Lakshmi Tewari

Transmission electron microscopic study of the cytological changes in Sclerotium rolfsii parasitized by a biocontrol fungus Trichoderma sp

There is a recent trend towards the use of eco-friendly biological control agents for protecting crops from pest and disease, especially soil-borne plant pathogens, as an alternative to existing chemical methods. Among various biocontrol agents, Trichoderma, which has multiple mechanisms for the biocontrol of phytopathogens, is used widely. The present study explores the role of Trichoderma sp. in inducing cytological changes in fungal plant pathogens during parasitization. In dual culture plates, all the fungal isolates (SE6, KT6, KT28, and BRT11) along with a standard culture of T. harzianum were able to antagonize and mycoparasitize two soil-borne fungal phytopathogens (Sclerotium rolfsii and Rhizoctonia solani) of chickpea wilt complex. The suppression of S. rolfsii was slower than that of R. solani. The interaction between T. harzianum and sclerotia of S. rolfsii was studied by light microscopy and transmission electron microscopy (TEM). Ultra-structural examinations revealed that growth and development of Trichoderma resulted in extensive host cell alterations, such as retraction, aggregation and disintegration of cytoplasmic contents. Lysis and deformation of hyphal cell wall, degradation and disappearance of cytoplasmic contents and loss of cellular integrity in sclerotia of S. rolfsii paratisized by T. harzianum is clearly apparent from transmission electron micrographs.

Lignolytic mushroom Lenzites elegans WDP2: Laccase production, characterization, and bioremediation of synthetic dyes

A mycoremedial study was undertaken for decolourization of synthetic dyes using wood rot fungal culture Lenzites elegans WDP2. The culture was isolated from decaying wood as fruiting body, and identified on the basis of 5.8S ITS rRNA gene sequence analysis. Qualitative plate screening of culture showed extracellular laccase and lignin peroxidase production, while only laccase enzyme was produced in higher amount (156.793 Uml-1) in minimal salt broth medium containing glucose and veratryl alcohol. Laccase activity was increased up to 189.25 Uml-1 after optimization of laccase production by optimization of one variable at a time approach. Molecular characterization of laccase enzyme was done using SDS PAGE and Native PAGE based isozyme analyses. The culture was able to decolorize three synthetic dying compounds (congo red, Malachite green and brilliant green) in broth media, while showed very less decolourization in plate assay. The fungal culture varied in their dye decolourizing potential in broth culture, showing 92.77%, 21.27% and 98.8% maximum decolourization of brilliant green, malachite green and congo red respectively. The congo red dye was completely bio-absorbed by fungal culture within one month. The fungal decolourized broth also revealed the extracellular laccase activity; varied from 10 Uml-1 to 68.5 Uml-1 in all the three cases, supports the involvement of laccase enzyme in decolorization. Phase contrast microscopy clearly revealed bio-sorption of the dyes by fungal culture into the mycelium/spores in the photomicrographs.

Phytostimulating Mechanisms and Bioactive Molecules of Trichoderma Species: Current Status and Future Prospects

Ever-increasing pressure on the agricultural land due to various biotic and abiotic stresses made agriculture a nonprofitable venture. In order to bring back the lost glory to agriculture, there is an urgent need to reclaim this eroded agriculture with sustainable practices, one among them is the use of plant growth-promoting microorganisms such as rhizosphere-competent Trichoderma sp. In this chapter, the major mechanisms and bioactive molecules involved in plant growth promotory activity of Trichoderma sp. are described in detail. Trichoderma sp. is also known to produce growth-regulating phytohormones and other bioactive molecules which are known to protect them against antimicrobial compounds secreted by plant, but they also help the plants in overcoming various stresses. Various hydrolytic enzymes such as chitinases, glucanases, and proteinases are produced by Trichoderma which aid in its mycoparasitic response. The fungus is also able to enhance plant growth through nutrient solubilization and its uptake. It mobilizes phosphates from fixed organic/inorganic phosphorus sources through both enzymatic (phosphatases, phytases) and nonenzymatic mechanisms (production of organic acids and siderophores). Trichoderma produces a wide array of secondary metabolites and volatile compounds which are mainly responsible for its biocontrol action. Suppression of fungal plant pathogens through mycoparasitism involves signal transduction and G protein signaling in Trichoderma. Secondary metabolites and volatile compounds produced by this fungus are very diverse in their occurrence and mode of action against phytopathogens. Recent developments in molecular biology, metabolomics, and proteomics have opened an insight for the use of secondary metabolites as biopesticides rather than the application of whole organisms.

Green Synthesis and Characterization of Iron Oxide Nanoparticles using Wrightia tinctoria Leaf Extract and their Antibacterial Studies

The synthesis of nanoparticles has become a matter of great interest in recent times due to their various advantageous properties and applications in a variety of fields. Recently, the exploitation of different plant materials for the biosynthesis of nanoparticles is considered a green technology because it does not involve any harmful chemicals. Among them, Iron nanoparticles (Fe NPs) are gaining importance for their use in environmental remediation technologies. In the present study, iron oxide nanoparticles (Fe3O4-NPs) were synthesized using a rapid, single step and completely green biosynthetic method by reduction of ferric chloride solution with Wrightia tinctoria leaf extract which acts as reducing agent and efficient stabilizer at room temperature. Synthesized nanoparticles were characterized using UV-visible spectrophotometer FT-IR, X-ray diffraction and SEM methods. The morphology of the nanoparticles mostly appeared to be porous and spongy, nanoclusters with panoramic view and range from 105-145 nm in size. X-ray diffraction showed that the nanoparticles are crystalline in nature, with a cubic shape and rhombohedral geometry. The synthesized Iron oxide nanoparticles exhibited potent antibacterial activity against gram positive and moderate activity against gram negative bacterial strains tested. Novelty of this present study is that the plant extract is very cost effective and eco friendly and thus can be economic and effective alternative for the large scale synthesis of iron oxide nanoparticles.