Chlorpyrifos degradation by the cyanobacterium Synechocystis sp. strain PUPCCC 64

Background, aim, and scope Indiscriminate use of insecticides leads to environmental problems and poses a great threat to beneficial microorganisms. The aim of the present work was to study chlorpyrifos degradation by a rice field cyanobacterium Synechocystis sp. strain PUPCCC 64 so that the organism is able to reduce insecticide pollution in situ. Material and methods The unicellular cyanobacterium isolated and purified from a rice field was identified by partial 16S rRNA gene sequence as Synechocystis sp. strain PUPCCC 64. Tolerance limit of the organism was determined by studying its growth in graded concentrations (2.5– 20 mg/L) of chlorpyrifos. Chlorpyrifos removal was studied by its depletion from the insecticide supplemented growth medium, and its biodegradation products were identified in the cell extract, biomass wash, and growth medium. Results and discussion The organism tolerated chlorpyrifos up to 15 mg/L.Major fraction of chlorpyrifos was removed by the organism during the first day followed by slow uptake. Biomass, pH, and temperature influenced the insecticide removal and the organism exhibited maximum chlorpyrifos removal at 100 mg protein/L biomass, pH 7.0, and 30°C. The cyanobacteriummetabolized chlorpyrifos producing a number of degradation products as evidenced by GC-MS chromatogram. One of the degradation products was identified as 3,5,6- trichloro-2-pyridinol. Conclusion and recommendations Present study reports the biodegradation of chlorpyrifos by Synechocystis sp. Biodegradation of the insecticide by the cyanobacterium is significant as it can be biologically removed from the environment. The cyanobacterium may be used for bioremediation of chlorpyrifos-contaminated soils

The prescribed time sliding mode control for attitude tracking of spacecraft

With the development of the space missions, there are extensive missions in the demand of the prescribed time convergence. However, it's still a difficult work to combine the prescribed time method with the sliding mode control due to the infinite gain of the prescribed time method while approaching the prescribed time and two periods of sliding mode control. In this paper, a new prescribed time sliding mode control method is proposed for general systems with matched disturbances, from the second-order system to the high-order system. A novel sliding mode variable with explicit time term is designed for achieving the prescribed time convergence. More importantly, as time approaches the prescribed time, the singularity of control input can be avoided. Finally, this paper presents a disturbance observer-based prescribed time sliding mode control method for attitude tracking of spacecraft, and the efficiency of this method has been verified through the numerical simulations