Browsing by Author "James F. White"

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Bacterial endophytes from rice cut grass (Leersia oryzoides L.) increase growth, promote root gravitropic response, stimulate root hair formation, and protect rice seedlings from disease
(Springer International Publishing, 2018) Satish K. Verma; Kathryn Kingsley; Marshall Bergen; Camille English; Matthew Elmore; Ravindra N. Kharwar; James F. White
Background and Aims: Leersia oryzoides, a wild relative of rice (Oryza sativa), may carry potential seed-borne bacterial endophytes which could be used to enhance growth of rice. We hypothesized that seed-associated bacteria from L. oryzoides would be compatible with rice and promote seedling growth, development, and survival. Methods: We isolated bacteria from seed of L. oryzoides and checked compatibility with rice as well as Bermuda grass seeds for seedling growth promotion. Internal colonisation of bacteria into root cells was observed by ROS staining and microscopic observation. Growth promoting bacteria were evaluated for IAA production, phosphate solubilization and antifungal activities. Results: Overall, ten bacteria were found to be growth promoting in rice seedlings with effects including restoration of root gravitropic response, increased root and shoot growth, and stimulation of root hair formation. All bacteria were identified by 16S rDNA sequencing. Six bacteria were found to become intracellular in root parenchyma and root hairs in rice and in Bermuda grass seedlings. Six bacteria were able to produce IAA in LB broth with highest (47.06 ± 1.99 μg ml−1) by LTE3 (Pantoea hericii). Nine isolates solubilized phosphate and inhibited at least one soil borne fungal pathogen. Conclusions: Seed bacteria of L. oryzoides are compatible with rice. Many of these bacteria become intracellular, induce root gravitropic response, increase root and shoot growth, and stimulate root hair formation in both rice and Bermuda grass seedlings. Presence of bacteria protects seedlings from soil pathogens during seedling establishment. This research suggests that bioprospecting microbes on near relatives of rice and other crop plants may be a viable strategy to obtain microbes to improve cultivation of crops. © 2017, Springer International Publishing AG.
Biocontrol Potential of Microbial Consortia: Approaches in Food Security and Disease Management
(Springer International Publishing, 2022) Hariom Verma; Chandra Kant; Sandeep Kumar Singh; James F. White; Ajay Kumar; Samir Droby
In the current scenario of climate change, the uncertainty of environmental factors and adverse impacts of chemical pesticides on the texture and productivity of soil along with increasing health concerns to humans appear as a global challenge in the management of agricultural yield to meet the food demand of burgeoning global populations. However, microbial consortia applied as either plant or soil inoculants have largely been used in the last few decades for the enhancement of agricultural productivity, improvement of nutrient status in the soil, improvement of fruit quality, and as biocontrol agents to control the growth of devastating phytopathogens during harvest or postharvest storage. The functional aspects of microbial consortia have been shown effective in broader ways as compared to individual cultures. Moreover, the efficiency of microbial consortia is higher due to the presence of several strains where each strain performs specific functions and shows better performance in functional behaviours in order to withstand environmental fluctuations. In this chapter, we have tried to compile the latest aspects and advancements in the development and application of microbial consortia for effective phytopathogen control so that the goals of food security could be achieved. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022.
Effect of bacterial endophyte on expression of defense genes in Indian popcorn against Fusarium moniliforme
(Springer Netherlands, 2015) Surendra K. Gond; Marshall S. Bergen; Mónica S. Torres; James F. White; Ravindra N. Kharwar
An endophytic Bacillus amyloliquefaciens subsp. subtilis was isolated from surface sterilized seedlings of tropical corn. To evaluate the hypothesis that this endophyte is defensive in nature and determine the mechanisms of host defense we examined the effects of the endophyte on pathogens and host disease resistance genes. The bacterial endophyte showed antifungal activity against fungal pathogens Fusarium moniliforme, Colletotrichum gloeosporioides and Aspergillus flavus. Plant protection activity was also observed in Indian popcorn seedlings inoculated with the endophyte against F. moniliforme. Gene expression analysis was conducted and demonstrated that up-regulation of several defense genes in corn was greater after 48 hours of pathogen challenge than 24 hours. Plant defense pathways triggered by the endophytic bacterium appeared to be SA (salicylic acid) independent. The abundance of the zm Jasmonic acid-induced gene expression was greater in pathogen challenged plants pre-treated with the endophytic bacterium than in the plants challenged only with pathogen. Pre-treatment with the endophytic bacterium resulted in a more intense induction of maize pathogenesis related protein genes PR-1 and PR-10 during interaction with F. moniliforme compared to plants that were treated only with the fungal pathogen. © 2015, Springer Science+Business Media Dordrecht.
Endophytic Burkholderia: Multifunctional roles in plant growth promotion and stress tolerance
(Elsevier GmbH, 2022) Gaurav Pal; Samiksha Saxena; Kanchan Kumar; Anand Verma; Pramod K. Sahu; Ashutosh Pandey; James F. White; Satish K. Verma
The genus Burkholderia has proven potential in improving plant performance. In recent decades, a huge diversity of Burkholderia spp. have been reported with diverse capabilities of plant symbiosis which could be harnessed to enhance plant growth and development. Colonization of endophytic Burkholderia spp. have been extensively studied through techniques like advanced microscopy, fluorescent labelling, PCR based assays, etc., and found to be systemically distributed in plants. Thus, use of these biostimulant microbes holds the promise of improving quality and quantity of crops. The endophytic Burkholderia spp. have been found to support plant functions along with boosting nutrient availability, especially under stress. Endophytic Burkholderia spp. improve plant survival against deadly pathogens via mechanisms like competition, induced systemic resistance, and antibiosis. At the same time, they are reported to extend plant tolerance towards multiple abiotic stresses especially drought, salinity, and cold. Several attempts have been made to decipher the potential of Burkholderia spp. by genome mining, and these bacteria have been found to harbour genes for plant symbiosis and for providing multiple benefits to host plants. Characteristics specific for host recognition and nutrient acquisition were confirmed in endophytic Burkholderia by genomics and proteomics-based studies. This could pave the way for harnessing Burkholderia spp. for biotechnological applications like biotransformation, phytoremediation, insecticidal activity, antimicrobials, etc. All these make Burkholderia spp. a promising microbial agent in improving plant performance under multiple adversities. Thus, the present review highlights critical roles of endophytic Burkholderia spp., their colonization, alleviation of biotic and abiotic stresses, biotechnological applications and genomic insights. © 2022 Elsevier GmbH
From ‘nitrosome’ to ‘nitroplast’: stages in the evolution of nitrogen-fixing organelles from free-living diazotrophs
(Springer Science and Business Media B.V., 2025) Satish K. Verma; James F. White
Microbial symbiosis has played an important role in evolution of life on Earth. Lynn Margulis proposed that eukaryotic cells have evolved through a series of intracellular interactions among prokaryotes in the very early stages of life on Earth. There are many current microbial interactions that suggest that complexity in organisms is being driven by symbiosis. For example, plants may establish an endosymbiosis with free-living soil microbes (e.g., Gluconacetobacter diazotrophicus or Burkholderia vietnamiensis) and sequester them in to cellular vesicles termed ‘nitrosomes’ where plants extract nitrogen from the endosymbionts. Similarly, a vesicular ‘symbiosome’ develops in root nodules of many legume family plants. Recently, scientists have discovered a new permanent nitrogen-fixing cell organelle, termed ‘nitroplast’, in the marine alga Braarudosphaera bigelowii. In this mini review we discuss nitrogen-fixing symbioses, and suggest that the ‘nitroplast’ may have been derived from ‘nitrosomes’. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.
Fungal disease prevention in seedlings of rice (Oryza sativa) and other grasses by growth-promoting seed-associated endophytic bacteria from invasive phragmites australis
(MDPI AG, 2018) Satish K. Verma; Kathryn L. Kingsley; Marshall S. Bergen; Kurt P. Kowalski; James F. White
Non-cultivated plants carry microbial endophytes that may be used to enhance development and disease resistance of crop species where growth-promoting and protective microbes may have been lost. During seedling establishment, seedlings may be infected by several fungal pathogens that are seed or soil borne. Several species of Fusarium, Pythium and other water moulds cause seed rots during germination. Fusarium blights of seedlings are also very common and significantly affect seedling development. In the present study we screened nine endophytic bacteria isolated from the seeds of invasive Phragmites australis by inoculating onto rice, Bermuda grass (Cynodon dactylon), or annual bluegrass (Poa annua) seeds to evaluate plant growth promotion and protection from disease caused by Fusarium oxysporum. We found that three bacteria belonging to genus Pseudomonas spp. (SLB4-P. fluorescens, SLB6-Pseudomonas sp. and SY1-Pseudomonas sp.) promoted seedling development, including enhancement of root and shoot growth, and stimulation of root hair formation. These bacteria were also found to increase phosphate solubilization in in vitro experiments. Pseudomonas sp. (SY1) significantly protected grass seedlings from Fusarium infection. In co-culture experiments, strain SY1 strongly inhibited fungal pathogens with 85.71% growth inhibition of F. oxysporum, 86.33% growth inhibition of Curvularia sp. and 82.14% growth inhibition of Alternaria sp. Seedlings previously treated with bacteria were found much less infected by F. oxysporum in comparison to non-treated controls. On microscopic observation we found that bacteria appeared to degrade fungal mycelia actively. Metabolite products of strain SY1 in agar were also found to inhibit fungal growth on nutrient media. Pseudomonas sp. (SY1) was found to produce antifungal volatiles. Polymerase chain reaction (PCR) amplification using specific primers for pyrrolnitirin synthesis and HCN (hydrogen cyanide) production suggested presence of genes for both compounds in the genome of SY1. HCN was detected in cultures of SY1. We conclude that microbes from non-cultivated plants may provide disease protection and promote growth of crop plants. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
Fungal endophytes as efficient sources of plant-derived bioactive compounds and their prospective applications in natural product drug discovery: Insights, avenues, and challenges
(MDPI AG, 2021) Archana Singh; Dheeraj K. Singh; Ravindra N. Kharwar; James F. White; Surendra K. Gond
Fungal endophytes are well-established sources of biologically active natural compounds with many producing pharmacologically valuable specific plant-derived products. This review details typical plant-derived medicinal compounds of several classes, including alkaloids, couma-rins, flavonoids, glycosides, lignans, phenylpropanoids, quinones, saponins, terpenoids, and xan-thones that are produced by endophytic fungi. This review covers the studies carried out since the first report of taxol biosynthesis by endophytic Taxomyces andreanae in 1993 up to mid-2020. The article also highlights the prospects of endophyte-dependent biosynthesis of such plant-derived pharmacologically active compounds and the bottlenecks in the commercialization of this novel approach in the area of drug discovery. After recent updates in the field of ‘omics’ and ‘one strain many compounds’ (OSMAC) approach, fungal endophytes have emerged as strong unconven-tional source of such prized products. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Pantoea spp. Associated with smooth crabgrass (Digitaria ischaemum) seed inhibit competitor plant species
(MDPI AG, 2019) Matthew T. Elmore; James F. White; Kathryn L. Kingsley; Katherine H. Diehl; Satish K. Verma
Digitaria ischaemum (Schreb.) Schreb. ex Muhl. and Poa annua L. are competitive, early successional species which are usually considered weeds in agricultural and turfgrass systems. Bacteria and fungi associated with D. ischaemum and P. annua seed may contribute to their competitiveness by antagonizing competitor forbs, and were studied in axenic culture. Pantoea spp. were the most common bacterial isolate of D. ischaemum seed, while Epicoccum and Curvularia spp. were common fungal isolates. A variety of species were collected from non-surface sterilized P. annua. Certain Pantoea spp. isolates were antagonistic to competitor forbs Taraxacum officinale, Trifolium repens. All bacterial isolates that affected T. officinale mortality were isolated from D. ischaemum seed while none of the P. annua isolates affected mortality. Two selected bacterial isolates identified as Pantoea ananatis were evaluated further on D. ischaemum, T. repens (a competitor forb) and P. annua (a competitor grass) alone and in combination with a Curvularia sp. fungus. These bacteria alone caused >65% T. repens seedling mortality but did not affect P. annua seedling mortality. These experiments demonstrate that Pantoea ananatis associated with D. ischaemum seeds is antagonistic to competitor forbs in axenic culture. The weedy character of D. ischaemum could at least in part stem from the possession of bacteria that are antagonistic to competitor species. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
Potential application of endophytic bacteria for induction of abiotic stress tolerance in plants
(Springer Science and Business Media B.V., 2025) Hemant Kumar; Rusi Lata; Uzma Khan; James F. White; Surendra Kumar Gond
Abiotic stress is one of the main problems in agriculture worldwide. Plants under abiotic stress suffer from a variety of morpho-anatomical, physiological, and biochemical changes that impact plant growth and development and have the possibility of significantly reducing the economic yield. Researchers have better-understood plant-microbe interactions under biotic and abiotic stress in the last several years. Endophytes are microorganisms that establish a symbiotic relationship with the host plant, exerting their presence without inducing any detrimental effects. Endophytic bacteria (EB) can regulate plant tolerance through different mechanisms, such as nutrient uptake, antioxidant enzyme activity, induction of plant development through phytohormones, and the synthesis of stress-responsive substances. Recent studies demonstrated that EB possesses the ability to elicit abiotic stress responses. EB has become a viable approach to augmenting agricultural yield and safeguarding plants against abiotic stresses. The present study provides an in-depth analysis of the significant EB contribution in facilitating plant growth and enhancing plant tolerance to abiotic stress such as drought, salinity, temperature fluctuations, heavy metal exposure, and nutrient-deficient conditions. This review addresses the role of EB in minimizing abiotic stress in plants. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.
Reactive Oxygen Defense Against Cellular Endoparasites and the Origin of Eukaryotes
(Elsevier, 2018) James F. White; Kathryn Kingsley; Carla J. Harper; Satish K. Verma; Lara Brindisi; Qiang Chen; Xiaoqian Chang; April Micci; Marshall Bergen
In this chapter, we propose a model for the early evolution of eukaryotic cells under pressure of intense endoparasitism. We define features of eukaryotes developed to defend against endoparasites (primarily bacteria), including a defensive system composed of an antioxidant sterol-enriched internal and external membrane system that could be used to entrap endoparasites and degrade them with superoxide produced on the membranes, cytoskeleton scaffolding for the membrane system, and a nuclear envelope to exclude endoparasites from reaching the genome. Mitochondria and chloroplasts evolved from the prokaryotes that developed ways to neutralize the reactive oxygen defense of the host. For mitochondria, hydrogen pumping to the exterior of the endoparasite enabled them to reduce superoxide to water, effectively defeating the host defense. Other features of eukaryotes that may have evolved from defense from endoparasitism include: autophagy, cell walls in fungi and plants, acquired immunity in animals, multicellularity, and apoptosis. We evaluate fossil data, where available, to provide additional information regarding the early evolution of eukaryotes and the prevalence of endoparasitic microbes. © 2018 Elsevier Inc. All rights reserved.
Rhizophagy cycle: An oxidative process in plants for nutrient extraction from symbiotic microbes
(MDPI AG, 2018) James F. White; Kathryn L. Kingsley; Satish K. Verma; Kurt P. Kowalski
In this paper, we describe a mechanism for the transfer of nutrients from symbiotic microbes (bacteria and fungi) to host plant roots that we term the ‘rhizophagy cycle.’ In the rhizophagy cycle, microbes alternate between a root intracellular endophytic phase and a free-living soil phase. Microbes acquire soil nutrients in the free-living soil phase; nutrients are extracted through exposure to host-produced reactive oxygen in the intracellular endophytic phase. We conducted experiments on several seed-vectored microbes in several host species. We found that initially the symbiotic microbes grow on the rhizoplane in the exudate zone adjacent the root meristem. Microbes enter root tip meristem cells—locating within the periplasmic spaces between cell wall and plasma membrane. In the periplasmic spaces of root cells, microbes convert to wall-less protoplast forms. As root cells mature, microbes continue to be subjected to reactive oxygen (superoxide) produced by NADPH oxidases (NOX) on the root cell plasma membranes. Reactive oxygen degrades some of the intracellular microbes, also likely inducing electrolyte leakage from microbes—effectively extracting nutrients from microbes. Surviving bacteria in root epidermal cells trigger root hair elongation and as hairs elongate bacteria exit at the hair tips, reforming cell walls and cell shapes as microbes emerge into the rhizosphere where they may obtain additional nutrients. Precisely what nutrients are transferred through rhizophagy or how important this process is for nutrient acquisition is still unknown. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
Seed Endophytic Bacteria of Pearl Millet (Pennisetum glaucum L.) Promote Seedling Development and Defend Against a Fungal Phytopathogen
(Frontiers Media S.A., 2021) Kanchan Kumar; Anand Verma; Gaurav Pal; Anubha; James F. White; Satish K. Verma
Seed endophytic bacteria (SEB) are primary symbionts that play crucial roles in plant growth and development. The present study reports the isolation of seven culturable SEB including Kosakonia cowanii (KAS1), Bacillus subtilis (KAS2), Bacillus tequilensis (KAS3), Pantoea stewartii (KAS4), Paenibacillus dendritiformis (KAS5), Pseudomonas aeruginosa (KAS6), and Bacillus velezensis (KAS7) in pearl millet seeds. All the isolates were characterized for their plant growth promoting activities. Most of the SEB also inhibited the growth of tested fungal phytopathogens in dual plate culture. Removal of these SEB from seeds compromised the growth and development of seedlings, however, re-inoculation with the SEB (Kosakonia cowanii, Pantoea stewartii, and Pseudomonas aeruginosa) restored the growth and development of seedlings significantly. Fluorescence microscopy showed inter and intracellular colonization of SEB in root parenchyma and root hair cells. Lipopeptides were extracted from all three Bacillus spp. which showed strong antifungal activity against tested fungal pathogens. Antifungal lipopeptide genes were also screened in Bacillus spp. After lipopeptide treatment, live-dead staining with fluorescence microscopy along with bright-field and scanning electron microscopy (SEM) revealed structural deformation and cell death in Fusarium mycelia and spores. Furthermore, the development of pores in the membrane and leakages of protoplasmic substances from cells and ultimately death of hyphae and spores were also confirmed. In microcosm assays, treatment of seeds with Bacillus subtilis or application of its lipopeptide alone significantly protected seedlings from Fusarium sp. infection. Copyright © 2021 Kumar, Verma, Pal, Anubha, White and Verma.
Special Issue “Microbial Endophytes: Functional Biology and Applications”: Editorial
(MDPI, 2023) Ajay Kumar; Gustavo Santoyo; James F. White; Virendra Kumar Mishra
[No abstract available]
The potential application of endophytes in management of stress from drought and salinity in crop plants
(MDPI AG, 2021) Hariom Verma; Dharmendra Kumar; Vinod Kumar; Madhuree Kumari; Sandeep Kumar Singh; Vijay Kumar Sharma; Samir Droby; Gustavo Santoyo; James F. White; Ajay Kumar
Endophytic microorganisms present inside the host plant play an essential role in host fitness, nutrient supply and stress tolerance. Endophytes are often used in sustainable agriculture as biofertilizers, biopesticides and as inoculants to mitigate abiotic stresses including salinity, drought, cold and pH variation in the soil. In changing climatic conditions, abiotic stresses create global challenges to achieve optimum crop yields in agricultural production. Plants experience stress conditions that involve endogenous boosting of their immune system or the overexpression of their defensive redox regulatory systems with increased reactive oxygen species (ROS). However, rising stress factors overwhelm the natural redox protection systems of plants, which leads to massive internal oxidative damage and death. Endophytes are an integral internal partner of hosts and have been shown to mitigate abiotic stresses via modulating local or systemic mechanisms and producing antioxidants to counteract ROS in plants. Advancements in omics and other technologies have been made, but potential application of endophytes remains largely unrealized. In this review article, we will discuss the diversity, population and interaction of endophytes with crop plants as well as potential applications in abiotic stress management. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
The role of seed-vectored endophytes in seedling development and establishment
(Springer Netherlands, 2019) Satish K. Verma; Ravindra N. Kharwar; James F. White
Seed-vectored endophytes internally colonize plant seeds and remain without eliciting disease symptoms. Microbes are carried by seeds generation after generation to benefit the host during and following seed germination. Seed-vectored endophytes have been poorly investigated and research targeted at understanding their biology will have immense applications in agriculture and horticulture. Some reports are available on the roles of seed endophytes in plant growth promotion via nutrient acquisition and biocontrol of soil borne diseases, but mechanisms of interaction at the endophyte-host interface, especially during seed germination and seedling establishment, have not been explored adequately. The present paper is intended to review the role of seed vectored endophytes in seed germination, seedlings development and in developing the rhizosphere community. The mechanisms of interaction and movement of seed inhabiting endophytic bacteria are explained with the help of pictorial models. © 2019, Springer Nature B.V.