Effect of the acclimation of a Streptomyces consortium on lindane biodegradation by free and immobilized cells

Exploring the potential of Meyerozyma caribbica and its combined application with bacteria for lindane bioremediation

This study explored the degradation potential of a yeast strain, Meyerozyma caribbica, alone and in combination with Bacillus velezensis and Priestia megaterium, found novel for lindane biodegradation. Isolated from hexachlorocyclohexane (HCH)-contaminated sites, M. caribbica, B. velezensis, and P. megaterium demonstrated lindane reduction efficiencies of 86.5%, 78.6%, and 77.5%, respectively, at 750 mg L⁻1 within 10-day incubation period. Kinetic analysis revealed that M. caribbica followed the first-order degradation (r2 = 0.991; T₁/₂ = 4.3 days). Notably, M. caribbica exhibited the highest dechlorinase activity (9.27 U mL⁻1) in the cell supernatant. Co-cultivation as the mixed culture of M. caribbica and P. megaterium achieved maximum lindane reduction (90%) and dechlorinase activity (9.93 U mL⁻1). Whereas the mixed culture of M. caribbica and B. velezensis resulted in 80.9% reduction at 500 mg L⁻1 lindane with dechlorinase activity of 6.77 U mL⁻1. Growth kinetics, modelled using the Monod equation, showed a maximum specific growth rate of 0.416 h⁻1 for the mixed culture of M. caribbica and P. megaterium at 750 mg L⁻1 lindane. GC-MS analysis confirmed the presence of intermediate metabolites, viz., γ-pentachlorocyclohexane, 1,2,4-trichlorobenzene, 1,4-dichlorobenzene and maleyl acetate, validated successive dechlorination and oxidative-reduction processes during lindane biodegradation. The findings of the study highlighted the potential of these novel microbial strains and their mixed cultures for effective bioremediation of lindane-contamination.

Potential and prospects of Actinobacteria in the bioremediation of environmental pollutants: Cellular mechanisms and genetic regulations

Increasing industrialization and anthropogenic activities have resulted in the release of a wide variety of pollutants into the environment including pesticides, polycyclic aromatic hydrocarbons (PAHs), and heavy metals. These pollutants pose a serious threat to human health as well as to the ecosystem. Thus, the removal of these compounds from the environment is highly important. Mitigation of the environmental pollution caused by these pollutants via bioremediation has become a promising approach nowadays. Actinobacteria are a group of eubacteria mostly known for their ability to produce secondary metabolites. The morphological features such as spore formation, filamentous growth, higher surface area to volume ratio, and cellular mechanisms like EPS secretion, and siderophore production in Actinobacteria render higher resistance and biodegradation ability. In addition, these bacteria possess several oxidoreductase systems (oxyR, catR, furA, etc.) which help in bioremediation. Actinobacteria genera including Arthrobacter, Rhodococcus, Streptomyces, Nocardia, Microbacterium, etc. have shown great potential for the bioremediation of various pollutants. In this review, the bioremediation ability of these bacteria has been discussed in detail. The utilization of various genera of Actinobacteria for the biodegradation of organic pollutants, including pesticides and PAHs, and inorganic pollutants like heavy metals has been described. In addition, the cellular mechanisms in these microbes which help to withstand oxidative stress have been discussed. Finally, this review explores the Actinobacteria mediated strategies and recent technologies such as the utilization of mixed cultures, cell immobilization, plant-microbe interaction, utilization of biosurfactants and nanoparticles, etc., to enhance the bioremediation of various environmental pollutants.

Applied of actinobacteria consortia-based bioremediation to restore co-contaminated systems

Global industrialization and natural resources extraction have left cocktails of environmental pollutants. Thus, this work focuses on developing a defined actinobacteria consortium able to restore systems co-contaminated with pollutants occurring in Argentinian environments. In this context, five actinobacteria were tested in solid medium to evaluate antagonistic interactions and tolerance against lindane (LIN), Reactive Black B-V (RBV), phenanthrene (Ph) and Cr(VI). The strains showed absence of antagonism, and most of them tolerated the presence of individual pollutants and their mixtures, except Micromonospora sp. A10. Thus, a quadruple consortium constituted by Streptomyces sp. A5, M7, MC1, and Amycolatopsis tucumanensis DSM 45259^T, was tested in liquid systems with individual contaminants. The best microbial growth was observed in the presence of RBV and the lowest on Cr(VI). Removals detected were 83.3%, 65.0% and 52.4% for Ph, RBV and LIN, respectively, with absence of Cr(VI) dissipation. Consequently, the consortium performance was tested against the organic mixture, and a microbial growth similar to the biotic control and a LIN removal increase (61.2%) were observed. Moreover, the four actinobacteria of the consortium survived the mixture bioremediation process. These results demonstrate the potential of the defined actinobacteria consortium as a tool to restore environments co-contaminated with organic pollutants.

Actinobacteria bioaugmentation and substrate evaluation for biobeds useful for the treatment of atrazine residues in agricultural fields

Biopurification systems (BPS) or biobeds are bioprophylaxis systems to prevent pesticide point-source contamination, whose efficiency relies mostly on the pesticide removal capacity of the biomixture, the majority component of a BPS. The adaptation of the components of the biomixtures to local availabilities is a key aspect to ensure the sustainability of the system. In this work, the removal of atrazine (ATZ) was evaluated in biomixtures formulated with three sugarcane by-products as alternative lignocellulosic substrates. Based on the capacity of actinobacteria to tolerate and degrade diverse pesticides, the effect of biomixtures bioaugmentation with actinobacteria was evaluated as a strategy to enhance the depuration capacity of biobeds. Also, the effect of ATZ and/or the bioaugmentation on microbial developments and enzymatic activities were studied. The biomixtures formulated with bagasse, filter cake, or harvest residue, reached pesticide removal values of 37-41% at 28 d of incubation, with t_1/2 between 37.9 ± 0.4 d and 52.3 ± 0.4 d. The bioaugmentation with Streptomyces sp. M7 accelerated the dissipation of the pesticide in the biomixtures, reducing ATZ t_1/2 3-fold regarding the controls, and achieving up to 72% of ATZ removal. Atrazine did not exert a clear effect on microbial developments, although most of the microbial counts were less in the contaminated biomixtures at the end of the assay. The bioaugmentation improved the development of the microbiota in general, specially actinobacteria and fungi, regarding the non-bioaugmented systems. The inoculation with Streptomyces sp. M7 enhanced acid phosphatase activity and/or reversed a possible effect of the pesticide over this enzymatic activity.

Lindane removal in contaminated soil by defined microbial consortia and evaluation of its effectiveness by bioassays and cytotoxicity studies

Lindane contamination in different environmental matrices has been a global concern for long. Bacterial consortia consisting of Paracoccus sp. NITDBR1, Rhodococcus rhodochrous NITDBS9, Ochrobactrum sp. NITDBR3, NITDBR4 and NITDBR5 were used for the bioremediation of soil artificially contaminated with lindane. The bacteria, Paracoccus sp. NITDBR1 and Rhodococcus rhodochrous NITDBS9, have been selected based on their lindane degrading capacity in liquid culture conditions (~80-90 %). The remaining three bacteria were chosen for their auxiliary properties for plant growth promotion, such as nitrogen fixation, phosphate solubilization, indole-3-acetic acid production and ammonia production under in vitro conditions. In this study, market wastes, mainly vegetable wastes, were added to the soil as a biostimulant to form a biomixture for assisting the degradation of lindane by bioaugmentation. Residual lindane was measured at regular intervals of 7 days to monitor the biodegradation process. It was observed that the consortium could degrade ~80% of 50 mg kg^-1 lindane in soil which was further increased in the biomixture after six weeks of incubation. Bioassays performed on plant seeds and cytotoxicity studies performed on human skin fibroblast and HCT116 cell lines revealed that the groups contaminated with lindane and treated with the bacterial consortium showed lower toxicity than their respective controls without any bacteria. Hence, the use of both pesticide degrading and plant growth-promoting bacteria in a consortium can be a promising strategy for improved bioremediation against chemical pesticides, particularly in soil and agricultural fields, simultaneously enhancing crop productivity in those contaminated soil.

Evaluation of the sequential coupling of a bacterial treatment with a physicochemical process for the remediation of wastewater containing Cr and organic pollutants

A restoration strategy was developed for the treatment of two artificial liquid systems (Minimal Medium, MM, and Water Carbon Nitrogen, WCN) contaminated with Cr(VI), lindane (γ-HCH), phenanthrene (Phe), and reactive black 5 (RB5), through the use of an actinobacteria consortium, coupled with a physicochemical treatment using a column filled with nano-scale zero valent iron particles immobilized on dried Macrocystis pyrifera algae biomass. The Sequential Treatment A (ST_A: physicochemical followed by biological method) removed the three organic compounds with different effectiveness; however, it was very ineffective for Cr(VI) removal. The Sequential Treatment B (ST_B: biological followed by the physicochemical method) removed the four compounds with variable efficiencies. The removal of γ-HCH, Phe, and RB5 in both effluents did not present significant differences, regardless of the sequential treatment used. The highest removal of Cr(VI) and total Cr was observed in MM and WCN, respectively. Ecotoxicity tests (L. sativa) of the effluents treated with both methodological couplings demonstrated that the toxicity of WCN only decreased at the end of ST_A, while that of MM decreased at all stages of both sequential treatments. Therefore, MM would be more appropriate to perform both treatments.

Evaluation in the performance of the biodegradation of herbicide diuron to high concentrations by Lysinibacillus fusiformis acclimatized by sequential batch culture

We evaluated and characterized the biodegradation of the herbicide diuron in its commercial form above its saturation concentration by Lysinibacillus fusiformis acclimatized by sequential batch culturing. Acclimatization was carried out in eight cycles in liquid culture, improving the capacity of L. fusiformis to remove diuron from 55.13 ± 1.3% in the first batch to 87.2 ± 0.11% in the eighth batch. Diuron biosorption was characterized with Langmuir and Freundlich isotherms, obtaining a maximum biosorption (q_max) of 0.00885 mg mg^-1. In diuron biodegradation assays, a consumption substrate biomass yield (Y_SD/X) of 6.266 mg mg^-1 was obtained, showing that biodegradation was the main mechanism in diuron removal. Diuron biodegradation by L. fusiformis was characterized by the Monod model, with a maximum specific growth rate (μ_max) of 0.0245 h^-1 and an affinity constant (K_SD) of 344.09 mg L^-1. A low accumulation of 3,4-dichloroaniline with the production of chloride ions indicated dechlorination when diuron was present at high concentrations. A phytotoxic assay conducted with Lactuca sativa showed that the toxicity of an effluent with diuron at 250 mg L^-1 decreased when it was pretreated with acclimatized L. fusiformis. Acclimatization by sequential batch culturing improved the ability of L. fusiformis to biodegrade diuron at high concentrations, showing potential in the bioremediation of diuron-contaminated sites.

Bioremediation of lindane-contaminated soils by combining of bioaugmentation and biostimulation: Effective scaling-up from microcosms to mesocosms

The scaling-up of lindane-contaminated soils bioremediation from microcosms to mesocosms bioaugmentated with an actinobacteria quadruple culture and biostimulated with sugarcane filter cake (SCFC) was surveyed. Mesocosms of silty loam soil, clayey soil, and sandy soil were polluted with the pesticide, bioaugmented with the mixed culture, biostimulated with adequate amounts of 0.5 mm SCFC particles, and assessed during 63 days maintaining environmental parameters with minimal intervention. Samples were taken to determine residual lindane, heterotrophic microorganisms, enzymatic activities, and bioremediation effectiveness using ecotoxicity tests with Raphanus sativus, Lactuca sativa, and Lycopersicon esculentum. The bioaugmentation and biostimulation of the three soils improved lindane removal, microbial counts, and enzymatic activities, and reduced pesticide T_1/2, regarding the values obtained in non-bioremediated controls. The removal process was significantly affected by the soil type, and the highest pesticide dissipation (82.6%) was detected in bioremediated sandy soil. Ecotoxicity tests confirmed the bioremediation success through a rise in the vigor index of seedlings compared to non-treated soils (R. sativus: 12-22%; L. sativa: 12-20%; L. esculentum: 30-45%). Finally, scanning electron microscopy corroborated soil colonization by actinobacteria. Successful scaling-up of the combined application of an actinobacteria quadruple culture and SCFC as an appropriate strategy for restoring lindane-polluted soils at mesocosms-scale was confirmed.

Performance of a continuous stirred tank bioreactor employing an immobilized actinobacteria mixed culture for the removal of organophosphorus pesticides

In this study, we evaluated polyurethane foam (PF), volcanic rock (VR), and a modified plastic cap (MPC) as supports for the immobilization of organophosphorus (OP) pesticide-degrading actinobacterial strains. The colonization and activity of four streptomycetes were favoured by PF, which was selected as the carrier to use in a continuous stirred tank bioreactor (CSTR) that can be operated at increasing inflows of a pesticide mixture that contains the insecticides chlorpyrifos (CP) and diazinon (DZ). Our results demonstrate that the CSTR can be operated at flow rates of 10 and 40 mL h^-1 with greater than 85% removal of the pesticides in the short term. A significant decrease in the efficiency of CP removal was observed at the highest inflows into the reactor. The CP and DZ loading rates in the bioreactor ranged from 0.44 to 1.68 mg L^-1 h^-1 and from 0.50 to 2.17 mg L^-1 h^-1, respectively. Although the treated wastewater exhibited moderate toxicity for Raphanus sativus, a bioreactor inoculated with a mixed culture formed by Streptomyces spp. strains AC5, AC9, GA11 and ISP13 may provide an effective biotechnological strategy for the reduction of OP pesticide residues produced during agronomic and manufacturing practices and therefore prevent environmental pesticidal pollution.

Insights Into the Biodegradation of Lindane (γ-Hexachlorocyclohexane) Using a Microbial System

Lindane (γ-hexachlorocyclohexane) is an organochlorine pesticide that has been widely used in agriculture over the last seven decades. The increasing residues of lindane in soil and water environments are toxic to humans and other organisms. Large-scale applications and residual toxicity in the environment require urgent lindane removal. Microbes, particularly Gram-negative bacteria, can transform lindane into non-toxic and environmentally safe metabolites. Aerobic and anaerobic microorganisms follow different metabolic pathways to degrade lindane. A variety of enzymes participate in lindane degradation pathways, including dehydrochlorinase (LinA), dehalogenase (LinB), dehydrogenase (LinC), and reductive dechlorinase (LinD). However, a limited number of reviews have been published regarding the biodegradation and bioremediation of lindane. This review summarizes the current knowledge regarding lindane-degrading microbes along with biodegradation mechanisms, metabolic pathways, and the microbial remediation of lindane-contaminated environments. The prospects of novel bioremediation technologies to provide insight between laboratory cultures and large-scale applications are also discussed. This review provides a theoretical foundation and practical basis to use lindane-degrading microorganisms for bioremediation.

Enhanced bioremediation of lindane-contaminated soils through microbial bioaugmentation assisted by biostimulation with sugarcane filter cake

Lindane is a toxic and persistent organochlorine pesticide, whose extensive use generated its accumulation in different environmental matrices. Bioremediation is a promising technology that can be used combining bioaugmentation and biostimulation processes to soil restoration. The aim of the present work was to determine the conditions of maximum lindane removal by bioaugmentation with an actinobacteria consortium and biostimulation with sugarcane filter cake (SCFC). The assays were carried out on lindane-contaminated silty loam (SLS), clayey (CS), and sandy (SS) soils. Through complete factorial designs, the effects of three abiotic factors (moisture content, proportion and size of SCFC particles) were evaluated on lindane removal. In addition, a response optimizer determined the optimal conditions for pesticide removal in bioaugmented and biostimulated soils, in the range of levels studied for each factor. In these conditions, bioaugmentation of biostimulated soils increased the pesticide removal (SLS: 61.4%, CS: 70.8%, SS: 86.3%), heterotrophic microbial counts, and soil enzymatic activities, and decreased lindane T_1/2, regarding the non-bioaugmented biostimulated controls, after 14 days of assay. The values of these parameters confirmed the efficiency of the bioremediation process. Finally, the viability of the four strains was demonstrated at the end of the assay. The results indicate that the simultaneous application of bioaugmentation with the actinobacteria consortium and biostimulation with SCFC constitutes a promising tool for restoring soils contaminated with lindane, by using the optimal conditions obtained through the factorial designs.

Enhanced Cypermethrin Degradation Kinetics and Metabolic Pathway in Bacillus thuringiensis Strain SG4

Cypermethrin is popularly used as an insecticide in households and agricultural fields, resulting in serious environmental contamination. Rapid and effective techniques that minimize or remove insecticidal residues from the environment are urgently required. However, the currently available cypermethrin-degrading bacterial strains are suboptimal. We aimed to characterize the kinetics and metabolic pathway of highly efficient cypermethrin-degrading Bacillus thuringiensis strain SG4. Strain SG4 effectively degraded cypermethrin under different conditions. The maximum degradation was observed at 32 °C, pH 7.0, and a shaking speed of 110 rpm, and about 80% of the initial dose of cypermethrin (50 mg·L-1) was degraded in minimal salt medium within 15 days. SG4 cells immobilized with sodium alginate provided a higher degradation rate (85.0%) and lower half-life (t1/2) of 5.3 days compared to the 52.9 days of the control. Bioaugmentation of cypermethrin-contaminated soil slurry with strain SG4 significantly enhanced its biodegradation (83.3%). Analysis of the degradation products led to identification of nine metabolites of cypermethrin, which revealed that cypermethrin could be degraded first by cleavage of its ester bond, followed by degradation of the benzene ring, and subsequent metabolism. A new degradation pathway for cypermethrin was proposed based on analysis of the metabolites. We investigated the active role of B. thuringiensis strain SG4 in cypermethrin degradation under various conditions that could be applied in large-scale pollutant treatment.

Coupling of bioaugmentation and biostimulation to improve lindane removal from different soil types

Lindane is an organochlorine pesticide that, due to its persistence in the environment, is still detected in different matrices. Bioremediation using actinobacteria consortia proved to be promising for the restoration of contaminated soils. Another alternative to remove xenobiotics is to use agricultural residues, which stimulates microbial activity, increasing its capacity to degrade organic pollutants. The present work studies the coupling of sugarcane bagasse biostimulation and bioaugmentation with the actinobacteria consortium composed of Streptomyces sp. A2, A5, A11 and M7 on lindane removal in different soil types. In this sense, factorial designs with three factors (proportion and size of sugarcane bagasse particles, and moisture content) were employed. A response optimizer identified the combination of factors levels that jointly allowed obtaining the maximum lindane removal in the evaluated conditions. In the optimal conditions, the effect of the bioremediation process on soil microbiota was studied by evaluating different parameters. The highest lindane removal percentages were detected in biostimulated microcosms bioaugmented with the microbial consortium, which were accompanied by a decrease in lindane half-life respect to the controls. Also, the bioaugmentation of biostimulated microcosms increased the microbial counts and enhanced soil enzymatic activities, corroborating the bioremediation process efficiency. The survival of the four actinobacteria at the end of the assay confirmed the ability of all Streptomyces strains to colonize amended soils. Bioremediation by simultaneous application of biostimulation with sugarcane bagasse and bioaugmentation with the actinobacteria consortium, in the optimized conditions, represents an efficient strategy to restore lindane contaminated soils.

Evaluation of the effectiveness of a bioremediation process in experimental soils polluted with chromium and lindane

Bioremediation using actinobacterium consortia proved to be a promising alternative for the purification of co-contaminated environments. In this sense, the quadruple consortium composed of Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis AB0 has been able to remove significant levels of Cr(VI) and lindane from anthropogenically contaminated soils. However, the effectiveness of the bioremediation process could not be evaluated only by analytical monitoring, which is complex mainly due to the characteristics of the matrix, producing non-quantitative analyte recoveries, or interferences in the detection stage and quantification. However, the effectiveness of the bioremediation process cannot be evaluated only through analytical monitoring, which is complex due mainly to the characteristics of the matrix, to the recoveries of non-quantitative analytes or to interferences in the detection and quantification stage. For this reason, it is essential to have tools of ecological relevance to assess the biological impact of pollutants on the environment. In this context, the objective of this work was to establish the appropriate bioassays to evaluate the effectiveness of a bioremediation process of co-contaminated soils. For this, five model species were studied: four plant species (Lactuca sativa, Raphanus sativus, Lycopersicon esculentum, and Zea mays) and one animal species (Eisenia fetida). On plant species, the biomarkers evaluated were inhibition of germination (IG) and the length of hypocotyls/steam and radicles/roots of the seedling. While on E. fetida, mortality (M), weight lost, coelomocyte concentration and cell viability were tested. These bioindicators and the battery of biomarkers quantified in them showed a different level of sensitivity, from maximum to minimum: E. fetida > L. esculentum > L. sativa > R. sativus ≫>Z. mays. Therefore, E. fetida and L. esculentum and their respective biomarkers were selected to evaluate the effectiveness of the bioremediation process due to the capability of assessing the effect on the flora and the fauna of the soil, respectively. The joint application of these bioindicators in a field scale bioremediation process is a feasible tool to demonstrate the recovery of the quality and health of the soil.

Rhizospheric Microbacterium sp. P27 Showing Potential of Lindane Degradation and Plant Growth Promoting Traits

Lindane is an organochlorine pesticide that is highly persistent in the environment. The amassing of lindane has been identified worldwide and has been found to be very toxic to the environment, human, and animal health. Therefore, urgent consideration and management of the problem is necessary. The current study intends to isolate and identify lindane degrading rhizospheric bacteria from Phragmites karka and to study its degradation kinetics. Also, plant growth promoting potential of the bacterium was evaluated in the presence and absence of studied pesticide. Rhizospheric bacteria were isolated by standard enrichment technique in Mineral Salt Medium. Microbacterium sp. P27 showed the highest degradation percentage, 82.7 ± 1.79% for 50 mg l^-1 lindane, after 15 days. Degradation was also studied at different concentrations of lindane. Maximum degradation was achieved at 10 mg l^-1 followed by 50 mg l^-1 and 100 mg l^-1 lindane. Microbacterium sp. P27 showed positive result for Indole-3-acetic acid production, ammonia production, and 1-aminocyclopropane-1-carboxylate deaminase activity. Presence of lindane revealed a concentration-dependent decrease in plant growth promoting activity. Since the isolated bacterial strain possesses lindane degrading capacity and also other characters that help in plant growth promotion, the isolate can be an important candidate for the progress of bioremediation strategy.

Lindane degradation by root epiphytic bacterium Achromobacter sp. strain A3 from Acorus calamus and characterization of associated proteins

Lindane degrading root epiphytic bacteria were isolated from wetland plant Acorus calamus. Bacterial strain A3 identified as Achromobacter sp. A3, showed maximum degradation potential of 88.7 ± 1.24% for 50 mg l^-1 lindane. Lindane biodegradation was followed by decrease in pH as well as increase in concentration of chloride ions in the culture medium. Lindane degradation potential of Achromobacter sp. A3 was also studied at different concentrations of lindane. Maximum degradation was at 10 mg l^-1 followed by 50 mg l^-1 and 100 mg l^-1 lindane. Also, lindane induced proteins were studied using SDS-PAGE. The induced proteins were identified as alpha/beta hydrolase fold-3 domain-containing protein, involved in lindane hydrolysis and extracellular solute-binding family protein having role in transmembrane transport of lindane for utilization of lindane by bacteria. The appearance of unique polypeptides in lane corresponding to media supplemented with lindane showed that the exposure of bacterial cells to lindane has resulted in regulative expression of certain proteins. So far as known, this is the first report to isolate and study lindane degrading root epiphytic bacteria from A. calamus.

Strengthening calcium alginate microspheres using polysulfone and its performance evaluation: Preparation, characterization and application for enhanced biodegradation of chlorpyrifos

Bacterial cell immobilization offer considerable advantages over traditional biotreatment systems using free cells. Calcium alginate matrix usually used for bacterial immobilization is susceptible to biodegradation in harsh environment. Current study aimed to produce and characterize stable macrocapsules (MCs) of Chlorpyrifos (CP) degrading bacterial consortium using biocompatible calcium alginate matrix coupled with environmentally stable polysulfone. In current study bacterial consortium capable of CP biodegradation was immobilized using calcium alginate in a form of microcapsule (MC) reinforced by being coated with a synthetic polymer polysulfone (PSf) through phase inversion. Consortium comprised of five bacterial strains was immobilized using optimized concentration of sodium alginate (2.5gL^-1), calcium chloride (6gL^-1), biomass (600mgL^-1) and polysulfone (10gL^-1). It has been observed that MCs have high thermal, pH and chemical stability than CAMs. In synthetic media complete biodegradation of CP (100-600mgL^-1) was achieved using macrocapsules (MCs) within 18h. CAMs could be reused effectively only upto 5cycles, contrary to this MCs could be used 13 times to achieve more than >96% CP degradation. Shelf life and reusability studies conducted for MCs indicated unaltered biomass retention and CP biodegradation activity (95%) over 16weeks of storage. MCs achieved complete biodegradation of CP (536mgL^-1) in real industrial wastewater and reused several times effectively. Metabolites (3,5,6-trichloro-2-pyridinol (TCP), 3,5,6-trichloro-2-methoxypyridine (TMP) and diethyl-thiophosphate (DETP) were traced using GC-MS and possible metabolic pathway was constructed. Study indicated MCs could be used for cleanup of CP contaminated wastewater repeatedly, safely, efficiently for a longer period of time.

Organophosphorus pesticide mixture removal from environmental matrices by a soil Streptomyces mixed culture

The current study aimed to evaluate the removal of a pesticide mixture composed of the insecticides chlorpyrifos (CP) and diazinon (DZ) from liquid medium, soil and a biobed biomixture by a Streptomyces mixed culture. Liquid medium contaminated with 100 mg L^-1 CP plus DZ was inoculated with the Streptomyces mixed culture. Results indicated that microorganisms increased their biomass and that the inoculum was viable. The inoculum was able to remove the pesticide mixture with a removal rate of 0.036 and 0.015 h^-1 and a half-life of 19 and 46 h^-1 for CP and DZ, respectively. The sterilized soil and biobed biomixture inoculated with the mixed culture showed that Streptomyces was able to colonize the substrates, exhibiting an increase in population determined by quantitative polymerase chain reaction (q-PCR), enzymatic activity dehydrogenase (DHA) and acid phosphatase (APP). In both the soil and biomixture, limited CP removal was observed (6-14%), while DZ exhibited a removal rate of 0.024 and 0.060 day^-1 and a half-life of 29 and 11 days, respectively. Removal of the organophosphorus pesticide (OP) mixture composed of CP and DZ from different environmental matrices by Streptomyces spp. is reported here for the first time. The decontamination strategy using a Streptomyces mixed culture could represent a promising alternative to eliminate CP and DZ residues from liquids as well as to eliminate DZ from soil and biobed biomixtures.

Actinobacteria consortium as an efficient biotechnological tool for mixed polluted soil reclamation: Experimental factorial design for bioremediation process optimization

The objective of the present work was to establish optimal biological and physicochemical parameters in order to remove simultaneously lindane and Cr(VI) at high and/or low pollutants concentrations from the soil by an actinobacteria consortium formed by Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis AB0. Also, the final aim was to treat real soils contaminated with Cr(VI) and/or lindane from the Northwest of Argentina employing the optimal biological and physicochemical conditions. In this sense, after determining the optimal inoculum concentration (2gkg^-1), an experimental design model with four factors (temperature, moisture, initial concentration of Cr(VI) and lindane) was employed for predicting the system behavior during bioremediation process. According to response optimizer, the optimal moisture level was 30% for all bioremediation processes. However, the optimal temperature was different for each situation: for low initial concentrations of both pollutants, the optimal temperature was 25°C; for low initial concentrations of Cr(VI) and high initial concentrations of lindane, the optimal temperature was 30°C; and for high initial concentrations of Cr(VI), the optimal temperature was 35°C. In order to confirm the model adequacy and the validity of the optimization procedure, experiments were performed in six real contaminated soils samples. The defined actinobacteria consortium reduced the contaminants concentrations in five of the six samples, by working at laboratory scale and employing the optimal conditions obtained through the factorial design.

Streptomyces sp. is a powerful biotechnological tool for the biodegradation of HCH isomers: biochemical and molecular basis

Actinobacteria are well-known degraders of toxic materials that have the ability to tolerate and remove organochloride pesticides; thus, they are used for bioremediation. The biodegradation of organochlorines by actinobacteria has been demonstrated in pure and mixed cultures with the concomitant production of metabolic intermediates including γ-pentachlorocyclohexene (γ-PCCH); 1,3,4,6-tetrachloro-1,4-cyclohexadiene (1,4-TCDN); 1,2-dichlorobenzene (1,2-DCB), 1,3-dichlorobenzene (1,3-DCB), or 1,4-dichlorobenzene (1,4-DCB); 1,2,3-trichlorobenzene (1,2,3-TCB), 1,2,4-trichlorobenzene (1,2,4-TCB), or 1,3,5-trichlorobenzene (1,3,5-TCB); 1,3-DCB; and 1,2-DCB. Chromatography coupled to mass spectrometric detection, especially GC-MS, is typically used to determine HCH-isomer metabolites. The important enzymes involved in HCH isomer degradation metabolic pathways include hexachlorocyclohexane dehydrochlorinase (LinA), haloalkane dehalogenase (LinB), and alcohol dehydrogenase (LinC). The metabolic versatility of these enzymes is known. Advances have been made in the identification of actinobacterial haloalkane dehydrogenase, which is encoded by linB. This knowledge will permit future improvements in biodegradation processes using Actinobacteria. The enzymatic and genetic characterizations of the molecular mechanisms involved in these processes have not been fully elucidated, necessitating further studies. New advances in this area suggest promising results. The scope of this paper encompasses the following: (i) the aerobic degradation pathways of hexachlorocyclohexane (HCH) isomers; (ii) the important genes and enzymes involved in the metabolic pathways of HCH isomer degradation; and (iii) the identification and quantification of intermediate metabolites through gas chromatography coupled to mass spectrometry (GC-MS).

Enhancing methyl parathion degradation by the immobilization of Burkholderia sp. isolated from agricultural soils

Organophosphate pesticides are of great interest for research because they are currently the most commonly used pesticides. In this study, a bacterial strain capable of completely degrading methyl parathion (MP) was isolated from agricultural soils in central Mexico. This strain was designated strain S5-2 and was identified as Burkholderia cenocepacia. To increase degradation yields, cells were immobilized on three different supports: powdered zeolite and Opuntia sp. and Agave sp. fibers. The results indicated a significant increase in MP hydrolysis and p-nitrophenol (PNP) degradation with immobilized cells compared to free cell cultures. Furthermore, immobilized cells were capable of withstanding and degrading higher concentrations of PNP compared to cell suspension cultures. The cell viability in the free cell cultures, as well as PNP degradation, was affected at concentrations greater than 25 mg/L. In contrast, cells immobilized on Opuntia sp. and Agave sp. fibers completely degraded PNP at concentrations of 100 mg/L. To verify that MP solution toxicity was decreased by B. cenocepacia strain S5-2 via pesticide degradation, we measured the acetylcholinesterase activity, both before and after treatment with bacteria. The results demonstrate that the activity of acetylcholinesterase was unaffected after MP degradation by bacteria.

Actinobacteria: Current research and perspectives for bioremediation of pesticides and heavy metals

Actinobacteria exhibit cosmopolitan distribution since their members are widely distributed in aquatic and terrestrial ecosystems. In the environment they play relevant ecological roles including recycling of substances, degradation of complex polymers, and production of bioactive molecules. Biotechnological potential of actinobacteria in the environment was demonstrated by their ability to remove organic and inorganic pollutants. This ability is the reason why actinobacteria have received special attention as candidates for bioremediation, which has gained importance because of the widespread release of contaminants into the environment. Among organic contaminants, pesticides are widely used for pest control, although the negative impact of these chemicals in the environmental balance is increasingly becoming apparent. Similarly, the extensive application of heavy metals in industrial processes lead to highly contaminated areas worldwide. Several studies focused in the use of actinobacteria for cleaning up the environment were performed in the last 15 years. Strategies such as bioaugmentation, biostimulation, cell immobilization, production of biosurfactants, design of defined mixed cultures and the use of plant-microbe systems were developed to enhance the capabilities of actinobacteria in bioremediation. In this review, we compiled and discussed works focused in the study of different bioremediation strategies using actinobacteria and how they contributed to the improvement of the already existing strategies. In addition, we discuss the importance of omic studies to elucidate mechanisms and regulations that bacteria use to cope with pollutant toxicity, since they are still little known in actinobacteria. A brief account of sources and harmful effects of pesticides and heavy metals is also given.

Effect of coating on the environmental applications of zero valent iron nanoparticles: the lindane case

Commercial stabilized slurry of zero-valent iron nanoparticles (nZVI) as well as laboratory-synthesized polymer-stabilized NZVI nanoparticles were used for lindane (γ-hexachlorocyclohexane) degradation studies in aqueous solution. In the present study, polymer-stabilized iron nanoparticles were stabilized using polyethylene glycol (PEG, Mn ~400 and ~950-1050) and polytetrahydrofuran (PTHF, Mn ~650). To study the effectiveness of the different nanoparticles, a quantitative monitorization of lindane degradation by using solid-phase extraction (SPE) and a qualitative measurement of generated volatile by-products by headspace-solid phase microextraction (HS-SPME) followed by GC/MS were carried out. The obtained data were compared and contrasted with the results obtained in previous work. Results showed that the nanoparticles studied in this work possess superior dechlorination performance compared with previous observations. The freshly prepared Fe(0)-PEG400, Fe(0)-PEG1050 and Fe(0)-PTHF exhibited high reactivity during the dechlorination process of lindane in a very short time. The results obtained with the synthesized nanoparticles were similar to those obtained with commercial nanoparticles. However, in all cases reactivity decreased at reaction's late stage. Degradation of lindane by the studied nanoparticles removed 99.9% of the lindane initial concentration after 72h, except for Fe(0)-PTHF nanoparticles, for which the reaction stopped after 5min. In all cases, the reaction followed a second order kinetics. Finally, comparing the results from this study with our previous work, where different nature polymers were considered (Fe(0)-CMC, Fe(0)-PAA and Fe(0)-PAP), more gradual degradation profile of lindane was observed for Fe(0)-PAA and Fe(0)-CMC. It should be noted that in the present case, the reaction of lindane was speeded up with commercial and Fe(0)-PEG nanoparticles. Nevertheless, in the later case, the composition of by-products was affected by the presence of partially degraded intermediates. Taking into account the current technologies, the high removal rates obtained and the acceptable degradation times required, the proposed technology is suitable for its aimed purpose.

Evidence of α-, β- and γ-HCH mixture aerobic degradation by the native actinobacteria Streptomyces sp. M7

The organochlorine insecticide γ-hexachlorocyclohexane (γ-HCH, lindane) and its non-insecticidal α- and β-isomers continue to pose serious environmental and health concerns, although their use has been restricted or completely banned for decades. In this study we report the first evidence of the growth ability of a Streptomyces strain in a mineral salt medium containing high doses of α- and β-HCH (16.6 mg l(-1)) as a carbon source. Degradation of HCH isomers by Streptomyces sp. M7 was investigated after 1, 4, and 7 days of incubation, determining chloride ion release, and residues in the supernatants by GC with µECD detection. The results show that both the α- and β-HCH isomers were effectively metabolized by Streptomyces sp. M7, with 80 and 78 % degradation respectively, after 7 days of incubation. Moreover, pentachlorocyclohexenes and tetrachlorocyclohexenes were detected as metabolites. In addition, the formation of possible persistent compounds such as chlorobenzenes and chlorophenols were studied by GC-MS, while no phenolic compounds were detected. In conclusion, we have demonstrated for the first time that Streptomyces sp. M7 can degrade α- and β-isomers individually or combined with γ-HCH and could be considered as a potential agent for bioremediation of environments contaminated by organochlorine isomers.