Chemistry in the Molten State: Opportunities for Designing and Tuning the Emission Properties of Halide Perovskites.

A series of monolayered lead halide hybrid perovskites (HO2C(CH2)n-1NH3)2PbX4, named (Cn)2PbX4 (n = 4-6, X = Cl, Br), exhibiting a low congruent melting temperature (Tm) (Tm = 130 °C for (C4)2PbBr4), high stability in the molten state, and whitish type emission, are reported. From the synthesis in the molten state, rare solid solutions of mixed organic cations (Cn1-xCn'x)2PbX4 (n, n' = 4-6; X = Cl, Br; 0 ≤ x ≤1) as well as solid solutions of mixed halides (Cn)2Pb(X1-yX'y)4 (n = 4-6; X, X' = Cl, Br; 0 ≤ y ≤1) have been prepared and characterized (thermal behavior, powder X-ray diffraction (PXRD), photoluminescence properties). The impact of substitutions is significant on the thermal properties, lowering the Tm down to 100 °C for (C4)2Pb(Br0.25Cl0.75)4. The emission properties are slightly tuned in the case of mixed organic cation systems, whereas modifications are more dramatic in the case of mixed halide systems, leading to emission properties through the entire visible region. These results illustrate the great opportunities offered by the congruent melting properties of halide perovskites allowing syntheses in the molten state.

Recycling of gas-to-liquid sludge as a potential organic amendment: Effect on soil and cotton properties under hyperarid conditions.

Gas-to-liquid (GTL) sludge is a specific wastewater treatment by-product, which is generated during the industrial process of natural gas conversion to transportation fuels. This least studied sludge is pathogen-free and rich in organic carbon and plant nutrients. Therefore, it can be reused for soil enhancement as a sustainable management strategy to mitigate landfill gas emissions. In this field study, we compared the performance of soil treatments with GTL sludge to the more conventional chemical fertilizers and cow manure compost for the cultivation of cotton under hyperarid conditions. After a complete growing season, GTL sludge application resulted in the enhancement of soil properties and plant growth compared to conventional inputs. As such, there was a significant dose-dependent increase of soil organic matter (4.01% and 4.54%), phosphorus (534 and 1090 mg kg-1), and cumulative lint yield (4.68 and 5.67 t ha-1) for GTL sludge application rates of 1.5% and 3%, respectively. The produced fiber quality was adequate for an upland cotton variety (Gossypium hirsutum var. MAY 344) and appeared more dependent on the prevailing climate conditions than soil treatments. On the other hand, the adverse effects generally related to industrial sludge reuse were not significant and did not affect the designed agro-environmental system. Accordingly, plants grown on GTL sludge-amended soils showed lower antioxidant activity despite significant salinity increase. In addition, the concentrations of detected heavy metals in soil were within the standards' limits, which did not pose environmental issues under the described experimental conditions. Leachate analysis revealed no risks for groundwater contamination with phytotoxic metals, which were mostly retained by the soil matrix. Therefore, recycling GTL sludge as an organic amendment can be a sustainable solution to improve soil quality and lower carbon footprint. To reduce any environmental concerns, an application rate of 1.5% could be provisionally recommended since a two-fold increase in sludge dose did not result in a significant yield improvement.

Adsorptive batch and biological treatments of produced water: Recent progresses, challenges, and potentials.

Produced water is responsible for the largest contribution in terms of waste stream volume associated with the production of oil and gas. Characterization of produced water is very crucial for the determination of its main components and constituents for optimal selection of the treatment method. This review aims to review and critically discuss various treatment options that can be considered cost-efficient and environmentally friendly for the removal of different pollutants from produced water. Great efforts and progresses were made in various treatment options, including batch adsorption processes, membrane filtration, advanced oxidation, biological systems, adsorption, coagulation, and combined processes. Chemical precipitation, membrane filtration, and adsorption have high removal efficiencies that can reach more than 90% for different produced water components. The most effective method among these methods is adsorption using different adsorbents media. In this review, date-pits activated carbons, microemulsions-modified date pits, and cellulose nanocrystals as low-cost adsorbents were thoroughly reviewed and discussed. Moreover, the potential of using biological treatments in the removal of various pollutants from produced water such as conventional activated sludge, sequential batch reactor, and fixed-film biological aerated filter reactors were systematically discussed. Generally, produced water can be utilized in various fields including habitat and wildlife, agricultural and irrigation sector, energy sector, fire control, industrial use also power regeneration. The degree of treatment will depend on the application that produced water is being reused in. For instance, to use produced water in oil and gas industries, water will require minimal treatment while for agricultural and drinking purposes high treatment level will be required. It can also be concluded that one specific technique cannot be recommended that will meet all requirements including environmental, reuse, and recycling for sustainable energy. This is because of various dominant factors including the type of field, platform type, chemical composition, geological location, and chemical composition of the production chemicals.

An overview of brine management: Emerging desalination technologies, life cycle assessment, and metal recovery methodologies.

This study examines which management methods are the most recent and advanced in managing rejected brine generated from desalination plants. It also provides up-to-date information regarding the most adequate technologies that generate a minimum quantity of rejected brine via the use of minimization techniques and analyzes the method of direct disposal that has lately received noticeable improvements. It further discusses the reuse of discarded brine to recover valuable goods and sequestration of carbon dioxide. Sustainability is an important parameter that needs consideration to achieve uninterrupted operation of the discarded brine management to achieve the least environmental, social, and economic aftermath. To properly deal with any environmental issues related to brine disposal, different methods are implemented so that, in the end, higher water recovery is achievable from the desalination processes, namely brine minimization and rejection technologies (pressure retarded osmosis, microbial desalination cell technology), membrane-based technologies (vibratory shear enhanced processing, forward osmosis, electrodialysis, electrodialysis reverse, and electrodialysis metathesis, pervaporation method, thermal-based technologies (wind-aided intensified evaporation, brine concentrators, ohmic evaporator, membrane distillation, multi-stage flash distillation. This review also critically examined the two conventional approaches commonly used in life cycle assessment (LCA), when evaluating the ecotoxic effect of discarded brine. It intends to discuss the currently available methods and propose an improved method for evaluating the toxicity potential of brine on the aquatic ecosystem originated from seawater desalination plants. The Group-by-Group method takes into consideration the demerits of the two methods of the traditional method of LCA or chemical-specific approach as it provides a more holistic coverage for complicated brine to be disposed of. Recently, attention has been focused on recovering valuable metals from the discharged concentrated brine waste. Certainly, attaining marketable products from the discharged concentrated brine would offer an economic benefit and reducing the whole desalination costs. Ion imprinting polymers have potential applications in metal recovery from brine. Finding selective, more efficient, and less expensive imprinted polymers for extraction/pre-concentration of valuable ions is a vital and challenging task. Lastly, the brine should be seen as a resource and not as a waste to attain sustainability in its management approaches. Hybrid processes would be highly recommended to get the absolute transformation of the discarded brine from desalination processes to more valuable constituents.

The Key Role of the Interface in the Highly Sensitive Mechanochromic Luminescence Properties of Hybrid Perovskites.

Hybrid perovskite (HP) materials are of interest in photovoltaics and lighting applications. Here we report that hybrid perovskite composites, as crystallized powders, can behave as intelligent materials showing highly sensitive and reversible mechanochromic luminescence (MCL). Composites consisting of monolayered 2D HP and 3D HP components exhibit reversible tunable color emission upon mechanical strain. The bluish-whitish emission of the 2D HP turns into orange in the composite owing to an energy transfer process. The bright green emission, observed as soon as the composite is slightly crushed, originates from the 3D HP after efficient energy funneling from the multi-layered 2D HP produced at the 2D/3D interface by the mechanical treatment. Besides highlighting the key role of the interfaces in light emission of HP, our findings pave the way for hybrid perovskites as highly sensitive MCL smart materials for mechanosensors, security papers, or optical storage applications.

Microbially induced calcite precipitation in calcareous soils by endogenous Bacillus cereus, at high pH and harsh weather.

Microbially induced calcite precipitation (MICP) improves the physical properties of soils by increasing the solid content, decreasing the pore sizes and improving the rigidity of the particle-to-particle contact ending with a better mechanical and geotechnical performances of the soils. First, the physical characteristics of soils in Qatar showed similar grain size distributions with most falling in the category of fine particles (30 µm-1 µm), which is appropriate for MICP processes. MICP is ensured by the ureolytic activity of urease producing bacteria. However, Qatari soils are characterized with high carbonate contents exceeding 20%, high alkalinity and fluctuations of temperature and aeration. Although such properties can cause calcite dissolution as reported in literature, two Qatari endogenous B. cereus strains, QBB4 and QBB5, were shown able to adapt to the harsh conditions and induce mineral formations by MICP. Their optimal potentials was at wide ranges of temperature from 30 °C to 42 °C and pH from 7.0 to 8.0. Using Qatari bacteria in liquid cultures and at syringe level at laboratory conditions, as well as in plots at field conditions, 16% CaCO3 increase in minerals formation was obtained, leading to 7% increase of soils stability. Increase of carbonate contents was also shown by an increase in the stability of aggregates to disintegration when incubated in water using a 0.25 mm sieve. MICP in Qatari soils is feasible using B. cereus QBB4, as this is an endogenous bacterium that tolerates harsh conditions, high alkalinity and calcium contents. The performance of these bacterial strains was achieved with clear formation of aragonite, feldspars and quartz in the calcareous soils.

Evaluating the effect of antiscalants on membrane biofouling using FTIR and multivariate analysis.

A combination of Fourier-transform infrared (FTIR) spectroscopy, multivariate analysis and conventional microbiological assays were utilized to characterize and differentiate membrane biofouling formed in the presence of antiscalants. Based on the FTIR spectra of biofouled reverse osmosis membranes obtained after incubating with antiscalants and H. aquamarina (as model microorganism), it was found that the biofouling intensity and composition was dependent on the type of antiscalants used. The growth of the bacterium was also highly affected by the type of antiscalants as shown by the colony forming unit (CFU) counts. By combining the techniques of principle component analysis (PCA) and FTIR, it was demonstrated that the biofouling was more intense and composed of proteins, polysaccharides and lipids, when polymer antiscalant was used. By applying PCA-FTIR with CFU counts, faster prediction of the effect of antiscalants on biofouling was made possible.

Identification and overcome of limitations of weathered oil hydrocarbons bioremediation by an adapted Bacillus sorensis strain.

Because of the high production of oil and gas in Qatar, the likelihood of oil spill occurrence is most probably susceptible to happen. Contaminated soil treatment is very expensive. Cost effective mechanisms are investigated to treat this threatening issue. For that reason, bioremediation and biotechnology tools are introduced to help accelerate and remove the pollution caused by the contamination process. This paper demonstrated the importance of optimising the treatment conditions to the indigenous bacterial strain to obtain the highest biodegradation efficiency rates. The usage of biopile system technology was used with biostimulation and bioaugmentation processes. The indigenous Bacillus sonorensis (B. sonorensis) D1 bacterium played a crucial role in the biodegradation process when introduced to optimized conditions; carbon/nitrogen/phosphorus (C/N/P) (100/10/1), temperature (37 °C), surfactant tween 80 (0.12% (v/w)), and moisture (10%). Gas chromatography (mass spectrometry/flame ionization detector) (GC- (MS/FID)), Fourier transform infrared (FTIR), and colony-forming unit (CFU) analyses were performed. The diesel range organics (DRO) and polycyclic aromatic hydrocarbons (PAH) removal (%) of the weathered oil contaminated soil reached, after 160 days, 39.2% and 32.4% simultaneously when ammonium nitrate was used as a nitrogen source. Whereas urea inhibited the oil degradation process and caused the pH to rise to 9.55.

Ectopic Expression of Aeluropus littoralis Plasma Membrane Protein Gene AlTMP1 Confers Abiotic Stress Tolerance in Transgenic Tobacco by Improving Water Status and Cation Homeostasis.

We report here the isolation and functional analysis of AlTMP1 gene encoding a member of the PMP3 protein family. In Aeluropus littoralis, AlTMP1 is highly induced by abscisic acid (ABA), cold, salt, and osmotic stresses. Transgenic tobacco expressing AlTMP1 exhibited enhanced tolerance to salt, osmotic, H2O2, heat and freezing stresses at the seedling stage. Under greenhouse conditions, the transgenic plants showed a higher level of tolerance to drought than to salinity. Noteworthy, AlTMP1 plants yielded two- and five-fold more seeds than non-transgenic plants (NT) under salt and drought stresses, respectively. The leaves of AlTMP1 plants accumulated lower Na⁺ but higher K⁺ and Ca2+ than those of NT plants. Tolerance to osmotic and salt stresses was associated with higher membrane stability, low electrolyte leakage, and improved water status. Finally, accumulation of AlTMP1 in tobacco altered the regulation of some stress-related genes in either a positive (NHX1, CAT1, APX1, and DREB1A) or negative (HKT1 and KT1) manner that could be related to the observed tolerance. These results suggest that AlTMP1 confers stress tolerance in tobacco through maintenance of ion homeostasis, increased membrane integrity, and water status. The observed tolerance may be due to a direct or indirect effect of AlTMP1 on the expression of stress-related genes which could stimulate an adaptive potential not present in NT plants.

Flavonoid profile and antioxidant activities of methanolic extract of Hyparrhenia hirta (L.) Stapf.

In this study, we report isolation of flavonoids, viz., 3-O-methylquercetin, tangeritin, luteolin-7-O-glucoside, luteolin, apigenin-7-O-glucoside, apigenin-8-C-glucoside, luteolin-8-C-glucoside, luteolin-6-C-glucoside, diosmetin and catechin from the methanolic extract of Hyparrhenia hirta employing high performance liquid chromatography and liquid chromatography-electrospray ionization-tandem mass spectrometry. The total phenolic content of H. hirta extract was 105.58 ± 0.1 mg gallic acid equivalents/g of plant extract while the total flavonoid content was 45.20 ± 0.2 mg quercetin equivalents/g of plant extract and the total condensed tannin were 72.35 ± 0.7 mg catechin equivalents/g of plant extract by reference to standard curve. The antioxidant activity was assayed through the antioxidant capacity by phosphomolybdenum assay, the reducing power assay and the radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl method. The extract showed dose dependant activity in all the three assays.

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination.

The synthesis and full characterization of two tetrathiafulvalene-appended azine ligands, namely 2-([2,2'-bi(1,3-dithiolylidene)]-4-yl)-6-((2,4-dinitrophenyl)hydrazono)methyl)pyridine (L1) and 5-([2,2'-bi(1,3-dithiolylidene)]-4-yl)-2-((2,4-dinitrophenyl)hydrazono)methyl)pyridine (L2) are described. The crystal structure of ligand L1 indicates that the ligand is completely planar with the presence of a strong intramolecular N3-H3···O1 hydrogen bonding. Titration experiments with inorganic anions showed that both ligands are suitable candidates for the sensing of fluoride anions. Ligand L2 was reacted with a Re(I) cation to yield the corresponding rhenium tricarbonyl complex 3. In the crystal structure of the newly prepared electroactive rhenium complex the TTF is neutral and the rhenium cation is hexacoordinated. The electrochemical behavior of the three compounds indicates that they are promising for the construction of crystalline radical cation salts.

Diversity of hydrocarbon-degrading bacteria in mangroves rhizosphere as an indicator of oil-pollution bioremediation in mangrove forests.

Mangrove ecosystems, characterized by high levels of productivity, are susceptible to anthropogenic activities, notably oil pollution arising from diverse origins including spills, transportation, and industrial effluents. Owing to their role in climate regulation and economic significance, there is a growing interest in developing mangrove conservation strategies. In the Arabian Gulf, mangroves stand as the sole naturally occurring green vegetation due to the region's hot and arid climate. However, they have faced persistent oil pollution for decades. This review focuses on global mangrove distribution, with a specific emphasis on Qatar's mangroves. It highlights the ongoing challenges faced by mangroves, particularly in relation to the oil industry, and the impact of oil pollution on these vital ecosystems. It outlines major oil spill incidents worldwide and the diverse hydrocarbon-degrading bacterial communities within polluted areas, elucidating their potential for bioremediation. The use of symbiotic interactions between mangrove plants and bacteria offers a more sustainable, cost-effective and environmentally friendly alternative. However, the success of these bioremediation strategies depends on a deep understanding of the dynamics of bacterial communities, environmental factors and specific nature of the pollutants.

Insights into population adaptation and biodiversity of lactic acid bacteria in challenged date palm leaves silaging, using MALDI-TOF MS.

The study focused on isolating indigenous Qatari lactic acid bacteria (LAB) from various challenged date palm tree leaf silages to construct a comprehensive strain collection, useful to study the diversity of these strains following their adaptation to the uncommon silage. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) was employed for strain identification and differentiation. The diversity of LAB populations and strains was assessed through principal component analysis (PCA) and dendrogram analyses. A total of 88 LAB isolates were obtained from silages of fresh palm leaves, silage of mixed leaves and dairy feed, along with fresh palm tree leaves, and dairy feed, adapted to local harsh environments. These isolates were categorized according to the new classification of 2020, belonging to genera of Pediococcus, Lactiplantibacillus plantarum, Lacticaseibacillus paracasei, Companilactobacillus farciminis, Limosilactobacillus oris, Limosilactobacillus vaginalis, Lactiplantibacillus pentosus and Lactobacillus johnsonii. Pediococcus was the most prevalent genus, falling mostly within the species Pediococcus lolii. MALDI-TOF MS protein profiles, PCA, and dendrogram analyses successfully grouped the LAB isolates into five distinctive clusters based on the protein's similarities. The high diversity of the indigenous LAB in spontaneous palm leaf silages demonstrated their adaptation and mutualistic interactions, forming robust consortia that ensure the quality of the silage. The straightforward, quick, and accurate identification of LAB in this silage using MALDI-TOF MS presents a valuable approach for formulating LAB consortia for silaging harsh agricultural by-products.

Optimization of bioinsecticides overproduction by Bacillus thuringiensis subsp. kurstaki using linear regression.

A multiple linear regression analyses were performed to screen for the significant factors simultaneously influencing production of deltaendotoxin, proteolytic activities and spore formation by a Bacillus thuringiensis kurstaki strain. Investigated factors included: pH of the medium, available oxygen and inoculum size. It was observed that oxygen availability was the most influencing setting on both deltaendotoxins production and spores counts, followed by initial pH of the medium and inoculum size. On other hand, pH of medium was found to be the most significant parameter for proteolytic activity, followed by inoculum size and dissolved oxygen. Our results suggested that the first order with two-factor interaction model seemed to be more satisfactory than simple first order model for optimization of delta-endotoxin overproduction. The coefficients of determination (R') indicated a better adequacy of the second order models to justify the obtained data. Based on results, relationships between delta-endotoxins production, proteolytic activities and spores counts were established. Our results can help to balance delta-endotoxins production and its stability.

Study of diversity of mineral-forming bacteria in sabkha mats and sediments of mangrove forest in Qatar.

The involvement of microorganisms in carbonate minerals and modern dolomite formation in evaporitic environments occupied with microbial mats (i.e., sabkha) and in mangrove forests is evidenced, while its potential diversity requires further elucidation. Microorganisms can create supersaturated microenvironments facilitating the formation of various carbonate minerals through specific metabolic pathways. This is particularly important in arid environments, where deposition and sedimentary structures can occur. This study investigated the biodiversity of halophilic, heterotrophic, and aerobic mineral-forming bacteria in mangrove forests and living and decaying mats of Qatari sabkha. The diversity study was performed at the protein level using MALDI-TOF mass spectrometry protein profiles combined with principal component analysis (PCA), which revealed a high diversity of isolated strains at the taxonomy and protein profile levels. The diversity of the minerals formed in pure cultures was evidenced by SEM/EDS and XRD analysis. Different types of carbonate minerals (calcium carbonate, magnesium carbonates, and high-magnesium calcites) were formed in pure cultures of the studied strains, which might explain their occurrence in the bulk composition of the sediments from where the strains were isolated. These results illuminate the diversity of biological mineral-formation processes in the extreme environments of Qatari sabkhas and mangroves, explaining the high diversity of minerals in these environments.

Improvement of Photorhabdus temperata strain K122 bioinsecticide production by batch and fed-batch fermentations optimization.

Optimization of a fermentation process for bioinsecticides production by Photorhabdus temperata strain K122 was investigated into fully controlled 3-L fermenter using an optimized medium (OM). Development of large-scale inocula showed that the composition of the growth medium greatly influenced the physiological state of P. temperata cells. The effect of pH, agitation and dissolved oxygen concentration (DO) on the growth, culturability and oral toxicity of P. temperata cells were also investigated. Indeed, maintaining the pH at 7 and controlling DO concentration at 50 % saturation throughout the fermentation process, improved biomass production, CFU counts and oral toxicity by 41.1, 35 and 32.1 %, respectively, as compared to cultures carried out in 500 mL shake flasks. At such conditions, 8 g/L glucose fed-batch fermentation, enhanced cell lysis and variants small colony (Vsm) polymorphism appearance. To overcome such limitations, glucose concentration should be maintained at 4 g/L. In this case, P. temperata cells were produced at high cell density and culturability reaching 4.5 and 1.2 × 10(9) cells/mL, respectively. In addition, the stability of the primary form was maintained for a long period in the stationary growth phase and Vsm polymorphism was completely avoided that can be crucial for scale-up the bioprocess of P. temperata bioinsecticide.

Medium optimization of antifungal activity production by Bacillus amyloliquefaciens using statistical experimental design.

In order to overproduce biofungicides agents by Bacillus amyloliquefaciens BLB371, a suitable culture medium was optimized using response surface methodology. Plackett-Burman design and central composite design were employed for experimental design and analysis of the results. Peptone, sucrose, and yeast extract were found to significantly influence antifungal activity production and their optimal concentrations were, respectively, 20 g/L, 25 g/L, and 4.5 g/L. The corresponding biofungicide production was 250 AU/mL, corresponding to 56% improvement in antifungal components production over a previously used medium (160 AU/mL). Moreover, our results indicated that a deficiency of the minerals CuSO(4), FeCl(3) · 6H(2)O, Na(2)MoO(4), KI, ZnSO(4) · 7H(2)O, H(3)BO(3), and C(6)H(8)O(7) in the optimized culture medium was not crucial for biofungicides production by Bacillus amyloliquefaciens BLB371, which is interesting from a practical point of view, particularly for low-cost production and use of the biofungicide for the control of agricultural fungal pests.

Correlation between synthesis variation of 2-alkylquinolones and the antifungal activity of a Burkholderia cepacia strain collection.

Twenty epiphytic and rhizospheric bacterial strains harbouring strong antifungal activities were isolated from the Tunisian environment. This group of bacteria was identified as Burkholderia cepacia genomovar I using 16S rDNA and recA fragment gene sequence analyses for two selected strains and RFLP technique for the eighteen other ones. This identification did not show variability between isolates despite the significant differences in the antifungal activities of their culture supernatant and the organic crude extract against Aspergillus niger and other phytopathogenic fungi. Chromatographic and mass spectrometric analyses of these extracts allowed us to confirm the difference between strains of the group. Their metabolic production showed differences in term of contents and quantities of secreted molecules, particularly those which were identified to be involved in the antifungal activities. Two metabolites, named Bc-255 and Bc-257 secreted by the entire group at different amounts, have been purified and tested separately against A. niger. Bc-255 showed an activity twice as high as those shown by Bc-257. The structural characterization of these two compounds by mass spectrometry and nuclear magnetic resonance spectroscopy allowed their identification as two analogous 2-alkylquinolones with only one difference at the alkyl chain.

Immobilization of heavy metals by microbially induced carbonate precipitation using hydrocarbon-degrading ureolytic bacteria.

Crude oil contamination introduces multiple threats to human health and the environment, most of which are from toxic heavy metals. Heavy metals cause significant threats because of their persistence, toxicity, and bio-accumulation. Biomineralization, performed through many microbial processes, can lead to the immobilization of heavy metals in formed minerals. The potential of the microbially carbonate-induced precipitation (MICP) in removal by biomineralization of several heavy metals was investigated. A collection of diverse 11 bacterial strains exhibited ureolytic activity and tolerance to heavy metals when growing in Luria-Bertani (LB) and urea medium. Determination of the minimum inhibitory concentrations (MIC) revealed that heavy metal toxicity was arranged as Cd > Ni > Cr > Cu > Zn. Three hydrocarbon-degrading bacterial strains (two of Pseudomonas aeruginosa and one of Providencia rettgeri) exhibited the highest tolerance (MIC > 5 mM) to Cu, Cr, Zn, and Ni, whereas Cd exerted significantly higher toxicity with MIC <1 mM. At all MICP conditions, different proportions of calcium carbonate (calcite) and calcium phosphate (brushite) were formed. Pseudomonas aeruginosa strains (QZ5 and QZ9) exhibited the highest removal efficiency of Cr (100%), whereas Providencia rettgeri strain (QZ2) showed 100% removal of Zn. Heavy metal complexes were found as well. Cd removal was evidenced by the formation of cadmium phosphate induced by Providencia rettgeri bacterial activity. Our study confirmed that hydrocarbon-degrading ureolytic bacteria not only can tolerate heavy metal toxicity but also have the capability to co-precipitate heavy metals. These findings indicate an effective and novel biological approach to bioremediate petroleum hydrocarbons and immobilize multiple heavy metals with mineral formation. This is of high importance for ecological restoration via stabilization of soil and alleviation of heavy metal toxicity.

Proteomic analysis of T. qataranse exposed to lead (Pb) stress reveal new proteins with potential roles in Pb tolerance and detoxification mechanism.

Soil lead (Pb) contamination is one of the environmental problems facing the modern world. Sources of Pb in soil include industrial activities such as mining and smelting processes, agricultural activities such as application of insecticide and municipal sewage sludges, and urban activities such as use of lead in gasoline, paints, and other materials. Phytoremediation is the direct use of living green plants and is an effective, cheap, non-invasive, and environmentally friendly technique used to transfer or stabilize all the toxic metals and environmental pollutants in polluted soil or groundwater. Current work in this area is invested in elucidating mechanisms that underpin toxic-metal tolerance and detoxification mechanisms. The present study aims to gain insight into the mechanisms of Pb tolerance in T. qataranse by comparative proteomics. MALDI-TOF/MS and in silico proteome analysis showed differential protein expression between treated (50 mg kg⎯1 Pb) and untreated (0 mg kg⎯1 Pb) T. qataranse. A total of eighty-six (86) differentially expressed proteins, most of which function in ion and protein binding, antioxidant activity, transport, and abiotic response stress, were identified. In addition, essential stress-regulating metabolic pathways, including glutathione metabolism, cellular response to stress, and regulation of HSF1-mediated heat shock response, were also enriched. Also, at 52- and 49-kDa MW band areas, up to six hypothetical proteins with unknown functions were identified. Of these, protein AXX17_AT2G26660 is highly rich in glycine amino acid residues (up to 76%), suggesting that it is a probable glycine-rich protein (GRP) member. Although GRPs are known to be involved in plant defense against abiotic stress, including salinity and drought, there is no report on their role on Pb tolerance and or detoxification in plants. Further enrichment analysis in the current study reveals that the hypothetical proteins do not interact with known proteins and are not part of any enriched pathway. However, additional research is needed to functionally validate the role of the identified proteins in Pb detoxification mechanism.