area in Kanpur, India in media containing 100 µg/ml each of disulfonated azo dye Acid Red 249 (AR) and hexavalent chromium [Cr(VI)]. SK1 is efficient in the concomitant decolorization and reduction of 100 µg/ml toxic AR and Cr(VI) respectively in 48 h under microaerophilic conditions. The efficacy of AR decolorization was found to be preeminent in static conditions, 37°C, 2-4% salinity and 7-9 pH range. 99% decolorization for initial AR concentration of 100 µg/ml in 48 h, and 91% for 250 µg/ml and 77% for 500 µg/ml was recorded in 72 h respectively in the presence of 100 µg/ml Cr(VI). Significant reductive changes in spectroscopic absorption spectra were observed for SK1 treated AR+Cr(VI) amended media with respect to controls. FITR spectroscopy was used to ascertain the breakage of the azo dye bond and the formation of biodegradative metabolites. Additionally, SK1 was found to be positive for indole acetic acid, ammonia, phosphate and potassium solubilization and biofilm formation. In plant bioassay, in vitro SK1 treated AR+Cr(VI) TSB media was used to treat Triticum aestivum in the soil environment. In comparison to untreated control, plants treated with bioremediation media shows increased percent germination, root and shoot length with a complete reversal of phytotoxic effects of the AR+Cr(VI) treated plants. In this study, environmental K. pneumoniae SK1 shows concomitant azo dye and Cr(VI) remediation with plant growth-promoting activity.

Performance and enhancement mechanism of corncob guiding chromium (VI) bioreduction

Chromium-contaminated groundwater has drawn extensive attention due to its high toxicity and wide application. Although bioremediation is considered to be an effective approach for Cr(VI) removal, a better method is still urgently needed. In this study, corncob-guided Cr(VI) reduction achieved the highest removal efficiency due to the highest amount of total carbon and available carbon emissions. After verifying the sustainability and operational feasibility of this approach, the broad-spectrum applicability of corncob to guide Cr(VI) bioreduction was further explored under various operating conditions. In addition, it suggested that the carrier effect, nutrient element release and electron shuttle effect were the main mechanisms enhancing the reduction process, with approximate contribution rates of 12.5%, 7.5% and 75%, respectively. Microbiological analysis demonstrated that the addition of solid-phase carbon sources increased the abundance of microbes related to carbon metabolism and promoted the expression of glycolytic metabolic pathway. Furthermore, the addition of corncob led to an elevation of expression level of the electron transport pathway, which is consistent with the function of the electron shuttle. This study provides theoretical and technical support for the practical application of corncob-mediated Cr(VI) bioreduction.

Machine Learning Modeling of Aerobic Biodegradation for Azo Dyes and Hexavalent Chromium

The present study emphasizes the efficacy of a biosurfactant-producing bacterial strain Klebsiella sp. KOD36 in biodegradation of azo dyes and hexavalent chromium individually and in a simultaneous system. The bacterial strain has exhibited a considerable potential for biodegradation of chromium and azo dyes in single and combination systems (maximum 97%, 94% in an individual and combined system, respectively). Simultaneous aerobic biodegradation of azo dyes and hexavalent chromium (SBAHC) was modeled using machine learning programming, which includes gene expression programming, random forest, support vector regression, and support vector regression-fruit fly optimization algorithm. The correlation coefficient includes the dispersion index, and the Willmott agreement index was employed as statistical metrics to assess the performance of each model separately. In addition, the Taylor diagram was used to further investigate the methods used. The findings of the present study were that the support vector regression-fruitfly optimization algorithm (SVR-FOA) with correlation coefficient (CC) of 0.644, (scattered index) SI of 0.374, and (Willmott’s index of agreement) WI of 0.607 performed better than the autonomous support vector regression (SVR), gene expression programming (GEP), and random forest (RF) methods. In addition, the standalone SVR model with CC of 0.146, SI of 0.473, and WI of 0.408 ranked the second best. In summary, the SBAHC can be accurately estimated using the hybrid SVR-FOA method. In other words, FOA has proven to be a powerful optimization algorithm for increasing the accuracy of the SVR method.

The improved methods of heavy metals removal by biosorbents: A review

For decades, a vast array of innovative biosorbents have been found out and used in the removal of heavy metals, including bacteria, algae and fungi, etc. Although extensive biological species have been tried as a biosorbent for heavy metals removal, for removal efficiency or economy efficiency limited, it has failed to make a substantial breakthrough in practical application. Thus, many improved methods based on biosorbents emerged. In this review, based on the literature and our research results, we highlight three types of novel methods for biosorbents removal of heavy metals: chemical modification of biosorbents; biomass and chemical materials combination; multiple biomass complex systems. We mainly focus on their configuration, biosorption performance, their creation method, regeneration/reuse, their application and development in the future. Through the comparative analysis of various methods, we think that intracellular autogenous nanomaterials may open up another window in biosorption of heavy metals area. At the same time, the combination of various treatment methods will be the development tendency of heavy metal pollution treatment in the future.

Microbial reduction fate of chromium (Cr) in aqueous solution by mixed bacterial consortium

Groundwater contaminated by Cr(VI) requires effective remediation to prevent adverse environmental impacts. The biodegradation of Cr(VI) has been documented for several decades, but little remains known about the removal fate of chromium, including the main species of reductase (sites) and functional genes involved in Cr(VI) reduction in mixed bacterial consortium. Cr(VI) reduction in this study was verified to be an enzyme-mediated process. Meanwhile, Cr(VI) reduction of different cell components demonstrated that the extracellular enzyme was the main active substance, and the distribution of Cr after experiment was quantified using mass balance calculation. Furthermore, the optimal pH for reduction was 8.0, with the reduction rate decreasing with increasing initial Cr(VI) concentrations. The co-existing oxyanions had little effect on Cr(VI) reduction, while the presence of other heavy metals had a relatively significant influence. The evolutionary behavior of microbial community structure and functional genes affected by Cr(VI) were also analyzed, which provided new insights on the underlying mechanisms involved in bioreduction in this study. These results generated new understanding of the reduction mechanisms on the Cr-relevant bacterial species and genes, which would be helpful in designing strategies for the bioremediation of Cr(VI) contaminated water.

Process optimization for effective bio-decolourization of reactive orange 16 using chemometric methods

Azo group containing reactive dyes are most commonly used in textile and tannery industries due to its bright appearance and stable color. This study aims to investigate the decolourization of reactive orange 16 (RO16) dye by Pseudomonas aeruginosa 23N1 along with removal of chromate (Cr(VI)) and evaluation of optimal process condition. The regular two-level factorial design is used to screen out operational parameters and selects their levels for further optimization process through central composite design (CCD) based response surface methodology (RSM). The result revealed that glucose and peptone have a negative effect on the performance of dye decolourization. Bacteria exhibit high decolourization potential in yeast extract supplemented culture medium with no addition of external carbon sources. The percentages of decolourization obtained in model validated experiments are obtained as 95.0 ± 0.4% and 95.1 ± 0.5% for initial dye 50 mg/L and 150 mg/L, respectively, which exhibit satisfactory correlation with model predicted response. The simultaneous dye and Cr(VI) removal has been explored in this study. The decolourization of dye is only affected due to presence of high Cr(VI) concentration (>120 mg/L). Bacteria have shown satisfactorily decolourization for RO16 contaminated industrial wastewater. The strain 23N1 could be a good biological agent for decolourization of RO16 dye.

The efficacy of bacterial species to decolourise reactive azo, anthroquinone and triphenylmethane dyes from wastewater: a review

The industrial dye-contaminated wastewater has been considered as the most complex and hazardous in terms of nature and composition of toxicants that can cause severe biotic risk. Reactive azo, anthroquinone and triphenylmethane dyes are mostly used in dyeing industries; thus, the unfixed hydrolysed molecules of these dyes are commonly found in wastewater. In this regard, bacterial species have been proved to be highly effective to treat wastewater containing reactive dyes and heavy metals. The bio-decolourisation of dye occurs either by adsorption or through degradation in bacterial metabolic pathways under optimised environmental conditions. The bacterial dye decolourisation rates vary with the type of bacteria, reactivity of dye and operational parameters such as temperature, pH, co-substrate, electron donor and dissolved oxygen concentration. The present paper reviews the efficiency of bacterial species (individual and consortia) to decolourise wastewater containing reactive azo, anthroquinone and triphenylmethane dyes either individually or mixed or with metal ions. It has been observed that bacteria Pseudomonas spp. are comparatively more effective to treat reactive dyes and metal-contaminated wastewater. In recent studies, either immobilised cell or isolated enzymes are being used to decolourise dye at a large scale of operations. However, it is required to investigate more potent bacterial species or consortia that could be used to treat wastewater containing mixed reactive dyes and heavy metals like chromium ions.

Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium

Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the wastewater contaminated with dyes and heavy metals.

A novel Pseudomonas gessardii strain LZ-E simultaneously degrades naphthalene and reduces hexavalent chromium

Combined pollutants with polycyclic aromatic hydrocarbons (PAHs) and heavy metals have been identified as toxic and unmanageable contaminates. In this work, Pseudomonas gessardii strain LZ-E isolated from wastewater discharge site of a petrochemical company degrades naphthalene and reduces Cr(VI) simultaneously. 95% of 10mgL(-1) Cr(VI) was reduced to Cr(III) while 77% of 800mgL(-1) naphthalene was degraded when strain LZ-E was incubated in BH medium for 48h. Furthermore, naphthalene promotes Cr(VI) reduction in strain LZ-E as catechol and phthalic acid produced in naphthalene degradation are able to reduce Cr(VI) abiotically. An aerated bioreactor system was setup to test strain LZ-E's remediation ability. Strain LZ-E continuously remediated naphthalene and Cr(VI) at rates of 15mgL(-1)h(-1) and 0.20mgL(-1)h(-1) of 800mgL(-1) naphthalene and 10mgL(-1) Cr(VI) addition with eight batches in 16days. In summary, strain LZ-E is a potential applicant for combined pollution remediation.

Biotreatment of simulated tannery wastewater containing Reactive Black 5, aniline and CrVI using a biochar packed bioreactor

Azo dyes and CrVI in tannery wastewater can be treated by redox active bacteria. Dye decolorization and CrVI reduction are simultaneous under anaerobic conditions. Biochar is an effective support matrix for packed bed bioreactors used to treat dyes and CrVI.

Isolation and characterization of Paracoccus sp. GSM2 capable of degrading textile azo dye Reactive Violet 5

A potential bacterial strain GSM2, capable of degrading an azo dye Reactive Violet 5 as a sole source of carbon, was isolated from textile mill effluent from Solapur, India. The 16S rDNA sequence and phenotypic characteristics indicated an isolated organism as Paracoccus sp. GSM2. This strain exhibited complete decolorization of Reactive Violet 5 (100 mg/L) within 16 h, while maximally it could decolorize 800 mg/L of dye within 38 h with 73% decolorization under static condition. For color removal, the most suitable pH and temperature were pH 6.0-9.0 and 25-40 °C, respectively. The isolate was able to decolorize more than 70% of five structurally different azo dyes within 38 h. The isolate is salt tolerant as it can bring out more than 90% decolorization up to a salt concentration of 2% (w/v). UV-Visible absorption spectra before and after decolorization suggested that decolorization was due to biodegradation and was further confirmed by FT-IR spectroscopy. Overall results indicate the effectiveness of the strain GSM2 explored for the treatment of textile industry effluents containing various azo dyes. To our knowledge, this could be the first report on biodegradation of Reactive Violet 5 by Paracoccus sp. GSM2.

Simultaneous decolorization of reactive Orange M2R dye and reduction of chromate by Lysinibacillus sp. KMK-A

Azo dyes constitute the largest and diverse group of dyes, widely used in number of industries that are contributing toward organic and inorganic load of effluent treatment. In the present study, Lysinibacillus sp. KMK-A was able to effectively decolorize Orange M2R dye up to 2000 mg l(-1) (Vmax of 19.6 mg l(-1) h(-1) and Km of 439 mg l(-1)) and reduce Cr(VI) up to 250 mg l(-1) (Vmax of 3.6 mg l(-1) h(-1) and Km 28.3 mg l(-1)). It also has an ability of simultaneous decolorization of Orange M2R dye (200-1000 mg l(-1)) with reduction of Cr(VI) (50-200 mg l(-1)). Significant reduction in total organic carbon content, chemical and biological oxygen demand along with spectroscopic and chromatographic analysis confirmed the biotransformation of Orange M2R. Involvement of enzymes namely azoreductase and chromate reductase was observed during biotransformation. The phyto and geno toxicity studies demonstrated that metabolites of dye degradation were non-toxic. Higher tolerance with simultaneous decolorization and detoxification of azo dyes in presence of Cr(VI) makes Lysinibacillus sp. KMK-A, a potential candidate for eco-friendly remediation of metal contaminated dye effluents.

Molecular fingerprinting of bacterial communities in enriched azo dye (Reactive Violet 5R) decolorising native acclimatised bacterial consortia

Reactive Violet 5R (RV5R) decolorising acclimatised bacterial consortia were enriched from industrial effluent contaminated and pristine samples from Gujarat, India on several different media. Twelve acclimatised consortia were selected for the study which were able to decolorise 100mg/L RV5R in 30 h under shaking or static conditions. Eubacterial diversity was studied by 16S rRNA gene based culture-independent methods, using HaeIII and Hinf1 enzymes for ARDRA and V3 region based DGGE analysis, forming total 6 clusters in both analysis. Decolorised end products of all the consortia were analysed by FTIR showing cleavage of the azo bond and group modifications. GC-MS data of dye decolorised end products of Gly consortium obtained from hydrocarbon contaminated soil demonstrated benzene ring cleavage activity. Present study suggests that enrichment of acclimatised consortia under different conditions can result in diverse microbial communities that differentially degrade RV5R and can provide rich source of dye decolorising strains.

A coupled biological and photocatalysis pretreatment system for the removal of crystal violet from wastewater

The efficiency of a coupled photocatalytic-biological system for removing crystal violet (CV) from an aqueous solution was assessed. Initial experiments demonstrated that the optimal operating parameters for the photoreactor were a 1.5-h reaction time, pH 7.0, and a 2.0-min retention time. Under these conditions, the photocatalytic reaction reduced the toxicity of the CV solution by 94%. Subsequent evaluation of the performance and characteristics of the coupled photocatalytic-biological system in terms of CV removal revealed that the coupled system successfully removed and efficiently mineralized CV in a semi-continuous mode when the CV concentration was <150mgL(-1). Based on our analysis of the degradation products, CV degradation in this coupled system involved stepwise demethylation and aromatic ring opening. Phylogenetic analysis of the bioreactor effluent showed that the predominant phyla were Proteobacteria, followed by Bacteroidetes and Actinobacteria, suggesting that this coupled system is conducive for such processes as demethylation, aromatic ring opening, carbon oxidation, and nitrification. These results were verified in a GC-MS analysis. To our knowledge, this is the first report on CV removal using a coupled system.

Decolorization and degradation of azo dye--Reactive Violet 5R by an acclimatized indigenous bacterial mixed cultures-SB4 isolated from anthropogenic dye contaminated soil

Azo dyes an important group of synthetic compounds are recalcitrant xenobiotics. Conventional technologies are unsuccessful to efficiently remove these compounds from contaminated environment. However, consorted metabolic functioning of innate microbial communities is a promising approach for bioremediation of polluted environment. Bacterial mixed cultures SB4 proficient in complete decolorization of azo dye - Reactive Violet 5R was developed through culture enrichment technique. Bacterial community composition based on 16S rRNA gene analysis revealed that mixed cultures SB4 composed of six bacterial strains namely Bacillus sp. V1DMK, Lysinibacillus sp. V3DMK, Bacillus sp. V5DMK, Bacillus sp. V7DMK, Ochrobacterium sp. V10DMK, Bacillus sp. V12DMK. SB4 grew well in minimal medium containing low amount of glucose and yeast extract (YE) (1 g/L) and decolorized 200mg/L of RV5 within 18 h under static condition. Mixed cultures SB4 decolorized wide range of azo dyes and maximum rate of decolorization was observed at 37 °C and pH 7.0. Decolorization efficiency was found to be unaltered under high RV5 and salt concentration where 1500 mg/L of RV5 was decolorized in presence of 20 g/L NaCl. We propose the asymmetric cleavage of RV5 and Fourier transformed infrared (FTIR), NMR and gas chromatography-mass spectrometry (GC-MS) confirmed the formation of four intermediatory compounds 1-diazo-2-naphthol, 4-hydroxybenzenesulphonic acid, 2-naphthol and benzenesulphonic acid.

Advances in molecular and "-omics" technologies to gauge microbial communities and bioremediation at xenobiotic/anthropogen contaminated sites

Microbial bioremediation has been well-demonstrated as an ecofriendly and cost-competitive strategy for elimination of xenobiotic and or anthropogenic compounds from the polluted environments. However, successful execution of these versatile bioremediation strategies requires a thorough understanding of factors governing the growth, metabolism, dynamics and functions of indigenous microbial communities at contaminated sites. Recent innovative breakthroughs in genotypic profiling, ultrafast genome pyrosequencing, metagenomics, metatranscriptomics, metaproteomics and metabolomics along with bioinformatics tools have provided crucial in-sights of microbial communities and their mechanisms in bioremediation of environmental pollutants. Moreover, advances in these technologies have significantly improved the process of efficacy determination and implementation of microbial bioremediation strategies. The current review is focused on application of these molecular and "-omics" technologies in gauging the innate microbial community structures, dynamics and functions at contaminated sites or pollution containment facilities.