Microbial degradation of organophosphate pesticides: a review.

Biodegradation and bioremediation potential of diazinon-degrading Serratia marcescens to remove other organophosphorus pesticides from soils.

Performance evaluation of Malathion biodegradation in batch and continuous packed bed bioreactor (PBBR).

We report here the degradation of a pesticide, malathion, by Brevibacillus sp. strain KB2 and Bacillus cereus strain PU, isolated from soil samples collected from malathion contaminated field and an army firing range respectively. Both the strains were cultured in the presence of malathion under aerobic and energy-limiting conditions. Both strains grew well in the medium having malathion concentration up to 0.15%. Reverse phase HPLC–UV analysis indicated that Strain KB2 was able to degrade 72.20% of malaoxon (an analogue of malathion) and 36.22% of malathion, while strain PU degraded 87.40% of malaoxon and 49.31% of malathion, after 7 days of incubation. The metabolites mal-monocarboxylic acid and mal-dicarboxylic acid were identified by Gas chromatography/mass spectrometry. The factors affecting biodegradation efficiency were investigated and effect of malathion concentration on degradation rate was also determined. The strain was analyzed for carboxylesterase activity and maximum activity 210 ± 2.5 U ml−1 and 270 U ± 2.7 ml−1 was observed for strains KB2 and PU, respectively. Cloning and sequencing of putative malathion degrading carboxylesterase gene was done using primers based PCR approach.

Biodegradation of malathion by Brevibacillus sp. strain KB2 and Bacillus cereus strain PU

Microbial lipolytic enzymes – promising energy-efficient biocatalysts in bioremediation

Five malathion-degrading bacterial strains were enriched and isolated from soil samples collected from different agricultural sites in Cairo, Egypt. Malathion was used as a sole source of carbon (50 mg/l) to enumerate malathion degraders, which were designated as IS1, IS2, IS3, IS4, and IS5. They were identified, based on their morphological and biochemical characteristics, as Pseudomonas sp., Pseudomonas putida, Micrococcus lylae, Pseudomonas aureofaciens, and Acetobacter liquefaciens, respectively. IS1 and IS2, which showed the highest degrading activity, were selected for further identification by partial sequence analysis of their 16S rRNA genes. The 16S rRNA gene of IS1 shared 99% similarity with that of Alphaprotoebacterium BAL284, while IS2 scored 100% similarity with that of Pseudomonas putida 32zhy. Malathion residues almost completely disappeared within 6 days of incubation in IS2 liquid cultures. LC/ESI-MS analysis confirmed the degradation of malathion to malathion monocarboxylic and dicarboxylic acids, which formed as a result of carboxylesterase activity. A carboxylesterase gene (CE) was amplified from the IS2 genome by using specifically designed PCR primers. The sequence analysis showed a significant similarity to a known CE gene in different Pseudomonas sp. We report here the isolation of a new malathion-degrading bacteria from soils in Egypt that may be very well adapted to the climatic and environmental conditions of the country. We also report the partial cloning of a new CE gene. Due to their high biodegradation activity, the bacteria isolated from this work merit further study as potential biological agents for the remediation of soil, water, or crops contaminated with the pesticide malathion.

Screening for and isolation and identification of malathion-degrading bacteria: cloning and sequencing a gene that potentially encodes the malathion-degrading enzyme, carboxylestrase in soil bacteria.

The purpose of this study was to prepare a stable oil -in-water emulsion formulation of deltamethrin. Oil -in-water emulsion was prepared by using a two -step procedure. Stability studies were performed at different accelerated conditions (0∞C and 54∞C) to predict the stability of the formulation. Different parameters, namely, active ingre dient content, mean particle size distribution, pH, viscosity, flash point, effect of centrifugation, persistent foaming and emulsion stability were determined during stability studies. The formulation exhibited good stability after preparation at differen t temperatures. No phase separation was observed during stability testing.

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Preparation and characterization of alternative oil-in-water emulsion formulation of deltamethrin.

This study was designed to investigate the effect of hydrophilic-lipophilic balance (HLB) values of different surfactant mixtures on the physicochemical properties of emulsifiable concentrate formulations of difenoconazole. Physical tests of emulsion characteristics and storage stability studies were performed for the different samples to predict the stability of these formulations. Different parameters such as active ingredient content, pH, refractive index, surface tension, viscosity, flash point, persistent foam was determined for the prepared samples. The results showed that difenoconazole could be formulated as a stable emulsifiable concentrate by using a mixture of surfactants at HLB values 9.7, 11.9, 12.5 and 13.1. The storage stability test showed that the decomposition rate of the active ingredient content of difenoconazole in different stable formulations was within the acceptable limits of FAO Specifications. The physical and chemical properties of the stable formulations fulfilled the requirements of EC formulation. Original Research Article El-Sayed and Mohammad; JALSI, 22(4): 1-10, 2019; Article no.JALSI.44186 2

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Effect of Hydrophilic-Lipophilic Balance (HLB) Values of Surfactant Mixtures on the Physicochemical Properties of Emulsifiable Concentrate Formulations of Difenoconazole

Flonicamid and imidacloprid are insecticides that are commonly used for the protection of many annual open field crops, such as beans, against insects. Residues of these insecticides in the consumable product above the acceptable limits can cause health concerns or trade barriers; thus, the dissipation behaviour and the consumer risk assessment of flonicamid and imidacloprid residues in open field green beans were investigated. The initial concentrations were found to be 0.44 and 0.99 mg kg−1. The decline of residues followed in both cases the first-order kinetics model with half-lives of 2.3 (r2 0.912) and 2.1 (r2 0.977) days, for flonicamid and imidacloprid, respectively, while degraded almost completely after 14 days if applied according to the authorised patterns. The dietary risk assessment performed using the hazard quotient (RQ) and the EFSA PRIMo model showed no concern to consumer health with exposure values <2% of the acceptable daily intake (ADI) and <22% of the acute reference dose (ARfD) of each compound. In conclusion, the investigation of the dissipation behaviour of these compounds in green bean provides useful information to ensure safe pre-harvest intervals, acceptable dietary exposure and compliance with good agricultural practices and maximum residue levels. 

Walaa El-Sayed

Papers

Screening for and isolation and identification of malathion-degrading bacteria: cloning and sequencing a gene that potentially encodes the malathion-degrading enzyme, carboxylestrase in soil bacteria.

Preparation and characterization of alternative oil-in-water emulsion formulation of deltamethrin.

Effect of Hydrophilic-Lipophilic Balance (HLB) Values of Surfactant Mixtures on the Physicochemical Properties of Emulsifiable Concentrate Formulations of Difenoconazole

Investigation of the dissipation behaviour and exposure of flonicamid and imidacloprid in open field green beans under dry climatic conditions