Poonam C. Singh

Trichoderma: a potential bioremediator for environmental clean up

Environmental awareness has resulted in development of regulatory measures that aim to straighten past mistakes and protect the environment from future contamination and exploitation. However, much consideration and research needs to go into the decision-making process for an effective clean up of a particular contaminated site. Each technology developed has its advantages and limitations for the treatment of specific contaminants. Bioremediation and phytoremediation in association with microbes are innovative technologies having a potential to alleviate numerous environmental pollution problems. Owing to its dominant presence in contaminated sites, the application of the fungi in bioremediation is well documented. The genus Trichoderma is genetically very diverse with a number of capabilities among different strains with agricultural and industrial significance. It is also tolerant to a range of recalcitrant pollutants including heavy metals, pesticides, and polyaromatic hydrocarbons. This review presents an updated overview of application of Trichoderma for biological or phytobial remediation of environmental contaminants.

Trichoderma inoculation ameliorates arsenic induced phytotoxic changes in gene expression and stem anatomy of chickpea (Cicer arietinum)

Arsenic, a carcinogenic metalloid severely affects plant growth in contaminated areas. Present study shows role of Trichoderma reesei NBRI 0716 (NBRI 0716) in ameliorating arsenic (As) stress on chickpea under greenhouse conditions. Arsenic stress adversely affected seed germination (25%), chlorophyll content (44%) and almost eliminated nodule formation that were significantly restored on NBRI 0716 inoculation. It also restored stem anomalies like reduced trichome turgidity and density, deformation in collenchymatous and sclerenchymatous cells induced by As stress. Semi-quantitative RT-PCR of stress responsive genes showed differential expression of genes involved in synthesis of cell wall degrading enzymes, dormancy termination and abiotic stress. Upregulation of drought responsive genes (DRE, EREBP, T6PS, MIPS, and PGIP), enhanced proline content and shrunken cortex cells in the presence of As suggests that it creates water deficiency in plants and these responses were modulated by NBRI 0716 which provides a protective role. NBRI0716 mediated production of As reductase enzyme in chickpea and thus contributed in As metabolism. The study suggests a multifarious role of NBRI0716 in mediating stress tolerance in chickpea towards As.

High and low nodulation in relation to molecular diversity of chickpea mesorhizobia in Indian soils

Chickpea (Cicer arietinum L.) nodulation variants of two cultivars ICC 4948 and ICC 5003 were used as trap plants to isolate 385 native rhizobia from CCS Haryana Agricultural University, Hisar farm soil. After authentication and considering growth characteristics, selected 110 rhizobia revealed immense molecular diversity using the profiles of DNA fragments generated by Polymerase chain reaction (PCR) with enterobacterial repetitive intergeneric consensus (ERIC) sequences. Low nodulating variants of cvs ICC 4948 and ICC 5003 were able to trap more numbers of rhizobial genotypes, namely seven as compared four to five by high nodulating variants of these cultivars. Overall eight rhizobial genotypes were trapped by the chickpea cultivars. Rhizobial isolates from same nodule or same plants were present in the same or different clusters and few isolates showed 100% similarity also. Based on nodules from a plant, nodulation variant or cultivar, rhizobia could not be differentiated and no exclusive cluster was formed by either rhizobial isolates from low or high nodulating variants of both the cultivars. Two most efficient rhizobial isolates LN 707b and LN 7007 were characterized by amplification and sequencing of 16S rRNA gene. Rhizobial isolate LN 707b showed more than 98% similarity with Mesorhizobium sp SH 2851 and Mesorhizobium mediterraneum. Another isolate LN 7007 showed more than 99% similarity with the sequence of 16S r RNA gene of Mesorhizobium sp STM 398, and M. mediterraneum. So the chickpea rhizobia from Northern Indian subcontinent are proposed to be kept under M. mediterraneum strain LN707b and LN 7007.

Trichoderma inoculation augments grain amino acids and mineral nutrients by modulating arsenic speciation and accumulation in chickpea (Cicer arietinum L.).

Trichoderma reesei is an industrially important fungi which also imparts stress tolerance and plant growth promotion in various crops. Arsenic (As) contamination of field soils is one of the challenging problems in agriculture, posing potential threats for both human health and the environment. Plants in association with microbes are a liable method to improve metal tolerance and enhance crop productivity. Chickpea (Cicer arietinum L.), is an important grain legume providing cheap source of protein in semi-arid regions including As affected areas. In this study we report the role of T. reesei NBRI 0716 (NBRI 0716) in supporting chickpea growth and improving soil quality in As simulated conditions. NBRI 0716 modulated the As speciation and its availability to improve grain yield and quality (amino acids and mineral content) in chickpea (C. arietinum L.) plants grown in As spiked soil (100 mg As kg(-1) soil). Arsenic accumulation and speciation results indicate that arsenate [As(V)] was the dominant species in chickpea seeds and rhizosphere soil. The Trichoderma reduced total grain inorganic As (Asi) by 66% and enhanced dimethylarsonic acid (DMA) and monomethylarsinic acid (MMA) content of seed and rhizosphere soil. The results indicate a probable role of NBRI 0716 in As methylation as the possible mechanism for maneuvering As stress in chickpea. Analysis of functional diversity using carbon source utilization (Biolog) showed significant difference in diversity and evenness indices among the soil microbial rhizosphere communities. Microbial diversity loss caused by As were prevented in the presence of Trichoderma NBRI 0716.

Biological Control of Fusarium sp. NBRI-PMSF12 Pathogenic to Cultivated Betelvine by Bacillus sp. NBRI-W9, a Potential Biological Control Agent

Betelvine is prone to several fungal diseases including leaf spots, foot and root rot caused by Fusarium spp. due to humid conditions prevailing in fields. In the present study, a potent antagonistic bacterial endophyte and a virulent fungal pathogen were selected after rigorous screening of isolates from different betelvine varieties to provide an efficient biocontrol strategy in cultivation of betelvine. Wild varieties of crops are a rich source of untapped endophytes. Of the four betelvine varieties used for isolations and screening, the wild variety was richest in endophytic populations. Using 16S rRNA sequencing, the selected antagonist was identified as Bacillus sp. (NBRI-W9). The pathogen, virulent against cultivated varieties, was identified as Fusarium sp. (NBRI-PMSF12) using ITS 1 and 2 region sequencing. Under in vitro and field conditions, NBRI-W9 was able to induce early rooting, provide plant growth promotion, increase leaf size and yield (leaf number) and provide biocontrol against the Fusarium sp. infection. NBRI-W9 treatments showed bacterial colonization on the leaf surface preferably in the vicinity of pearl glands and the collenchyma region in scanning electron microscope (SEM) studies. NBRI-W9 was observed to directly enter the leaf by degrading cell walls and colonize the subcellular layers. SEM analysis showed direct confrontation of NBRI-W9 with Fusarium on the leaf surface and in the collenchyma region as one of the probable modes of biocontrol.

Chlorella vulgaris and Pseudomonas putida interaction modulates phosphate trafficking for reduced arsenic uptake in rice (Oryza sativa L.)

Rice grown in arsenic (As) contaminated areas contributes to high dietary exposure of As inducing multiple adverse effects on human health. The As contamination and application of phosphate fertilizers during seedling stage creates a high P and As stress condition. The flooded paddy fields are also conducive for algal growth and microbial activity. The present study proposes potential role of microalgae, Chlorella vulgaris (CHL) and bacteria, Pseudomonas putida (RAR) on rice plant grown under excess As and phosphate (P) conditions. The results show synchronized interaction of CHL + RAR which, reduces As uptake through enhanced P:As and reduced As:biomass ratio by modulating P trafficking. Gene expression analysis of different phosphate transporters exhibited correlation with reduced As uptake and other essential metals. The balancing of reactive oxygen species (ROS), proline accumulation, hormone modulation, and As sequestration in microbial biomass were elucidated as possible mechanisms of As detoxification. The study concludes that RAR and CHL combination mitigates the As stress during P-enriched conditions in rice by: (i) reducing As availability, (ii) modulating the As uptake, and (iii) improving detoxification mechanism of the plant. The study will be important in assessing the role and applicability of P solubilizing biofertilizers in these conditions.

Mycoremediation Mechanisms for Heavy Metal Resistance/Tolerance in Plants

Environmental pollution is an ever-increasing problem being faced by the world in the present era. Soil pollution is increasing, owing to dumping of all kinds of wastes, mining and using of agrochemicals and other anthropogenic activities. These pollutants include many recalcitrant organic compounds, e-wastes, isotopic wastes and heavy metals. Heavy metals are essentially polluting agricultural fields and thus affect productivity and quality of the produce. Accumulation of these toxic metals in plants leads to their subsequent transfer and biomagnification in the food chain. Therefore, their toxicity is an area of concern for ecological, evolutionary, nutritional and environmental reasons. Several strategies are being employed for remediation of agricultural soils, mycoremediation being one of them. Mycoremediation is an eco-friendly ‘green-clean’ technology that has tremendous potential to be utilized in the cleaning up of heavy metals and organic pollutants. Association of plant and fungi can detoxify toxic metals, translocate and accumulate them in the above-ground biomass, which has to be then harvested for metal recovery. Despite tremendous potential for the application of mycoremediation in the cleaning up of contaminated soil, sediment and water, it has not been commercialized and used extensively on a large scale. The present chapter discusses the strategies and applicability of mycoremediation mechanisms for heavy metal resistance/tolerance in plants.

Assessment of Anticancer Properties of Betelvine

Betelvine (Piper betle) leaves are known for its medicinal properties since 600 AD practiced in Ayurvedic system of medicine. It is a cash crop for many Southeast Asian countries and is, therefore, also known as “Green Gold.” Widely consumed as masticator, betelvine leaves are a rich source of phenolic compounds having antiproliferative, antimutagenic, antibacterial, and antioxidant properties. The Piper betel leaf (PBL) extract is used as an antiseptic in cuts and wounds, is used as a diuretic, helps in digestion, and treats boils, conjunctivitis, stomach problems, hysteria, itches, leucorrhea, and ringworm. Also, the PBL extract is used as adjunct in Ayurvedic medicines, and the essential oil obtained from the betelvine leaves has antimicrobial and antiprotozoal activities. The high amounts of phenolic compounds present in betelvine leaf extract are of antioxidant nature which plays a key role to serve several medicinal properties. Apart from these medicinal properties reported since Ayurvedic times, modern researches have proved them to bear anticancer properties too. The compounds that confer the anticancer activity to betelvine leaves include antioxidant compounds such as eugenol, hydroxychavicol, β-carotene, and ascorbic acid, all of which are known for scavenging free radicals, thereby preventing cellular damages. In the present chapter, we have discussed the advances in betelvine research in the field of cancer as a cancer suppressor, killing agent for cancer cells, as nutraceutical and other medicinal properties helpful in cancer therapy.

Reduced cell wall degradation plays a role in cow dung-mediated management of wilt complex disease of chickpea

Chickpea, a major pulse crop, is highly prone to a devastating wilt disease commonly caused by the complex interaction of soilborne fungal pathogens of the genus Fusarium, Rhizoctonia and Sclerotinia. These pathogens collectively cause both superficial and sunken lesions resulting in symptoms like wilting and yellowing causing plant losses at seedling stage and become a major limiting factor for its growth and yield. Earlier studies demonstrated the role of composted mixture in protection against soilborne pathogens. However, there is paucity of substantial evidence for the mechanism of protection. The present study predicts the probable mechanism of cow dung-mediated reduction of wilt in Cicer arietinum. Cow dung-coated seeds sown in presence of mixture of fungi (FCD) could reduce the activities of cell wall-degrading enzymes produced by plant roots in response to pathogens, which were otherwise higher in mixture of wilt complex fungi/pathogens (FUN) treatment. Reduction in transcript accumulation of related genes followed by histological studies showed intercellular fungal colonization in FUN treatment, whereas it was undetected in FCD. Results indicate that cow dung treatment of chickpea seeds reduces activities of the cell wall-degrading enzymes in a transcriptionally regulated manner, which in turn function as biocontrol measure for disease.