Chlorpyrifos degradation by the cyanobacterium Synechocystis sp. strain PUPCCC 64

In situ chlorpyrifos (CPF) degradation by Acrobeloides maximus: Insights from chromatographic analysis

The objective of this study was to evaluate the efficiency of nematodes in zooremediation of chlorpyrifos (CPF), an organophosphate pesticide. The nematode population Acrobeloides maximus (A. maximus) was employed for bioremediation, converting CPF into non-toxic residues. Optimal growth conditions for mass production of A. maximus were achieved by maintaining a temperature of 25 °C, pH 8, and supplementing the culture medium with plant nutrients. The nematodes were then immobilized within sodium alginate beads. The efficacy of the degradation process was assessed using various analytical techniques, including UV-Visible spectroscopy, HPTLC, FTIR, and LC-MS, confirming the successful breakdown of CPF. The bioreactor demonstrated a complete degradation efficiency of CPF exceeding 99%. Additionally, LC-MS analysis was conducted to elucidate the degradation pathway based on the formation of intermediates. These results underscore the potential of A. maximus as a sustainable organism for addressing environmental contamination arising from CPF pesticide.

Bioremediation of chlorpyrifos residues using some indigenous species of bacteria and fungi in wastewater

Pollutants cause a huge problem for humans, animals, plants, and various ecosystems, especially water resources. Agricultural, domestic, and industrial waste effluents change the water quality and affect living microorganisms. Therefore, the current study aimed to identify possible microorganisms in wastewater as potential bioremediation agents of pesticide residues. Wastewater samples were collected from El-Khairy agricultural drainage, which receives agricultural and domestic wastes. Bacteria and fungi species were isolated as clean cultures. Wastewater samples were analyzed for pesticide residues via gas chromatography-mass spectroscopy (GC-MS) system. Results uncovered the presence of ten pesticides ranging from 0.0817 to 28.162 µg/l, and the predominant pesticide was chlorpyrifos. Along with that, about nine species (3 bacterial and 6 fungal) were relatively efficient in the removal of chlorpyrifos residues up to 2000 µg/l with removal percentages ranging from 24.16 to 80.93% under laboratory conditions. Two bacterial isolates proficiently degraded significant amounts of chlorpyrifos: Bacillus cereus strain PC2 (GenBank accession No. MZ314010) and Streptomyces praecox strain SP1 (GenBank accession No. MZ314009). In-site bacterial and fungal isolates defined in the current study were proficient in cleaning wastewater of chlorpyrifos pesticide residues.

Uptake of endosulfan isomers from soils by leafy vegetable lettuce: A comparative study between model-predicted and field-experimented results

The organochlorine insecticide endosulfan has been classified as a persistent organic pollutant due to its long persistence and high toxicity, and banned in most countries. However, endosulfan residues are still detected in various environmental sites (even in non-agricultural areas) and have a likelihood to return to agricultural soils through various routes. In this study, time-dependent uptake of α- and β-isomers of endosulfan by lettuce from soils was estimated using theoretical models which include parameters describing sorption/dissipation in soil and plants, plant transpiration, root-soil transfer, and plant growth. A chemical-specific residue (CSR) model developed in a previous study was used as a sub-model to estimate the portion of endosulfan residues in soils ready to be absorbed by lettuce, and the accuracy of the CSR model was verified by properly estimating concentrations of endosulfan isomers in soils with different organic matters; a low mean deviation (18.8 %) was observed between the modeled and measured values. Modeled results of β-endosulfan using a soil-lettuce uptake model satisfactorily matched the experimentally measured results, with a moderate correlation (R2 > 0.79) and a low residual error (0.42) against a mean factor of -1.04. However, the uptake model showed the low potential to predict the soil-lettuce uptake of α-endosulfan (176.3 % mean deviation), probably due to not considering an intrinsic trait of β-isomer converting to α-isomer. Although the improvement with more sophisticated parameters is needed, the plant uptake model developed in this study could be utilized to predict soil-lettuce uptake of at least β-endosulfan and as a model template that may apply for other types of plants and contaminants.

Green synthesis of rGO-AgNP composite using Curcubita maxima extract for enhanced photocatalytic degradation of the organophosphate pesticide chlorpyrifos

In this study, Curcubita maxima leaves are used as a novel source for green synthesis of reduced graphene oxide - silver nanoparticle composite in a single pot. Characterization of the novel phyto source-driven composite was performed by UV-visible spectroscopy, Fourier transform infrared analysis, X-ray diffraction analysis, and field emission scanning electron microscopic methods. The assessment of degradation effect of chlorpyrifos by the synthesized nanocomposite was performed. The photocatalytic activity of the composite was demonstrated through two different processes as adsorption under room temperature and photocatalysis in the presence of sunlight. Different parameters such as pH, time, photocatalyst dose and pesticide concentration were optimized. The adsorption isotherms governing the photocatalytic adsorption process were investigated to predict the adsorption capacity of the synthesized nanocomposite. In addition, the results of antimicrobial activity of the nanocomposite against gram-positive, gram-negative bacteria and antifungal activity were also been found to be highly promising to utilize this composite for the removal of microbial contaminations in wastewater treatment.

Microbial Remediation: A Promising Tool for Reclamation of Contaminated Sites with Special Emphasis on Heavy Metal and Pesticide Pollution: A Review

Heavy metal and pesticide pollution have become an inevitable part of the modern industrialized environment that find their way into all ecosystems. Because of their persistent nature, recalcitrance, high toxicity and biological enrichment, metal and pesticide pollution has threatened the stability of the environment as well as the health of living beings. Due to the environmental persistence of heavy metals and pesticides, they get accumulated in the environs and consequently lead to food chain contamination. Therefore, remediation of heavy metals and pesticide contaminations needs to be addressed as a high priority. Various physico-chemical approaches have been employed for this purpose, but they have significant drawbacks such as high expenses, high labor, alteration in soil properties, disruption of native soil microflora and generation of toxic by-products. Researchers worldwide are focusing on bioremediation strategies to overcome this multifaceted problem, i.e., the removal, immobilization and detoxification of pesticides and heavy metals, in the most efficient and cost-effective ways. For a period of millions of evolutionary years, microorganisms have become resistant to intoxicants and have developed the capability to remediate heavy metal ions and pesticides, and as a result, they have helped in the restoration of the natural state of degraded environs with long term environmental benefits. Keeping in view the environmental and health concerns imposed by heavy metals and pesticides in our society, we aimed to present a generalized picture of the bioremediation capacity of microorganisms. We explore the use of bacteria, fungi, algae and genetically engineered microbes for the remediation of both metals and pesticides. This review summarizes the major detoxification pathways and bioremediation technologies; in addition to that, a brief account is given of molecular approaches such as systemic biology, gene editing and omics that have enhanced the bioremediation process and widened its microbiological techniques toward the remediation of heavy metals and pesticides.

Growth, respiratory activity and chlorpyrifos biodegradation in cultures of Azotobacter vinelandii ATCC 12837

This study aimed to evaluate the growth, respiratory activity, and biodegradation of chlorpyrifos in cultures of Azotobacter vinelandii ATCC 12837. A strategy based on the modification of culture media and aeration conditions was carried out to increase the cell concentration of A. vinelandii, in order to favor and determine its tolerance to chlorpyrifos and its degradation ability. The culture in shaken flasks, using sucrose as a carbon source, significantly improved the growth compared to media with mannitol. When the strain was cultivated under oxygen-limited (5.5, 11.25 mmol L⁻¹ h⁻¹) and no-oxygen-limited conditions (22 mmol L⁻¹ h⁻¹), the growth parameters were not affected. In cultures in a liquid medium with chlorpyrifos, the bacteria tolerated a high pesticide concentration (500 ppm) and the growth parameters were improved even under conditions with a reduced carbon source (sucrose 2 g L⁻¹). The strain degraded 99.6% of chlorpyrifos at 60 h of cultivation, in co-metabolism with sucrose; notably, A. vinelandii ATCC 12837 reduced by 50% the initial pesticide concentration in only 6 h (DT₅₀).

Removal of chlorpyrifos and its hydrolytic metabolite in microcosm-scale constructed wetlands under soda saline-alkaline condition: Mass balance and intensification strategies

Chlorpyrifos (CP) is a typical organophosphorus insecticide, which poses serious threats to the natural environment and human health. Strategies for the fast elimination of CP and its toxic hydrolytic metabolite 3,5,6-trichloro-2(1H)-pyridianol (TCP) in drainage water are urgently needed. The fate of CP and TCP in microcosm-scale subsurface batch constructed wetlands (SSBCWs) was quantified with different macrophyte species under soda saline-alkaline (SSA) condition and effective intensification strategies were developed. The macrophyte species Canna indica outperformed Phragmites australis and Typha orientalis for CP and TCP removal in SSBCWs. Mass balance calculation indicates the fate of CP in SSBCWs was residue in water (≤8%), alkaline hydrolysis (18.93-57.42%), microbial degradation (37.75-61.91%), substrate adsorption (~4-14%), and macrophyte uptake (≤3%). The addition of ferric-carbon (Fe-C) as a substrate amendment in SSBCWs increased the CP removal percentage by 35% and reduced the effluent TCP concentration by ~70% during Day 1-4 on average compared with the unintensified control. Fe-C addition simplified the microbial community diversity, while increasing the relative abundance of Proteobacteria which tolerates the microelectrolytic environment. A single application of liquid microbial agent improved CP removal percentage by 84% and decreased the effluent TCP concentration by two orders of magnitude during Day 1-4. The hydraulic retention time for thorough removal of TCP reduced from over 8 d to 4 d. Although only two dominant microbial genera (i.e., Sphingomonas and Pseudomonas) adapted to the environment with CP and SSA, they accelerated CP and TCP degradation via their own metabolism and co-metabolism with other indigenous microorganisms.

Potential of formulated Dyadobacter jiangsuensis strain 12851 for enhanced bioremediation of chlorpyrifos contaminated soil

Chlorpyrifos (O, O-diethyl O-3, 5, 6-trichloropyridin-2-yl phosphorothioate) is a toxic and chlorinated organic contaminant in soils across the globe. The present study examines the chlorpyrifos (CP) degrading potential of gram-negative bacterium Dyadobacter jiangsuensis (MTCC 12851), to be a promising and sustainable remedial approach. The proliferation of D. jiangsuensis in the chlorpyrifos spiked minimal salt media indicated the ability of this strain to utilize CP as a sole carbon source and also confirmed the utilization of 3,5,6- trichloro-2-pyridinyl (TCP) through silver nitrate assay. The strain 12851 degraded 80.36% and 76.93% chlorpyrifos (CP) in aqueous medium and soil environment, respectively. The water dispersible granules (WDG) of 45% (v/w) inoculum (bacterial suspension) were developed using talcum powder, acacia gum and alginic acid as key ingredients. The formulated strain (12851) achieved 21.13% enhanced CP degradation in soil under microcosm condition as compared to the unformulated one on 15th day of the treatment. The intermediate metabolites namely 3,5,6-trichloro-2-pyridinol (TCP), tetrahydropyridine, thiophosphate and phenol, 1, 3-bis (1,1-dimethylethyl) were detected during the CP degradation. The current investigation reveals D. jiangsuensis as a potential microbe for CP degradation and opens up the possibility of exploiting its formulations to remediate the CP polluted soils.

Ferrihydrite Reduction by Photosynthetic Synechocystis sp. PCC 6803 and Its Correlation With Electricity Generation

Microbial extracellular electron transfer (EET) to solid-state electron acceptors such as anodes and metal oxides, which was originally identified in dissimilatory metal-reducing bacteria, is a key process in microbial electricity generation and the biogeochemical cycling of metals. Although it is now known that photosynthetic microorganisms can also generate (photo)currents via EET, which has attracted much interest in the field of biophotovoltaics, little is known about the reduction of metal (hydr)oxides via photosynthetic microbial EET. The present work quantitatively assessed the reduction of ferrihydrite in conjunction with the EET of the photosynthetic microbe Synechocystis sp. PCC 6803. Microbial reduction of ferrihydrite was found to be initiated in response to light but proceeded at higher rates when exogenous glucose was added, even under dark conditions. These results indicate that current generation from Synechocystis cells does not always need light irradiation. The qualitative trends exhibited by the ferrihydrite reduction rates under various conditions showed significant correlation with those of the microbial currents. Notably, the maximum concentration of Fe(II) generated by the cyanobacterial cells under dark conditions in the presence of glucose was comparable to the levels observed in the photic layers of Fe-rich microbial mats.

Insights into the microbial degradation and catalytic mechanisms of chlorpyrifos

Chlorpyrifos is extensively used worldwide as an insecticide to control various insect pests. Long-term and irregular applications of chlorpyrifos have resulted in large-scale soil, groundwater, sediment, and air pollution. Numerous studies have shown that chlorpyrifos and its major intermediate metabolite 3,5,6-trichloropyridinol (TCP) accumulate in non-target organisms through biomagnification and have a strong toxic effect on non-target organisms, including human beings. Bioremediation based on microbial metabolism is considered an eco-friendly and efficient strategy to remove chlorpyrifos residues. To date, a variety of bacterial and fungal species have been isolated and characterized for the biodegradation of chlorpyrifos and TCP. The metabolites and degradation pathways of chlorpyrifos have been investigated. In addition, the chlorpyrifos-degrading enzymes and functional genes in microbes have been reported. Hydrolases can catalyze the first step in ester-bond hydrolysis, and this initial regulatory metabolic reaction plays a key role in the degradation of chlorpyrifos. Previous studies have shown that the active site of hydrolase contains serine residues, which can initiate a catalytic reaction by nucleophilic attack on the P-atom of chlorpyrifos. However, few reviews have focused on the microbial degradation and catalytic mechanisms of chlorpyrifos. Therefore, this review discusses the deep understanding of chlorpyrifos degradation mechanisms with microbial strains, metabolic pathways, catalytic mechanisms, and their genetic basis in bioremediation.

Dissipation of pyridaphenthion by cyanobacteria: Insights into cellular degradation, detoxification and metabolic regulation

Excessive use of organophosphorus pesticides such as pyridaphenthion (PY) to constrain insects induced crop loss, results in soil and water sources contamination. Cyanobacteria are sensitive biological indicators and promising tools for bioremediation of soil and water pollutants. To understand PY toxicity, detoxification and degradation in cyanobacteria, we performed a comparative study in the two diazotrophic cyanobacteria; Anabaena laxa and Nostoc muscorum. They were exposed to mild (5 mg/L) and high (10 mg/L) concentrations of PY for 7 days. Compared to A. laxa, N. muscorum efficiently showed high PY accumulation and degradation to a safe environmentally product; 6-hydroxy-2-phenylpyridazin-3(2 H)-one. PY inhibited cell growth and reduced Chl a content and photosynthesis related enzymes (PEPC and RuBisCo) activities in both species, but to less extend in N. muscorum. It also induced oxidative damage, particularly in A. laxa, as indicated by high H₂O₂, lipid peroxidation and protein oxidation levels and increased NADPH oxidase enzyme activity. N. muscorum invested more in antioxidants induction, i.e., induced ascorbate and glutathione cycle, however, these antioxidants increments in A. laxa were less pronounced. Overall, this study provides more in-deep insights into the PY toxicity and the role of N. muscorum as a promising PY remediator.

Rapid biodegradation of chlorpyrifos by plant growth-promoting psychrophilic Shewanella sp. BT05: An eco-friendly approach to clean up pesticide-contaminated environment

The present study explores the rapid chlopyrifos (CPs) biodegradation potential of plant growth promoting (PGP) psychrophilic bacteria isolated from brackish water by enrichment culture technique. Based on biochemical tests and 16 S rDNA sequencing the isolate was identified as Shewanella sp. The isolate Shewanella BT05 showed significant growth rate in various concentrations of (10-50 mg/L) CPs. The isolate produced plant growth promoting factors, IAA (20.8 ± 1.2 and 15.4 ± 1.0 μg/mL) and siderophores (60.67 ± 1.2 and 57.5 ± 0.9%) in the absence and presence of CPs. Further, the isolate BT05 solublized phosphate (16.5 ± 1.0 and 12.0 ± 1.0 mm in size respectively), and produce hydrogen cyanide (excellent and moderate) in the presence and absence of CPs. The isolate BT05 degraded 94.3, 91.8, 87.9, 82.6, and 80.5% of CPs at 10, 20, 30, 40, and 50 mg/L, respectively, within 24 h. Further, the media conditions were optimized for enhanced CPs removal and observed 93% removal in the presence of 3.5% glucose in pH 7.0 at 32.5 °C. Fourier-transform infrared spectroscopy and high-performance liquid chromatography results indicated the role for Shewanella BT05 in the biomineralization of CPs. The results suggested the isolate BT05 could be used for CPs removal as well as PGP activity in contaminated soil.

Comparative Genomics of a Paddy Field Bacterial Isolate Ochrobactrum sp. CPD-03: Analysis of Chlorpyrifos Degradation Potential

Ochrobactrum genus is known to catabolize aromatic compounds. This study reports a complete genome sequence of Ochrobactrum sp. CPD-03 (~ 4.6 Mb of chromosomal features) responsible for chlorpyrifos (CP) isolated form a paddy field (20.3588° N, 85.8333° E) in Bhubaneswar, India. A comparative genomics approach was performed between CPD-03 and eight closely related genomes of other Ochrobactrum strains in order to deepen our knowledge, to establish its phylogenetic and functional relationships. The involvement of CP degrading genes indicated a versatile role of CPD-03 in additional field trails. This research would provide the genetic information for its use in natural environment for the depletion of organophosphorus (OP) compounds.

Rapid Biodegradation of the Organophosphorus Insecticide Chlorpyrifos by Cupriavidus nantongensis X1T

Chlorpyrifos was one of the most widely used organophosphorus insecticides and the neurotoxicity and genotoxicity of chlorpyrifos to mammals, aquatic organisms and other non-target organisms have caused much public concern. Cupriavidus nantongensis X1^T, a type of strain of the genus Cupriavidus, is capable of efficiently degrading 200 mg/L of chlorpyrifos within 48 h. This is ~100 fold faster than Enterobacter B-14, a well-studied chlorpyrifos-degrading bacterial strain. Strain X1^T can tolerate high concentrations (500 mg/L) of chlorpyrifos over a wide range of temperatures (30–42 °C) and pH values (5–9). RT-qPCR analysis showed that the organophosphorus hydrolase (OpdB) in strain X1^T was an inducible enzyme, and the crude enzyme isolated in vitro could still maintain 75% degradation activity. Strain X1^T can simultaneously degrade chlorpyrifos and its main hydrolysate 3,5,6-trichloro-2-pyridinol. TCP could be further metabolized through stepwise oxidative dechlorination and further opening of the benzene ring to be completely degraded by the tricarboxylic acid cycle. The results provide a potential means for the remediation of chlorpyrifos- contaminated soil and water.

Identification and degradation characteristics of Bacillus cereus strain WD-2 isolated from prochloraz-manganese-contaminated soils

The bacterial strain WD-2, which was capable of efficiently degrading prochloraz-manganese, was isolated from soil contaminated with prochloraz-manganese, selected through enrichment culturing and identified as Bacillus cereus. Test results indicated that the optimal temperature and pH for bacterial growth were 35-40°C and 7.0-8.0, respectively. The highest degradation rate was above 88-90% when the pH was 7.0~8.0 and reached a maximum value (90.7%) at approximately 8.0. In addition, the bacterium showed the greatest growth ability with an OD600 of 0.805 and the highest degradation rate (68.2%) when glucose was chosen as the carbon source, while the difference in nitrogen source had no obvious influence on bacterial growth. The degradation rate exceeded 80% when the NaCl concentration was 0~2% and the rate reached 89.2% at 1%. When the concentration was higher than 7%, the growth of WD-2 and the degradation of prochloraz-manganese were found to be inhibited, and the degradation rate was merely 8.5%. The results indicated that strain WD-2 was able to effectively degrade prochloraz-manganese and might contribute to the bioremediation of contaminated soils.

A liquid chromatography with tandem mass spectrometry method to simultaneously determinate chlorpyrifos, imidacloprid and imidacloprid metabolites in wheat

A liquid chromatography with tandem mass spectrometry method was developed and validated to simultaneously determine chlorpyrifos, imidacloprid, and imidacloprid metabolites in soil, wheat grain, and wheat straw matrices. Satisfactory linearity (R² ≥ 0.9965) of the method was obtained for all analytes. The ranges of limits of detection and limits of quantification for seven analytes in three matrices were 0.17-66.7 and 0.5-200 μg/kg, respectively. Average recoveries were 72.85-81.25% for chlorpyrifos, 78.54-84.70% for imidacloprid, 73.83-81.03% for imidacloprid olefin, 71.47-80.61% for 5-hydroxy imidacloprid, 71.79-81.32% for imidacloprid urea, 70.42-82.20% for imidacloprid nitroguanidine, and 70.91-82.46% for imidacloprid 6-chloronicotinic acid in soil, wheat grain, and wheat straw. The intra- and interday relative standard deviations were less than 8%. The established method was successfully applied for the residual analysis of chlorpyrifos, imidacloprid, and imidacloprid metabolites in actual soil, wheat grain, and wheat straw samples. The results indicated that the established method could be used to detect trace amounts of chlorpyrifos, imidacloprid, and imidacloprid metabolites in wheat and that the method might be able to provide some data on the detection of these seven compounds in other crops.

Simultaneous biodegradation of bifenthrin and chlorpyrifos by Pseudomonas sp. CB2

The degradation of bifenthrin (BF) and chlorpyrifos (CP), either together or individually, by a bacterial strain (CB2) isolated from activated sludge was investigated. Strain CB2 was identified as belonging to genus Pseudomonas based on the morphological, physiological, and biochemical characteristics and a homological analysis of the 16S rDNA sequence. Strain CB2 has the potential to degrade BF and CP, either individually or in a mixture. The optimum conditions for mixture degradation were as follows: OD_600nm = 0.5; incubation temperature = 30°C; pH = 7.0; BF-CP mixture (10 mg L^-1 of each). Under these optimal conditions, the degradation rate constants (and half-lives) were 0.4308 d^-1 (1.61 d) and 0.3377 d^-1 (2.05 d) for individual BF and CP samples, respectively, and 0.3463 d^-1 (2.00 d) and 0.2931 d^-1 (2.36 d) for the BF-CP mixture. Major metabolites of BF and CP were 2-methyl-3-biphenylyl methanol and 3,5,6-trichloro-2-pyridinol, respectively. No metabolite bioaccumulation was observed. The ability of CB2 to efficiently degrade BF and CP, particularly in a mixture, may be useful in bioremediation efforts.

Isolation and Molecular Characterization of Novel Chlorpyrifos and 3,5,6-trichloro-2-pyridinol-degrading Bacteria from Sugarcane Farm Soils

Chlorpyrifos (CP) is one of the most widely used organophosphate pesticides in agriculture worldwide, but its extensive use has led to the contamination of various soil and water systems. Microbial bioremediation is considered to be one of the most viable options for the removal of CP from the environment; however, little is known about the soil bacterial diversity that degrade CP. Sequential soil and liquid culture enrichments enabled the isolation of bacterial CP degraders with sequence homologies to Xanthomonas sp., Pseudomonas sp., and Rhizobium sp. The efficacy of the three isolated strains: Xanthomonas sp. 4R3-M1, Pseudomonas sp. 4H1-M3, and Rhizobium sp. 4H1-M1 was further investigated for biodegradation of CP and its primary metabolic product, 3,5,6-trichloro-2-pyridinol (TCP). The results indicate that all three bacterial strains almost completely metabolized CP (10 mg/L) and TCP, occurring as a metabolic degradation product, in mineral salt media as a sole source of carbon and nitrogen. The isolated bacterial strains Xanthomonas sp. 4R3-M1 and Pseudomonas sp. 4H1-M3 could also degrade TCP (10 mg/L) as a sole carbon and nitrogen source, when provided externally. Thus, these bacterial strains may be effective in practical application of bioremediation of both CP and TCP.

Comparison of theoretical and experimental values for plant uptake of pesticide from soil

Pesticides that persist in soils may be taken up by the roots of plants. One way to assess plant uptake is to theoretically predict the extent of plant uptake using a mathematical model. In this study, a model was developed to predict plant uptake of pesticide residues in soils using various parameters, such as pesticide mobility within soil, plant transpiration stream, root-soil transfer rate, plant growth, and pesticide dissipation in either soils or plants. The accuracy of the model was evaluated by comparing the modeled concentrations with measured uptake concentrations of chlorpyrifos (CP) in lettuce, grown on treated soils with concentrations of approximately 10 and 20 mg kg-1 CP. Measured concentrations of CP in lettuce at 21, 30, and 40 d after planting were between the 5th and 95th percentiles of model variation. A high correlation coefficient of > 0.97 between modeled and measured concentrations was found. Coefficients of variation of mean factors to residual errors were between 25.3 and 48.2%. Overall, modeling results matched the experimental results well. Therefore, this plant uptake model could be used as an assessment tool to predict the extent of plant uptake of pesticide residues in soils.

Bio-Mineralization of Organophosphorous Insecticide-Chlorpyrifos and its Hydrolyzed Product 3,5,6-Trichloro-2-Pyridinol by Staphylococcus Sp. ES-2

Application of Chlorpyrifos on agricultural fields to protect crops against pests results in accumulation of it in soil and other environmental samples. The insecticide transform into 3,5,6-Trichloro-2-Pyridinol (TCP) through hydrolysis in soil, which has got antimicrobial property and hence resists its degradation in natural condition. In the current findings, a bacterial isolate capable of mineralizing Chlorpyrifos without accumulation of TCP was isolated from agricultural soil by enrichment method. Based on Morphological, Biochemical Characterization and with Bergey’s Manual comparision, the isolate was identified as Staphylococcus sp. The isolate was found to metabolize chlorpyrifos completely in Mineral salt medium with chlorpyrifos as the sole carbon source. No metabolites of chlorpyrifos were detected in Liquid Chromatography-Mass Spectroscopy (LC-MS) analysis after 7 days of incubation. The novelty of the outcome of the experiment relies on Staphylococcus sp.ES-2 in complete mineralization of chlorpyrifos which can be used as a potential bioaugmenting agent in the chlorpyrifos contaminated sites.

Biodegradation of Chlorpyrifos by Pseudomonas Resinovarans Strain AST2.2 Isolated from Enriched Cultures

A bacterial strain AST2.2 with chlorpyrifos degrading ability was isolated by enrichment technique from apple orchard soil with previous history of chlorpyrifos use. Based on the morphological, biochemical tests and 16S rRNA sequence analysis, AST2.2 strain was identified as Pseudomonas resinovarans. The strain AST2.2 utilized chlorpyrifos as the sole source of carbon and energy. This strain exhibited growth upto 400mg/l concentration of chlorpyrifos and exhibited high extracellular organophosphorus hydrolase (OPH) activity. Gas chromatography-flame ionization detector (GC-FID) studies revealed that Pseudomonas resinovarans AST2.2 degraded 43.90 % of chlorpyrifos (400 mg/l) within 96 hrs. Intermediates of chlorpyrifos degradation were identified using GC-MS. This strain have potential to degrade chlorpyrifos and thus can be used for bioremediation and ecological restoration of sites contaminated with chlorpyrifos

Binding and detoxification of chlorpyrifos by lactic acid bacteria on rice straw silage fermentation

This investigation examined the reduction of pesticide residues on straw inoculated with lactic acid bacteria (LAB) during ensiling. Lactobacillus casei WYS3 was isolated from rice straw that contained pesticide residues. Non-sterilized rice straw, which was inoculated with L. casei WYS3, showed increased removal of chlorpyrifos after ensiling, compared with rice straw that was not inoculated with L. casei WYS3 or sterilized rice straw. In pure culture, these strains can bind chlorpyrifos as indicated by high-performance liquid chromatography analysis. Viable L. casei WYS3 was shown to bind 33.3-42% of exogenously added chlorpyrifos. These results are similar to those of acid-treated cells but less than those of heat-treated cells, which were found to bind 32.0% and 77.2% of the added chlorpyrifos respectively. Furthermore, gas chromatography-mass spectrometry analysis determined that L. casei WYS3 detoxified chlorpyrifos via P-O-C cleavage. Real-time polymerized chain reaction analysis determined that organophosphorus hydrolase gene expression tripled after the addition of chlorpyrifos to LAB cultures, compared with the control group (without chlorpyrifos). This paper highlights the potential use of LAB starter cultures for the detoxification and removal of chlorpyrifos residues in the environment.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol using a novel bacterium Ochrobactrum sp. JAS2: A proposal of its metabolic pathway

Biodegradation of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were studied with a novel bacterial strain JAS2 isolated from paddy rhizosphere soil. The molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Ochrobactrum sp. JAS2. The JAS2 strain degraded 300mgl(-1) of chlorpyrifos within 12h of incubation in the aqueous medium and it produced the TCP metabolite. However, after 72h of incubation TCP was also completely degraded by the JAS2 strain. A tentative degradation pathway of chlorpyrifos by Ochrobactrum sp. JAS2 has been proposed on basis of GC-MS analysis. The complete degradation of chlorpyrifos occurred within 24h in the soil spiked with and without addition of nutrients inoculated with Ochrobactrum sp. JAS2. TCP was obtained in both the studies which was degraded completely by 96h in the soil spiked with nutrients and whereas 120h in absence of nutrients in the soil. The mpd gene which is responsible for organophosphorus hydrolase production was identified. The isolates Ochrobactrum sp. JAS2 also exhibited a time dependent increase in the amount of tricalcium phosphate solubilization in Pikovskaya's medium. Further screening of the strain JAS2 for auxiliary plant growth promoting activities revealed its remarkable capability of producing the indole acetic acid (IAA), hydrogen cyanide (HCN) and ammonia.

Interpretation and estimation for dynamic mobility of chlorpyrifos in soils containing different organic matters

The adsorption and removal behaviors of the organophosphate insecticide chlorpyrifos in two soils (AS and GW soils) with different organic matter contents were investigated to predict the dynamic residues in the soil environment. The adsorption test showed that the chlorpyrifos adsorptive power for the AS soil containing high organic matter content was greater than that for the GW soil. The extent of the time-dependent removal of chlorpyrifos in the tested soils was not significantly different except at 90 days after the treatment. The availability of a chemical-specific residue model developed in this study was statistically assessed to estimate the chlorpyrifos residue in soil solutions that could be absorbed into plants. The values modeled using the soil experimental data were satisfactory, having a mean deviation of 32% from the measured data. The correlation between the modeled and measured data was acceptable, with mean coefficients of correlation (R(2)) of 0.89. Furthermore, the average of the residual error was low at 0.43, which corresponded to a mean factor of -1.9. The developed model could be used as a critical tool to predict the subsequent plant uptake of chlorpyrifos.

Ecotoxicity of two organophosphate pesticides chlorpyrifos and dichlorvos on non-targeting cyanobacteria Microcystis wesenbergii

Organophosphate pesticides (OPs), as a replacement for the organochlorine pesticides, are generally considered non-toxic to plants and algae. Chlorpyrifos and dichlorvos are two OPs used for pest control all over the world. In this study, the dose-response of cyanobacteria Microcystis wesenbergii on OPs exposure and the stimulating effect of OPs with and without phosphorus source were investigated. The results showed that high concentrations of chlorpyrifos and dichlorvos caused significant decrease of chlorophyll a content. The median inhibitory concentrations (EC50) of chlorpyrifos and dichlorvos at 96 h were 15.40 and 261.16 μmol L(-1), respectively. Growth of M. wesenbergii under low concentration of OPs (ranged from 1/10,000 to 1/20 EC50), was increased by 35.85 % (chlorpyrifos) and 41.83 % (dichlorvos) at 120 h, respectively. Correspondingly, the highest enhancement on the maximum quantum yield (F v/F m) was 4.20 % (24 h) and 9.70 % (48 h), respectively. Chlorophyll fluorescence kinetics, known as O-J-I-P transients, showed significant enhancements in the O-J, J-I, and I-P transients under low concentrations of dichlorvos at 144 h, while enhancements of chlorophyll fluorescence kinetics induced by low concentrations of chlorpyrifos were only observed in the J-I transient at 144 h. Significant decreases of chlorophyll content, F v/F m and O-J-I-P transients with OPs as sole phosphorus source were found when they were compared with inorganic phosphate treatments. The results demonstrated an evidently hormetic dose-response of M. wesenbergii to both chlorpyrifos and dichlorvos, where high dose (far beyond environmental concentrations) exposure caused growth inhibition and low dose exposure induced enhancement on physiological processes. The stimulating effect of two OPs on growth of M. wesenbergii was negligible under phosphate limitation.

Biodegradation of polychlorinated biphenyls (PCBs) by the novel identified cyanobacterium Anabaena PD-1

Polychlorinated biphenyls (PCBs), a class of hazardous pollutants, are difficult to dissipate in the natural environment. In this study, a cyanobacterial strain Anabaena PD-1 showed good resistance against PCB congeners. Compared to a control group, chlorophyll a content decreased 3.7% and 11.7% when Anabaena PD-1 was exposed to 2 and 5 mg/L PCBs for 7 d. This cyanobacterial strain was capable of decomposing PCB congeners which was conclusively proved by determination of chloride ion concentrations in chlorine-free medium. After 7 d, the chloride ion concentrations in PCB-treated groups (1, 2, 5 mg/L) were 3.55, 3.05, and 2.25 mg/L, respectively. The genetic information of strain PD-1 was obtained through 16S rRNA sequencing analysis. The GenBank accession number of 16S rRNA of Anabaena PD-1 was KF201693.1. Phylogenetic tree analysis clearly indicated that Anabaena PD-1 belonged to the genus Anabaena. The degradation half-life of Aroclor 1254 by Anabaena PD-1 was 11.36 d; the total degradation rate for Aroclor 1254 was 84.4% after 25 d. Less chlorinated PCB congeners were more likely to be degraded by Anabaena PD-1 in comparison with highly chlorinated congeners. Meta- and para-chlorines in trichlorodiphenyls and tetrachlorobiphenyls were more susceptible to dechlorination than ortho-chlorines during the PCB-degradation process by Anabaena PD-1. Furthermore, Anabaena PD-1 can decompose dioxin-like PCBs. The percent biodegradation of 12 dioxin-like PCBs by strain PD-1 ranged from 37.4% to 68.4% after 25 days. Results above demonstrate that Anabaena PD-1 is a PCB-degrader with great potential for the in situ bioremediation of PCB-contaminated paddy soils.

Cyanobacteria: Photoautotrophic Microbial Factories for the Sustainable Synthesis of Industrial Products

Cyanobacteria are widely distributed Gram-negative bacteria with a long evolutionary history and the only prokaryotes that perform plant-like oxygenic photosynthesis. Cyanobacteria possess several advantages as hosts for biotechnological applications, including simple growth requirements, ease of genetic manipulation, and attractive platforms for carbon neutral production process. The use of photosynthetic cyanobacteria to directly convert carbon dioxide to biofuels is an emerging area of interest. Equipped with the ability to degrade environmental pollutants and remove heavy metals, cyanobacteria are promising tools for bioremediation and wastewater treatment. Cyanobacteria are characterized by the ability to produce a spectrum of bioactive compounds with antibacterial, antifungal, antiviral, and antialgal properties that are of pharmaceutical and agricultural significance. Several strains of cyanobacteria are also sources of high-value chemicals, for example, pigments, vitamins, and enzymes. Recent advances in biotechnological approaches have facilitated researches directed towards maximizing the production of desired products in cyanobacteria and realizing the potential of these bacteria for various industrial applications. In this review, the potential of cyanobacteria as sources of energy, bioactive compounds, high-value chemicals, and tools for aquatic bioremediation and recent progress in engineering cyanobacteria for these bioindustrial applications are discussed.

Chlorpyrifos degradation in soils with different treatment regimes within Nzoia River Drainage Basin, Kenya

Two organic amendments, filter mud compost and Tithonia diversifolia leaves generated within a sugarcane growing area were used to enhance the degradation of chlorpyrifos in soil. Filter mud compost and T. diversifolia leaves significantly enhanced degradation of chlorpyrifos in soils (p < 0.05) with DT50 values of 21 and 24 days, respectively. Furthermore, field degradation of chlorpyrifos in soil with prior exposure to chlorpyrifos was significantly enhanced (p = 0.034) with DT50 of 21 days compared to 30 days in soil with no previous exposure. Degradation of chlorpyrifos in sterile and non-sterile soils were significantly different (p = 0.023) with DT50 values of 161 and 27 days, respectively. Results show enhanced degradation of chlorpyrifos in organically amended soils and soils with prior exposure to the pesticide. These amendments show promise in a continuing effort to reduce chlorpyrifos concentrations in soils.

Isolation and characterization of a highly efficient chlorpyrifos degrading strain of Cupriavidus taiwanensis from sludge

In this study, a highly effective chlorpyrifos (CP)-degrading bacterium (termed strain X1) was isolated from the sludge of drain outlet of a chlorpyrifos manufacturer. Strain X1 was identified as Cupriavidus taiwanensis based upon the analysis of the 16S rDNA gene and biochemical characteristics, which is capable of transforming CP into 3,5,6-trichloro-2-pyridinol (TCP), and the resulting TCP was further metabolized when performed in an aqueous medium. Degradation experiments were carried out under different conditions at the range of pH (5.0∼9.0) and temperature (22∼42 °C), and the optimized pH and temperature were 7.0 and 32 °C respectively. Biotransformation of high concentration of CP was also determined; 400 mg l(À1) of CP was completely transformed within 36 h; approximately 95% of CP was removed within 48 h when concentration of CP was up to 500 mg l(À1) . A genomic library was successfully constructed to clone the gene encoding the CP hydrolase, and a positive transformant with clear hydrolytic zones was obtained and analyzed. The insert gene sequence exhibited close relationship with 99% similar to opdB gene encoding parathion hydrolase, whereas, transformant failed in degrading the accumulated TCP. These results highlight the potential of this bacterium to be used in the cleanup of CP.

Low and high doses of UV-B differentially modulate chlorpyrifos-induced alterations in nitrogen metabolism of cyanobacteria

The present study assessed the comparative responses on the specific growth rate, nitrogen metabolism and enzymes associated with nitrogen metabolism in two nitrogen fixing cyanobacteria-Nostoc muscorum and Phormidium foveolarum exposed to two UV-B doses (low; UV-BL: 0.5472kJm(-2) and high; UV-BH: 5.472kJm(-2)) and two doses of the insecticide chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate; low i.e. CPL, 1µgml(-1) and high i.e. CPH, 2µgml(-1)) singly and in combination. The specific growth rate, NO3(-) and NO2(-) uptake, nitrate assimilating enzymes - nitrate reductase and nitrite reductase and ammonium assimilating enzymes - glutamine synthetase and glutamate synthase were severely affected when treated either with CPH or/and UV-BH while glutamate dehydrogenase exhibited a stimulatory response. CPL also reduced all the measured parameters (except GDH activity) after 24h, however, a stimulatory effect was observed after 72h due to an increase in nitrogen metabolism (and other antioxidant) enzymes during this period. UV-BL did not cause significant alteration in the studied parameters while in combination with CP doses, it either alleviated the inhibitory effects or further enhanced the CPL induced activities of these enzymes (except GDH). Overall results indicate the resistant nature of P. foveolarum against the inhibitory doses of UV-B and chlorpyrifos in comparison to N. muscorum.

Biodegradation of chlorpyrifos by Pseudomonas sp. in a continuous packed bed bioreactor

Biodegradation of chlorpyrifos (CP) by Pseudomonas (Iso 1) sp. was investigated in batch as well as continuous bioreactors packed with polyurethane foam pieces. The optimum process parameters for the maximum removal of CP, determined through batch experiments, were found to be: inoculum level, 300×10(6)CfumL(-1); CP concentration, 500mgL(-1); pH 7.5; temperature, 37°C and DO, 5.5mgL(-1). The continuous packed bed bioreactor was operated at various flow rates (10-40mLh(-1)) under the optimum conditions. The steady state CP removal efficiency of more than 91% was observed up to the inlet load of 300mgL(-1)d(-1). The bioreactor was sensitive to flow fluctuations but was able to recover its performance quickly and exhibited the normal plug-flow behavior. Accumulation of TCP (3,5,6-trichloro-2-pyridinol) affected the reactor performance.

Kinetics of biotransformation of chlorpyrifos in aqueous and soil slurry environments

The attenuation of chlorpyrifos (CPF) by the enriched indigenous soil microorganism was studied in 15 d aerobic and 60 d anaerobic batch experiments in aqueous and soil slurry (1:3 w/w) media. At the end of the batch experiments, 2.78 ± 0.11 μM of CPF was degraded by 82% in aerobic and 66% in anaerobic aqueous environments, while 12.4 ± 0.5 μM of CPF was degraded by 48% in aerobic and 31% in anaerobic soil slurries. The reduced degradation in the soil slurries was due to the significantly (2-10 times) slower rate of degradation of soil phase CPF compared with its degradation rate in water. The pathways of degradation of CPF were identified, including a partial anaerobic degradation pathway that is constructed for the first time. The simulation of the various conversions in the degradation pathways using first order kinetics was used to analyze relative persistence of metabolites. The common metabolite 3,5,6-trichloro-2-pyridinol (TCP) accumulated (increased monotonically during the period of experiments) in aerobic soil slurry and in anaerobic aqueous as well as soil slurry systems but did not accumulate in aerobic aqueous system. The most toxic compound in the pathway, chlorpyrifos oxon (CPFO) was not detected in anaerobic environment. In aerobic environment, CPFO was short lived in aqueous medium, but accumulated slowly in the soils.

Evaluation of toxicological impact of cartap hydrochloride on some physiological activities of a non-heterocystous cyanobacterium Leptolyngbya foveolarum

The present study was aimed to the evaluation of toxicological impact of insecticide cartap hydrochloride on photosynthesis and nitrogen assimilation of a non-heterocystous cyanoprokaryote Leptolyngbya foveolarum isolated from paddy fields of Punjab, India. The microorganism tolerated commercial grade insecticide up to 80 ppm. Lower concentration (20 ppm) of cartap supported good growth with high dry weight of biomass, total protein content, photosynthetic pigments, photosynthesis and respiration compared to untreated control cultures while higher concentrations (40 and 60 ppm) inhibited these parameters in a dose dependent manner. Treatment of the microorganism with 60 ppm cartap lowered the content of photosynthetic pigments with maximum inhibitory effect on phycoerythrin (70% decrease) followed by allophycocyanin (66% decrease). Rates of photosynthesis and respiration were inhibited by 63% and 45%, respectively, while PS-I, II and whole chain activity were decreased by 45%, 67% and 40% respectively, compared to untreated control cultures. Cartap at 60 ppm decreased nitrate and nitrite uptake by 31% and 61%, respectively, whereas uptake of ammonium was slightly increased (18%) in cartap (60 ppm) treated cells. Nitrate and nitrite reductase, and glutamine synthetase activities of the microorganism decreased by 36-50% in 60 ppm cartap. The low levels of growth, photosynthetic pigments and activities of nitrogen assimilating enzymes in cells grown in nitrogen depleted medium supplement with insecticide indicated that insecticide may be used by the organism as a nitrogen source.

Isolation and characterization of a novel native Bacillus thuringiensis strain BRC-HZM2 capable of degrading chlorpyrifos

Studies were carried out to isolate chlorpyrifos degrading Bacillus thuringiensis (Bt) strains from chlorpyrifos-contaminated samples. Six Bt strains (isolation rate 2.7%) were isolated by modified sodium acetate antibiotic heat treatment, and one novel strain (BRC-HZM2) was selected for further analysis. Phenotype and phylogeny analysis of this strain was conducted on the basis of biochemical reactions, antibiotic sensitivity, 16s rRNA genes, plasmid profile, insecticidal crystal protein profiles, and PCR-RFLP for cry and cyt genes. The degradation rate of chlorpyrifos in liquid culture was estimated during 48 h of incubation for the isolate BRC-HZM2. More than 50% of the initial chlorpyrifos concentration degraded within 12 h, 88.9% after 48 h. These results highlight the potential of the Bt strain for biological control and the bioremediation of environments contaminated with chlorpyrifos.

Anilofos tolerance and its mineralization by the cyanobacterium Synechocystis sp. strain PUPCCC 64

This study deals with anilofos tolerance and its mineralization by the common rice field cyanobacterium Synechocystis sp. strain PUPCCC 64. The organism tolerated anilofos up to 25 mg L⁻¹. The herbicide caused inhibitory effects on photosynthetic pigments of the test organism in a dose-dependent manner. The organism exhibited 60, 89, 96, 85 and 79% decrease in chlorophyll a, carotenoids, phycocyanin, allophycocyanin and phycoerythrin, respectively, in 20 mg L⁻¹ anilofos on day six. Activities of superoxide dismutase, catalase and peroxidase increased by 1.04 to 1.80 times over control cultures in presence of 20 mg L⁻¹ anilofos. Glutathione content decreased by 26% while proline content was unaffected by 20 mg L⁻¹ anilofos. The test organism showed intracellular uptake and metabolized the herbicide. Uptake of herbicide by test organism was fast during initial six hours followed by slow uptake until 120 hours. The organism exhibited maximum anilofos removal at 100 mg protein L⁻¹, pH 8.0 and 30°C. Its growth in phosphate deficient basal medium in the presence of anilofos (2.5 mg L⁻¹) indicated that herbicide was used by the strain PUPCCC 64 as a source of phosphate.

Biodegradation of chlorpyrifos and 3,5,6-trichloro-2-pyridinol by Cupriavidus sp. DT-1

A bacterial strain, Cupriavidus sp. DT-1, capable of degrading chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) and using these compounds as sole carbon source was isolated and characterized. Investigation of the degradation pathway showed that chlorpyrifos was first hydrolyzed to TCP, successively dechlorinated to 2-pyridinol, and then subjected to the cleavage of the pyridine ring and further degradation. The mpd gene, encoding the enzyme responsible for chlorpyrifos hydrolysis to TCP, was cloned and expressed in Escherichia coli BL21. Inoculation of chlorpyrifos-contaminated soil with strain DT-1 resulted in a degradation rate of chlorpyrifos and TCP of 100% and 94.3%, respectively as compared to a rate of 28.2% and 19.9% in uninoculated soil. This finding suggests that strain DT-1 has potential for use in bioremediation of chlorpyrifos-contaminated environments.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol by a new fungal strain Cladosporium cladosporioides Hu-01

Intensive use of chlorpyrifos has resulted in its ubiquitous presence as a contaminant in surface streams and soils. It is thus critically essential to develop bioremediation methods to degrade and eliminate this pollutant from environments. We present here that a new fungal strain Hu-01 with high chlorpyrifos-degradation activity was isolated and identified as Cladosporium cladosporioides based on the morphology and 5.8S rDNA gene analysis. Strain Hu-01 utilized 50 mg·L⁻¹ of chlorpyrifos as the sole carbon of source, and tolerated high concentration of chlorpyrifos up to 500 mg·L⁻¹. The optimum degradation conditions were determined to be 26.8°C and pH 6.5 based on the response surface methodology (RSM). Under these conditions, strain Hu-01 completely metabolized the supplemented chlorpyrifos (50 mg·L⁻¹) within 5 d. During the biodegradation process, transient accumulation of 3,5,6-trichloro-2-pyridinol (TCP) was observed. However, this intermediate product did not accumulate in the medium and disappeared quickly. No persistent accumulative metabolite was detected by gas chromatopraphy-mass spectrometry (GC-MS) analysis at the end of experiment. Furthermore, degradation kinetics of chlorpyrifos and TCP followed the first-order model. Compared to the non-inoculated controls, the half-lives (t_1/2) of chlorpyrifos and TCP significantly reduced by 688.0 and 986.9 h with the inoculum, respectively. The isolate harbors the metabolic pathway for the complete detoxification of chlorpyrifos and its hydrolysis product TCP, thus suggesting the fungus may be a promising candidate for bioremediation of chlorpyrifos-contaminated water, soil or crop.

Compatibility of ascorbate-glutathione cycle enzymes in cyanobacteria against low and high UV-B exposures, simultaneously exposed to low and high doses of chlorpyrifos

This study deals with the comparative responses of the two cyanobacteria viz. Nostoc muscorum and Phormidium foveolarum against single and combined doses of low (UV-B(L,) 0.1 μmol m(-2) s(-1)) and high (UV-B(H), 1.0 μmol m(-2) s(-1)) fluence rates of ultraviolet-B radiation with low (CP(L), 1 μg ml(-1)) and high (CP(H), 2 μg ml(-1)) doses of the insecticide chlorpyrifos by measuring changes in growth, ascorbate-glutathione cycle enzymes and related metabolites. CP(L) and UV-B(L) both caused lesser increase in ROS but significantly stimulated AsA-GSH cycle enzymes. On the other hand, CP(H) and UV-B(H) posed inhibitory effects by enhancing ROS and inhibiting AsA-GSH cycle enzymes. Inhibitions in CP(H) or UV-B(H) treated samples were significantly prevented when they were supplemented with UV-B(L) and CP(L) (after 72 h), respectively by lowering down ROS and enhancing AsA-GSH enzymes and related metabolites which manifested in terms of improved biomass accumulation.