Copper Nanoparticles in Agriculture: Biological Synthesis and Antimicrobial Activity

Copper is an essential micronutrient incorporated into many proteins and metalloenzymes, and plays a significant role in the health and nutrition of plants. Copper nanoparticles due to unique properties are more efficient than bulk copper particles in activity and functioning. Due to antimicrobial activity copper nanoparticles are finding new applications in agriculture, healthcare and industry. However there are growing concerns regarding the indiscriminate use of either copper or copper nanoparticles which can cause toxic effects to plants and other living organisms. We review here the biological synthesis of copper nanoparticle using plant extracts and microorganisms; antibacterial and antifungal activity of copper nanoparticles and the impact of copper nanoparticles on crops and pathogenic microorganisms. Copper nanoparticles of various sizes ranging from 5 to 280 nm have been synthesized by using extracts prepared from Syzygium aromaticum, Tabernaemontana divaricate, Vitis vinifera, Aloe vera, Cassia alata, Centella asitica, Bifurcaria bifurcate, Gloriosa superba and Citrus medica. Biosynthesis of small spherical copper oxide nanoparticles ranging from 5 to 10 nm or with average size of 15 nm have been achieved by using leaf extract or latex produced by plants. Copper nanoparticles ranging from 5 to 295 nm have also been synthesized by using microorganisms both bacteria and fungi. Comparisons of microbial synthesized copper nanoparticles with those synthesized using plant extracts have shown that those synthesized by microorganisms had smaller dimension. Copper nanoparticles ranging in size from 5 to 50 nm were synthesized in about 80 % sample of microorganisms and about 70 % samples of plant extracts screened for synthesis. Biologically-synthesized copper nanoparticles show good antibacterial and antifungal activity inhibiting the growth of pathogenic bacteria belonging to Gram positive and Gram negative genera, and plant pathogenic fungi. Growth inhibition has been seen in case Staphylococcus aureus, Enterococcus faecalis, Propionibacterium acnes, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Shigella flexneri, Proteus vulgaris and Salmonella typhimurium. Antifungal activity of copper nanoparticles against the pathogenic fungi Fusarium culmorum, Fusarium oxysporum, Fusarium graminearum and Phytophthora infestans has also been recorded. Copper nanoparticles at concentrations below 100 ppm have been reported to enhance germination and growth of some plants.