Sustainable supply of food and energy without posing any threat to environment is the current demand of our society in view of continuous increase in global human population and depletion of natural resources of energy. Cyanobacteria have recently emerged as potential candidates who can fulfill abovementioned needs due to their ability to efficiently harvest solar energy and convert it into biomass by simple utilization of CO 2 , water and nutrients. During conversion of radiant energy into chemical energy, these biological systems produce oxygen as a by-product. Cyanobacterial biomass can be used for the production of food, energy, biofertilizers, secondary metabolites of nutritional, cosmetics, and medicinal importance. Therefore, cyanobacterial farming is proposed as environment friendly sustainable agricultural practice which can produce biomass of very high value. Additionally, cyanobacterial farming helps in decreasing the level of greenhouse gas, i.e., CO 2 , and it can be also used for removing various contaminants from wastewater and soil. However, utilization of cyanobacteria for resolving the abovementioned problems is subjected to economic viability. In this review, we provide details on different aspects of cyanobacterial system that can help in developing sustainable agricultural practices. We also describe different large-scale cultivation systems for cyanobacterial farming and discuss their merits and demerits in terms of economic profitability.

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In the present study we have made an attempt to develop an eco-friendly, cheap and convenient biological (green) method for the synthesis of silver nanoparticles (AgNPs) using the cell extract of the cyanobacterium Nostoc sp. strain HKAR-2. Their anticancerous, antifungal and antibacterial properties were also studied against MCF-7 cells, two fungal strains (Aspergillus niger and Trichoderma harzianum) and two plant bacterial strains (Ralstonia solanacearum and Xanthomonas campestris), respectively. The structural, morphological and optical properties of green synthesized AgNPs were determined by UV-VIS spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, transmission electron microscopy selected area electron diffraction (TEM-SAED) and scanning electron microscopy (SEM). Spectroscopic analysis showed the peak at 419 nm due to the reduction of AgNO3 into silver ion by cyanobacterial extract indicating surface plasmon resonance (SPR) of the synthesized AgNPs. The XRD pattern of AgNPs showed the characteristic Bragg peaks at (111), ( 200), ( 220) and (311) facets of the face centre cubic (fcc) confirming their crystalline nature. FTIR analysis revealed that proteins and amino acids are responsible for the reduction of AgNO3 into Ag + as well as for the stability of nanoparticles. Zeta potential confirmed that the charge on the nanoparticles is 1.80 mV which indicates the presence of stable nanoparticles. The results of SEM and TEM confirmed the large agglomerated shape of AgNPs with size ranging between 51-100 nm. The AgNPs showed a dose-dependent cytotoxic activity against human breast cancer MCF-7 cells with IC50 of 27.5 µg/ml. They also exhibited excellent antibacterial and antifungal activities.

Reactive oxygen species (ROS) are cell signaling molecules synthesized inside the cells as a response to routine metabolic processes. In stress conditions such as ultraviolet radiation (UVR), ROS concentration increases several folds in the cells that become toxic for the cell survival. Here we present the method for in vivo detection of ROS by using an oxidant-sensing probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in cyanobacteria. This method provides reliable, simple, rapid and cost effective means for detection of ROS in cyanobacteria.