Characterization of a cold-tolerant plant growth-promoting bacterium Pantoea dispersa 1A isolated from a sub-alpine soil in the North Western Indian Himalayas

Biodiversity in mountain soils above the treeline

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

Disruption and recovery of outdoor bioaerosols before, during, and after the COVID-19 outbreak at a campus in Central China: pathogen composition, particle size distribution, influencing factors, and exposure risk

Before (2019), during (2020), and after (2021) the COVID-19 outbreak, different response methods and measures were taken on campuses to control the spread of COVID-19 within schools. These response methods may have changed the outdoor bioaerosol characteristics, which may affect staff and student health. Therefore, we analyzed the bacterial concentrations, particle size distribution, microbial populations, exposure risks, and environmental influences of bioaerosols at a campus before, during, and after the COVID-19 outbreak. This study used eight-stage Andersen samplers to collect and analyze culturable bacteria in bioaerosols from various locations, high-throughput sequencing to analyze microbial species, principal component analysis to compare differences in samples, RDA to investigate the effects of environmental factors on bioaerosols, and hazard quotient (HQ) and BugBase to evaluate human health risks. The study findings revealed that average bacterial concentrations before, during, and after COVID-19 were 75 CFU m-3, 136 CFU m-3, and 78 CFU m-3, respectively. Moreover, the average percentage of bacteria attached to PM2.5 was 49.2%, 42.7%, and 29.9%, respectively. High-throughput sequencing revealed that species composition changed significantly during the three years of COVID-19. The proportion of Pantoea and Bacillus increased with the development of COVID-19 and these became the dominant strains after COVID-19, whereas Pseudomonas had the maximum proportion during COVID-19. Both risk assessment and BugBase phenotype prediction results indicated that the potential pathogenic risk was the highest in the outdoor environment of the campus during COVID-19 and that bioaerosol contamination was the most severe compared to the outdoor bioaerosol characteristics of the campus recovered after COVID-19.

Plant-Disease-Suppressive and Growth-Promoting Activities of Endophytic and Rhizobacterial Isolates Associated with Citrullus colocynthis

This study was conducted to investigate the antagonistic potential of endophytic and rhizospheric bacterial isolates obtained from Citrullus colocynthis in suppressing Fusarium solani and Pythium aphanidermatum and promoting the growth of cucumber. Molecular identification of bacterial strains associated with C. colocynthis confirmed that these strains belong to the Achromobacter, Pantoea, Pseudomonas, Rhizobium, Sphingobacterium, Bacillus, Sinorhizobium, Staphylococcus, Cupriavidus, and Exiguobacterium genera. A dual culture assay showed that nine of the bacterial strains exhibited antifungal activity, four of which were effective against both pathogens. Strains B27 (Pantoea dispersa) and B28 (Exiguobacterium indicum) caused the highest percentage of inhibition towards F. solani (48.5% and 48.1%, respectively). P. aphanidermatum growth was impeded by the B21 (Bacillus cereus, 44.7%) and B28 (Exiguobacterium indicum, 51.1%) strains. Scanning electron microscopy showed that the strains caused abnormality in phytopathogens' mycelia. All of the selected bacterial strains showed good IAA production (>500 ppm). A paper towel experiment demonstrated that these strains improved the seed germination, root/shoot growth, and vigor index of cucumber seedlings. Our findings suggest that the bacterial strains from C. colocynthis are suppressive to F. solani and P. aphanidermatum and can promote cucumber growth. This appears to be the first study to report the efficacy of these bacterial strains from C. colocynthis against F. solani and P. aphanidermatum.

Isolation and Identification of a Phosphate-Solubilizing Pantoea dispersa with a Saline-Alkali Tolerance and Analysis of Its Growth-Promoting Effects on Silage Maize Under Saline-Alkali Field Conditions

Phosphate-solubilizing bacteria (PSB) are microorganisms that can dissolve insoluble phosphorus (P) to accessible forms. This study aimed to screen saline-alkali-tolerant PSB and analyze its growth promoting properties, and evaluate its effects on the growth, quality, soil nutrient balance, and enzyme activities of silage maize in the field. We isolated six phosphate-solubilizing strains from rhizosphere soil of silage maize planted in saline-alkali land, and FC-1 with the best P-solubilizing effect was used for further study. The morphological, physiological and biochemical analysis, and 16S rDNA and housekeeping gene atpD sequencing were performed for identification. FC-1 was identified as Pantoea dispersa and had high P solubility. The phosphate solubility of FC-1 using four P sources ranged from 160.79 to 270.22 mg l-1. FC-1 produced indole-3-acetic acid (IAA) and decreased the pH of the growth media by secreting organic acids, including citric acid, malic acid, succinic acid, and acetic acid. The results of a field experiment indicated that FC-1 treatment increased the height, stem diameter, fresh weight, dry weight, starch content, crude protein content, and total P content of silage maize by 9.8, 9.2, 12.6, 11.7, 12.6, 18.3, and 17.4%, respectively. The nitrogen, potassium, phosphorus, and organic matter contents in the rhizosphere soil of silage maize increased by 29.8, 17.1, 17.9, and 25.3%, respectively; urease, catalase, sucrase, and alkaline phosphatase levels also increased by 24.7, 26.7, 24.0, and 19.5%, respectively. FC-1 promoted the growth of silage maize by improving nutrient metabolism and enzyme activities in saline-alkali soil and may be an effective alternative to fertilizers.

Unveiling the duality of Pantoea dispersa: A mini review

Pantoea dispersa is a Gram-negative bacterium that exists in a variety of environments and has potential in many commercial and agricultural applications, such as biotechnology, environmental protection, soil bioremediation, and plant growth stimulation. However, P. dispersa is also a harmful pathogen to both humans and plants. This "double-edged sword" phenomenon is not uncommon in nature. To ensure survival, microorganisms respond to both environmental and biological stimuli, which could be beneficial or detrimental to other species. Therefore, to harness the full potential of P. dispersa, while minimizing potential harm, it is imperative to unravel its genetic makeup, understand its ecological interactions and underlying mechanisms. This review aims to provide a comprehensive and up-to-date overview of the genetic and biological characteristics of P. dispersa, in addition to potential impacts on plants and humans, as well as to provide insights into potential applications.

Within-host adaptation alters priority effects within the tomato phyllosphere microbiome

To predict the composition and function of ecological communities over time, it is essential to understand how in situ evolution alters priority effects between resident and invading species. Phyllosphere microbial communities are a useful model system to explore priority effects because the system is clearly spatially delineated and can be manipulated experimentally. We conducted an experimental evolution study with tomato plants and the early-colonizing bacterium species Pantoea dispersa, exploring priority effects when P. dispersa was introduced before, simultaneously with or after competitor species. P. dispersa rapidly evolved to invade a new niche within the plant tissue and altered its ecological interactions with other members of the plant microbiome and its effect on the host. Prevailing models have assumed that adaptation primarily improves the efficiency of resident species within their existing niches, yet in our study system, the resident species expanded its niche instead. This finding suggests potential limitations to the application of existing ecological theory to microbial communities.

Reconnoitering the capabilities of nodule endophytic Pantoea dispersa for improved nodulation and grain yield of chickpea (Cicer arietinum L.)

Microorganisms belonging to root and soil provide a wide range of services and benefits to the plant by promoting plant growth and controlling phytopathogens. This study aimed to isolate endophytic bacteria from the root nodules of chickpea (Cicer arietinum L.) and determine their potential in improving plant growth. A total of nineteen different bacterial morphotypes were isolated from root nodules of chickpea and characterized in vitro for plant growth promotion abilities. All bacterial isolates were able to produce indole acetic acid at varying levels, out of which MCA19 was screened as the most efficient indole acetic acid producer (10.25 µg mL^-1). MCA8, MCA9, MCA10, MCA11, MCA16, MCA17 and MCA19 were positive for phosphate solubilization, out of which MCA9 was best phosphate solubilizer (18.8 µg mL^-1). All bacterial strains showed varying ability to grow on nitrogen-free media. Hydrogen cyanide, pectinase, and cellulase production ability were also observed in isolates, in which MCA9, MCA12, MCA17 and MCA19 were found best. Based on in vitro testing, five isolates MCA2, MCA9, MCA11, MCA17 and MCA19 were selected for further studies. Bacterial isolates MCA9, MCA11, MCA17 and MCA19 were identified by 16S rRNA gene sequence analysis as Pantoea dispersa while MCA2 as Rhizobium pusense. This is the first report on the existence of Pantoea dispersa in the root nodules of chickpea. In pot experiment, a maximum increase of 30% was recorded in plant dry weight upon the application of MCA19. Under field conditions, bacterial isolates, MCA2, MCA11 and MCA19 significantly enhanced nodulation and yield parameters of chickpea, compared to control. Pantoea dispersa MCA19 displayed the highest plant growth-promoting potential by increasing 38% grain yield. Our results indicate that Pantoea dispersa MCA19 is a promising biofertilizer for future applications.

Relieving your stress: PGPB associated with Andean xerophytic plants are most abundant and active on the most extreme slopes

Introduction

Plants interact with plant growth-promoting bacteria (PGPB), especially under stress condition in natural and agricultural systems. Although a potentially beneficial microbiome has been found associated to plants from alpine systems, this plant- PGPB interaction has been scarcely studied. Nevados de Chillán Complex hold one of the southernmost xerophytic formations in Chile. Plant species living there have to cope with drought and extreme temperatures during the growing season period, microclimatic conditions that become harsher on equatorial than polar slopes, and where the interaction with PGPB could be key for plant survival. Our goal was to study the abundance and activity of different PGPB associated to two abundant plant species of Andean xerophytic formations on contrasting slopes.

Methods

Twenty individuals of Berberis empetrifolia and Azorella prolifera shrubs were selected growing on a north and south slope nearby Las Fumarolas, at 2,050 m elevation. On each slope, microclimate based on temperature and moisture conditions were monitored throughout the growing period (oct. - apr.). Chemical properties of the soil under plant species canopies were also characterized. Bacterial abundance was measured as Log CFU g^-1 from soil samples collected from each individual and slope. Then, the most abundant bacterial colonies were selected, and different hormonal (indoleacetic acid) and enzymatic (nitrogenase, phosphatase, ACC-deaminase) mechanisms that promote plant growth were assessed and measured.

Results and Discussion

Extreme temperatures were observed in the north facing slope, recording the hottest days (41 vs. 36°C) and coldest nights (-9.9 vs. 6.6°C). Moreover, air and soil moisture were lower on north than on south slope, especially late in the growing season. We found that bacterial abundance was higher in soils on north than on south slope but only under B. empetrifolia canopy. Moreover, the activity of plant growth-promoting mechanisms varied between slopes, being on average higher on north than on south slope, but with plant species-dependent trends. Our work showed how the environmental heterogeneity at microscale in alpine systems (slope and plant species identity) underlies variations in the abundance and plant growth promoting activity of the microorganisms present under the plant canopy of the Andean xerophytic formations and highlight the importance of PGPB from harsh systems as biotechnological tools for restoration.

Silicon and soil microorganisms improve rhizospheric soil health with bacterial community, plant growth, performance and yield

The interaction of silicon and soil microorganisms stimulates crop enhancement to ensure sustainable agriculture. Silicon may potentially increase nutrient availability in rhizosphere with improved plants' growth, development as it does not produce phytotoxicity. The rhizospheric microbiome accommodates a variety of microbial species that live in a small area of soil directly associated with the hidden half plants' system. Plant growth-promoting rhizobacteria (PGPR) play a major role in plant development in response to adverse climatic conditions. PGPRs may enhance the growth, quality, productivity in variety of crops, and mitigate abiotic stresses by reprogramming stress-induced physiological variations in plants via different mechanisms, such as synthesis of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, exopolysaccharides, volatile organic compounds, atmospheric nitrogen fixation, and phosphate solubilization. Our article eye upon interactions of silicon and plant microbes which seems to be an opportunity for sustainable agriculture for series of crops and cropping systems in years to come, essential to safeguard the food security for masses.

Validation of Species-Specific PCR Assays for the Detection of Pantoea ananatis, P. agglomerans, P. allii, and P. stewartii

Species of Pantoea represent a group of plant pathogenic bacteria that infect a variety of agro-economically important plant species. Among these, a complex of P. ananatis, P. allii, P. agglomerans, and P. stewartii subsp. indologenes cause center rot in onion, resulting in significant economic losses. As species of Pantoea are phenotypically closely related, identification of Pantoea species relies on the sequencing and phylogenetic analysis of housekeeping genes. To aid in rapid identification of Pantoea species, efforts have been made in developing species-specific primers to be used in PCR assays. In the current study, two P. ananatis, one P. allii, one P. agglomerans, and three P. stewartii published primers as well as newly developed P. agglomerans PagR primers were evaluated for their specificity against 79 Pantoea strains, belonging to 15 different species. To ensure that selected primers were evaluated against accurately identified species, sequencing and phylogenetic analysis of housekeeping gene infB were conducted. Thereafter, PCR assays using selected species-specific primers were performed. The results showed that previously described P. ananatis-specific PANA_1008; P. allii-specific allii-leuS; P. stewartii-specific PANST_rpoB, 3614galE, and DC283galE primers; and one newly designed P. agglomerans-specific PagR primer pair were highly specific for their target Pantoea species. They accurately identified these strains into their species and, in some cases, their subspecies level. The findings of the current study will facilitate rapid and reliable identification of P. ananatis, P. agglomerans, P. allii, and P. stewartii.

Mitigating abiotic stress: microbiome engineering for improving agricultural production and environmental sustainability

The responses of plants to different abiotic stresses and mechanisms involved in their mitigation are discussed. Production of osmoprotectants, antioxidants, enzymes and other metabolites by beneficial microorganisms and their bioengineering ameliorates environmental stresses to improve food production. Progressive intensification of global agriculture, injudicious use of agrochemicals and change in climate conditions have deteriorated soil health, diminished the microbial biodiversity and resulted in environment pollution along with increase in biotic and abiotic stresses. Extreme weather conditions and erratic rains have further imposed additional stress for the growth and development of plants. Dominant abiotic stresses comprise drought, temperature, increased salinity, acidity, metal toxicity and nutrient starvation in soil, which severely limit crop production. For promoting sustainable crop production in environmentally challenging environments, use of beneficial microbes has emerged as a safer and sustainable means for mitigation of abiotic stresses resulting in improved crop productivity. These stress-tolerant microorganisms play an effective role against abiotic stresses by enhancing the antioxidant potential, improving nutrient acquisition, regulating the production of plant hormones, ACC deaminase, siderophore and exopolysaccharides and accumulating osmoprotectants and, thus, stimulating plant biomass and crop yield. In addition, bioengineering of beneficial microorganisms provides an innovative approach to enhance stress tolerance in plants. The use of genetically engineered stress-tolerant microbes as inoculants of crop plants may facilitate their use for enhanced nutrient cycling along with amelioration of abiotic stresses to improve food production for the ever-increasing population. In this chapter, an overview is provided about the current understanding of plant-bacterial interactions that help in alleviating abiotic stress in different crop systems in the face of climate change. This review largely focuses on the importance and need of sustainable and environmentally friendly approaches using beneficial microbes for ameliorating the environmental stresses in our agricultural systems.

A Global Network Meta-Analysis of the Promotion of Crop Growth, Yield, and Quality by Bioeffectors

Bioeffector (BE) application is emerging as a strategy for achieving sustainable agricultural practices worldwide. However, the effect of BE on crop growth and quality is still controversial and there is still no adequate impact assessment that determines factors on the efficiency of BE application. Therefore, we carried out a network metaanalysis on the effect of BEs using 1,791 global observations from 186 studies to summarize influencing factors and the impact of BEs on crop growth, quality, and nutrient contents. The results show that BEs did not only improve plant growth by around 25% and yield by 30%, but also enhanced crop quality, e.g., protein (55% increase) and soluble solids content (75% increase) as well as aboveground nitrogen (N) and phosphate (P) content by 28 and 40%, respectively. The comparisons among BE types demonstrated that especially non-microbial products, such as extracts and humic/amino acids, have the potential to increase biomass growth by 40-60% and aboveground P content by 54-110%. The soil pH strongly influenced the efficiency of the applied BE with the highest effects in acidic soils. Our results showed that BEs are most suitable for promoting the quality of legumes and increasing the yield of fruits, herbs, and legumes. We illustrate that it is crucial to optimize the application of BEs with respect to the right application time and technique (e.g., placement, foliar). Our results provide an important basis for future research on the mechanisms underlying crop improvement by the application of BEs and on the development of new BE products.

Application of Psychrotolerant Antarctic Bacteria and Their Metabolites as Efficient Plant Growth Promoting Agents

Iron is the fourth most abundant element on earth. However, its low bioavailability is a key plant-growth limiting factor. Bacteria play an important role in plant growth promotion since they produce specific secondary metabolites that may increase macro- and micronutrient accessibility in soil. Therefore, bacterial-derived iron chelators, as well as surface-active compounds, are recognised as essential to plant welfare. In this study, three cold-active Antarctic bacterial strains, i.e. Pseudomonas sp. ANT_H12B, Psychrobacter sp. ANT_H59 and Bacillus sp. ANT_WA51, were analysed. The physiological and genomic characterisation of these strains revealed their potential for plant growth promotion, reflected in the production of various biomolecules, including biosurfactants (that may lower the medium surface tension of even up to 53%) and siderophores (including ANT_H12B-produced mixed-type siderophore that demonstrated the highest production, reaching the concentration of up to 1.065 mM), increasing the availability of nutrients in the environment and neutralising fungal pathogens. Tested bacteria demonstrated an ability to promote the growth of a model plant, alfalfa, increasing shoots’ length and fresh biomass even up to 26 and 46% respectively; while their metabolites increased the bioavailability of iron in soil up to 40%. It was also revealed that the introduced strains did not disrupt physicochemical conditions and indigenous soil microbial composition, which suggests that they are promising amendments preserving the natural biodiversity of soil and increasing its fertility.

The Potential Role of Microbial Biostimulants in the Amelioration of Climate Change-Associated Abiotic Stresses on Crops

Crop plants are more often exposed to abiotic stresses in the current age of fast-evolving climate change. This includes exposure to extreme and unpredictable changes in climatic conditions, phytosanitary hazards, and cultivation conditions, which results in drastic losses in worldwide agricultural productions. Plants coexist with microbial symbionts, some of which play key roles in the ecosystem and plant processes. The application of microbial biostimulants, which take advantage of symbiotic relationships, is a long-term strategy for improving plant productivity and performance, even in the face of climate change-associated stresses. Beneficial filamentous fungi, yeasts, and bacteria are examples of microbial biostimulants, which can boost the growth, yield, nutrition and stress tolerance in plants. This paper highlights recent information about the role of microbial biostimulants and their potential application in mitigating the abiotic stresses occurring on crop plants due to climate change. A critical evaluation for their efficient use under diverse climatic conditions is also made. Currently, accessible products generally improve cultural conditions, but their action mechanisms are mostly unknown, and their benefits are frequently inconsistent. Thus, further studies that could lead to the more precisely targeted products are discussed.

R, Choudhary AK, Salam MD, Sahoo MR, Bhutia TL, Devi SH, Thounaojam AS, Behera C, M. N. H, Kumar A, Dasgupta M, Devi YP, Singh D, Bhagowati S, Devi CP, Singh HR, Khaba CI. Role of biostimulants in mitigating the effects of climate change on crop performance

Climate change is a critical yield-limiting factor that has threatened the entire global crop production system in the present scenario. The use of biostimulants in agriculture has shown tremendous potential in combating climate change-induced stresses such as drought, salinity, temperature stress, etc. Biostimulants are organic compounds, microbes, or amalgamation of both that could regulate plant growth behavior through molecular alteration and physiological, biochemical, and anatomical modulations. Their nature is diverse due to the varying composition of bioactive compounds, and they function through various modes of action. To generate a successful biostimulatory action on crops under different parameters, a multi-omics approach would be beneficial to identify or predict its outcome comprehensively. The 'omics' approach has greatly helped us to understand the mode of action of biostimulants on plants at cellular levels. Biostimulants acting as a messenger in signal transduction resembling phytohormones and other chemical compounds and their cross-talk in various abiotic stresses help us design future crop management under changing climate, thus, sustaining food security with finite natural resources. This review article elucidates the strategic potential and prospects of biostimulants in mitigating the adverse impacts of harsh environmental conditions on plants.

Harnessing Synergistic Biostimulatory Processes: A Plausible Approach for Enhanced Crop Growth and Resilience in Organic Farming

Simple Summary

Demand for organically grown crops has risen globally due to its healthier and safer food products. From a sustainability perspective, organic farming offers an eco-friendly cultivation system that minimizes agrochemicals and producing food with little or no environmental footprint. However, organic agriculture’s biggest drawback is the generally lower and variable yield in contrast to conventional farming. Compatible with organic farming, the selective use of biostimulants can close the apparent yield gap between organic and conventional cultivation systems. A biostimulant is defined as natural microorganisms (bacteria, fungi) or biologically active substances that are able to improve plant growth and yield through several processes. Biostimulants are derived from a range of natural resources including organic materials (composts, seaweeds), manures (earthworms, fish, insects) and extracts derived from microbes, plant, insect or animal origin. The current trend is indicative that a mixture of biostimulants is generally delivering better growth, yield and quality rather than applying biostimulant individually. When used correctly, biostimulants are known to help plants cope with stressful situations like drought, salinity, extreme temperatures and even certain diseases. More research is needed to understand the different biostimulants, key components, and also to adjust the formulations to improve their reliability in the field.

Abstract

Demand for organically grown food crops is rising substantially annually owing to their contributions to human health. However, organic farm production is still generally lower compared to conventional farming. Nutrient availability, content consistency, uptake, assimilation, and crop responses to various stresses were reported as critical yield-limiting factors in many organic farming systems. In recent years, plant biostimulants (BSs) have gained much interest from researchers and growers, and with the objective of integrating these products to enhance nutrient use efficiency (NUE), crop performance, and delivering better stress resilience in organic-related farming. This review gave an overview of direct and indirect mechanisms of microbial and non-microbial BSs in enhancing plant nutrient uptake, physiological status, productivity, resilience to various stressors, and soil-microbe-plant interactions. BSs offer a promising, innovative and sustainable strategy to supplement and replace agrochemicals in the near future. With greater mechanistic clarity, designing purposeful combinations of microbial and non-microbial BSs that would interact synergistically and deliver desired outcomes in terms of acceptable yield and high-quality products sustainably will be pivotal. Understanding these mechanisms will improve the next generation of novel and well-characterized BSs, combining microbial and non-microbial BSs strategically with specific desired synergistic bio-stimulatory action, to deliver enhanced plant growth, yield, quality, and resilience consistently in organic-related cultivation.

Implications of Seed Vault Storage Strategies for Conservation of Seed Bacterial Microbiomes

Global seed vaults are important, as they conserve plant genetic resources for future breeding to improve crop yield and quality and to overcome biotic and abiotic stresses. However, little is known about the impact of standard storage procedures, such as seed drying and cold storage on the seed bacterial community, and the ability to recover seed-associated bacteria after storage. In this study, soybean [Glycine max (L.) Merr.] seeds were analyzed to characterize changes in the bacterial community composition and culturability under varying storage conditions. The G. max bacterial microbiome was analyzed from undried seed, dried seed, and seed stored for 0, 3, 6, and 14months. Storage temperatures consisted of -20°C, 4°C, and room temperature (RT), with -20°C being commonly used in seed storage vaults globally. The seed microbiome of G. max was dominated by Gammaproteobacteria under all conditions. Undried seed was dominated by Pantoea (33.9%) and Pseudomonas (51.1%); however, following drying, the abundance of Pseudomonas declined significantly (0.9%), Pantoea increased significantly (73.6%), and four genera previously identified including Pajaroellobacter, Nesterenkonia, env.OPS_17, and Acidibacter were undetectable. Subsequent storage at RT, 4, or -20°C maintained high-abundance Genera at the majority of time points, although RT caused greater fluctuations in abundances. For many of the low-abundance Genera, storage at -20°C resulted in their gradual disappearance, whereas storage at 4°C or RT resulted in their more rapid disappearance. The changes in seed bacterial composition were reflected by cultured bacterial taxa obtained from the stored G. max seed. The main taxa were largely culturable and had similar relative abundance, while many, but not all, of the low-abundance taxa were also culturable. Overall, these results indicate that the initial seed drying affects the seed bacterial composition, suggesting that microbial isolation prior to seed drying is recommended to conserve these microbes. The standard seed storage condition of -20°C is most suitable for conservation of the bacterial seed microbiome, as this storage temperature slows down the loss of seed bacterial diversity over longer time periods, particularly low-abundance taxa.

Psychrophilic Bacterial Phosphate-Biofertilizers: A Novel Extremophile for Sustainable Crop Production under Cold Environment

Abiotic stresses, including low-temperature environments, adversely affect the structure, composition, and physiological activities of soil microbiomes. Also, low temperatures disturb physiological and metabolic processes, leading to major crop losses worldwide. Extreme cold temperature habitats are, however, an interesting source of psychrophilic and psychrotolerant phosphate solubilizing bacteria (PSB) that can ameliorate the low-temperature conditions while maintaining their physiological activities. The production of antifreeze proteins and expression of stress-induced genes at low temperatures favors the survival of such organisms during cold stress. The ability to facilitate plant growth by supplying a major plant nutrient, phosphorus, in P-deficient soil is one of the novel functional properties of cold-tolerant PSB. By contrast, plants growing under stress conditions require cold-tolerant rhizosphere bacteria to enhance their performance. To this end, the use of psychrophilic PSB formulations has been found effective in yield optimization under temperature-stressed conditions. Most of the research has been done on microbial P biofertilizers impacting plant growth under normal cultivation practices but little attention has been paid to the plant growth-promoting activities of cold-tolerant PSB on crops growing in low-temperature environments. This scientific gap formed the basis of the present manuscript and explains the rationale for the introduction of cold-tolerant PSB in competitive agronomic practices, including the mechanism of solubilization/mineralization, release of biosensor active biomolecules, molecular engineering of PSB for increasing both P solubilizing/mineralizing efficiency, and host range. The impact of extreme cold on the physiological activities of plants and how plants overcome such stresses is discussed briefly. It is time to enlarge the prospects of psychrophilic/psychrotolerant phosphate biofertilizers and take advantage of their precious, fundamental, and economical but enormous plant growth augmenting potential to ameliorate stress and facilitate crop production to satisfy the food demands of frighteningly growing human populations. The production and application of cold-tolerant P-biofertilizers will recuperate sustainable agriculture in cold adaptive agrosystems.

Utilization of Microbial Consortia as Biofertilizers and Biopesticides for the Production of Feasible Agricultural Product

Farmers are now facing a reduction in agricultural crop yield, due to the infertility of soils and poor farming. The application of chemical fertilizers distresses soil fertility and also human health. Inappropriate use of chemical fertilizer leads to the rapid decline in production levels in most parts of the world, and hence requires the necessary standards of good cultivation practice. Biofertilizers and biopesticides have been used in recent years by farmers worldwide to preserve natural soil conditions. Biofertilizer, a replacement for chemical fertilizer, is cost-effective and prevents environmental contamination to the atmosphere, and is a source of renewable energy. In contrast to chemical fertilizers, biofertilizers are cost-effective and a source of renewable energy that preserves long-term soil fertility. The use of biofertilizers is, therefore, inevitable to increase the earth's productivity. A low-input scheme is feasible to achieve farm sustainability through the use of biological and organic fertilizers. This study investigates the use of microbial inoculants as biofertilizers to increase crop production.

Plant Responses to Abiotic Stresses and Rhizobacterial Biostimulants: Metabolomics and Epigenetics Perspectives

In response to abiotic stresses, plants mount comprehensive stress-specific responses which mediate signal transduction cascades, transcription of relevant responsive genes and the accumulation of numerous different stress-specific transcripts and metabolites, as well as coordinated stress-specific biochemical and physiological readjustments. These natural mechanisms employed by plants are however not always sufficient to ensure plant survival under abiotic stress conditions. Biostimulants such as plant growth-promoting rhizobacteria (PGPR) formulation are emerging as novel strategies for improving crop quality, yield and resilience against adverse environmental conditions. However, to successfully formulate these microbial-based biostimulants and design efficient application programs, the understanding of molecular and physiological mechanisms that govern biostimulant-plant interactions is imperatively required. Systems biology approaches, such as metabolomics, can unravel insights on the complex network of plant-PGPR interactions allowing for the identification of molecular targets responsible for improved growth and crop quality. Thus, this review highlights the current models on plant defence responses to abiotic stresses, from perception to the activation of cellular and molecular events. It further highlights the current knowledge on the application of microbial biostimulants and the use of epigenetics and metabolomics approaches to elucidate mechanisms of action of microbial biostimulants.

Identification of Plant Growth Promoting Rhizobacteria That Improve the Performance of Greenhouse-Grown Petunias under Low Fertility Conditions

The production of greenhouse ornamentals relies on high fertilizer inputs to meet scheduling deadlines and quality standards, but overfertilization has negative environmental impacts. The goals of this study were to identify plant-growth-promoting rhizobacteria (PGPR) that can improve greenhouse ornamental crop performance with reduced fertilizer inputs, and to identify the best measurements of plant performance for assessing the beneficial impact of PGPR on ornamentals. A high-throughput greenhouse trial was used to identify 14 PGPR isolates that improved the flower/bud number and shoot dry weight of Petunia × hybrida ‘Picobella Blue’ grown under low fertility conditions in peat-based media. These 14 PGPR were then applied to petunias grown under low fertility conditions (25 mg L⁻¹ N). PGPR-treated plants were compared to negative (untreated at 25 mg L⁻¹ N) and positive (untreated at 50, 75, 100, and 150 mg L⁻¹ N) controls. Multiple parameters were measured in the categories of flowering, vegetative growth, and vegetative quality to determine the best measurements to assess improvements in ornamental plant performance. Caballeronia zhejiangensis C7B12-treated plants performed better in almost all parameters and were comparable to untreated plants fertilized with 50 mg L⁻¹ N. Genomic analysis identified genes that were potentially involved in plant growth promotion. Our study identified potential PGPR that can be used as biostimulants to produce high-quality greenhouse ornamentals with lower fertilizer inputs.

Invasive Lactuca serriola seeds contain endophytic bacteria that contribute to drought tolerance

The mutualistic relationship between alien plant species and microorganisms is proposed to facilitate or hinder invasive success, depending on whether plants can form novel associations with microorganisms in the introduced habitats. However, this hypothesis has not considered seed endophytes that would move together with plant propagules. Little information is available on the seed endophytic bacteria of invasive species and their effects on plant performance. We isolated the seed endophytic bacteria of a xerophytic invasive plant, Lactuca serriola, and examined their plant growth-promoting traits. In addition, we assessed whether these seed endophytes contributed to plant drought tolerance. Forty-two bacterial species were isolated from seeds, and all of them exhibited at least one plant growth-promoting trait. Kosakonia cowanii occurred in all four tested plant populations and produced a high concentration of exopolysaccharides in media with a highly negative water potential. Notably, applying K. cowanii GG1 to Arabidopsis thaliana stimulated plant growth under drought conditions. It also reduced soil water loss under drought conditions, suggesting bacterial production of exopolysaccharides might contribute to the maintenance of soil water content. These results imply that invasive plants can disperse along with beneficial bacterial symbionts, which potentially improve plant fitness and help to establish alien plant species.

Microbial Diversity of Psychrotolerant Bacteria Isolated from Wild Flora of Andes Mountains and Patagonia of Chile towards the Selection of Plant Growth-Promoting Bacterial Consortia to Alleviate Cold Stress in Plants

Cold stress decreases the growth and productivity of agricultural crops. Psychrotolerant plant growth-promoting bacteria (PGPB) may protect and promote plant growth at low temperatures. The aims of this study were to isolate and characterize psychrotolerant PGPB from wild flora of Andes Mountains and Patagonia of Chile and to formulate PGPB consortia. Psychrotolerant strains were isolated from 11 wild plants (rhizosphere and phyllosphere) during winter of 2015. For the first time, bacteria associated with Calycera, Orites, and Chusquea plant genera were reported. More than 50% of the 130 isolates showed ≥33% bacterial cell survival at temperatures below zero. Seventy strains of Pseudomonas, Curtobacterium, Janthinobacterium, Stenotrophomonas, Serratia, Brevundimonas, Xanthomonas, Frondihabitans, Arthrobacter, Pseudarthrobacter, Paenarthrobacter, Brachybacterium, Clavibacter, Sporosarcina, Bacillus, Solibacillus, Flavobacterium, and Pedobacter genera were identified by 16S rRNA gene sequence analyses. Ten strains were selected based on psychrotolerance, auxin production, phosphate solubilization, presence of nifH (nitrogenase reductase) and acdS (1-aminocyclopropane-1-carboxylate (ACC) deaminase) genes, and anti-phytopathogenic activities. Two of the three bacterial consortia formulated promoted tomato plant growth under normal and cold stress conditions. The bacterial consortium composed of Pseudomonas sp. TmR5a & Curtobacterium sp. BmP22c that possesses ACC deaminase and ice recrystallization inhibition activities is a promising candidate for future cold stress studies.

Dynamic Changes in the Microbiome of Rice During Shoot and Root Growth Derived From Seeds

Microbes form close associations with host plants including rice as both surface (epiphytes) and internal (endophytes) inhabitants. Yet despite rice being one of the most important cereal crops agriculturally and economically, knowledge of its microbiome, particularly core inhabitants and any functional properties bestowed is limited. In this study, the microbiome in rice seedlings derived directly from seeds was identified, characterized and compared to the microbiome of the seed. Rice seeds were sourced from two different locations in Arkansas, USA of two different rice genotypes (Katy, M202) from two different harvest years (2013, 2014). Seeds were planted in sterile media and bacterial as well as fungal communities were identified through 16S and ITS sequencing, respectively, for four seedling compartments (root surface, root endosphere, shoot surface, shoot endosphere). Overall, 966 bacterial and 280 fungal ASVs were found in seedlings. Greater abundance and diversity were detected for the microbiome associated with roots compared to shoots and with more epiphytes than endophytes. The seedling compartments were the driving factor for microbial community composition rather than other factors such as rice genotype, location and harvest year. Comparison with datasets from seeds revealed that 91 (out of 296) bacterial and 11 (out of 341) fungal ASVs were shared with seedlings with the majority being retained within root tissues. Core bacterial and fungal microbiome shared across seedling samples were identified. Core bacteria genera identified in this study such as Rhizobium, Pantoea, Sphingomonas, and Paenibacillus have been reported as plant growth promoting bacteria while core fungi such as Pleosporales, Alternaria and Occultifur have potential as biocontrol agents.

Complete Genome Sequence of Pantoea ananatis Strain NN08200, an Endophytic Bacterium Isolated from Sugarcane

Stain NN08200 was isolated from the surface-sterilized stem of sugarcane grown in Guangxi province of China. The stain was Gram-negative, facultative anaerobic, non-spore-forming bacteria. The complete genome SNP-based phylogenetic analysis indicate that NN08200 is a member of the genus Pantoea ananatis. Here, we summarize the features of strain NN08200 and describe its complete genome. The genome contains a chromosome and two plasmids, in total 5,176,640 nucleotides with 54.76% GC content. The chromosome genome contains 4598 protein-coding genes, and 135 ncRNA genes, including 22 rRNA genes, 78 tRNA genes and 35 sRNA genes, the plasmid 1 contains 149 protein-coding genes and the plasmid 2 contains 308 protein-coding genes. We identified 130 tandem repeats, 101 transposon genes, and 16 predicted genomic islands on the chromosome. We found an indole pyruvate decarboxylase encoding gene which involved in the biosynthesis of the plant hormone indole-3-acetic acid, it may explain the reason why NN08200 stain have growth-promoting effects on sugarcane. Considering the pathogenic potential and its versatility of the species of the genus Pantoea, the genome information of the strain NN08200 give us a chance to determine the genetic background of interactions between endophytic enterobacteria and plants.

Facing Climate Change: Application of Microbial Biostimulants to Mitigate Stress in Horticultural Crops

In the current scenario of rapidly evolving climate change, crop plants are more frequently subjected to stresses of both abiotic and biotic origin, including exposure to unpredictable and extreme climatic events, changes in plant physiology, growing season and phytosanitary hazard, and increased losses up to 30% and 50% in global agricultural productions. Plants coevolved with microbial symbionts, which are involved in major functions both at the ecosystem and plant level. The use of microbial biostimulants, by exploiting this symbiotic interaction, represents a sustainable strategy to increase plant performances and productivity, even under stresses due to climate changes. Microbial biostimulants include beneficial fungi, yeasts and eubacteria sharing the ability to improve plant nutrition, growth, productivity and stress tolerance. This work reports the current knowledge on microbial biostimulants and provides a critical review on their possible use to mitigate the biotic and abiotic stresses caused by climate changes. Currently, available products often provide a general amelioration of cultural conditions, but their action mechanisms are largely undetermined and their effects often unreliable. Future research may lead to more specifically targeted products, based on the characterization of plant-microbe and microbial community interactions.

Synergisms of Microbial Consortia, N Forms, and Micronutrients Alleviate Oxidative Damage and Stimulate Hormonal Cold Stress Adaptations in Maize

AIMS

Low soil temperature in spring is a major constraint for the cultivation of tropical crops in temperate climates. This study aims at the exploitation of synergistic interactions of micronutrients, consortia of plant growth-promoting microorganisms and N forms as cold-stress protectants.

METHODS

Maize seedlings were exposed for two weeks to low root zone temperatures at 8-14°C under controlled conditions on a silty clay-loam soil (pH 6.9) collected from a maize field cultivation site. A pre-selection trial with fungal and bacterial PGPM strains revealed superior cold-protective performance for a microbial consortium of Trichoderma harzianum OMG16 and Bacillus spp. with Zn/Mn supplementation (CombiA+), particularly in combination with N-ammonium as a starting point for the characterization of the underlying physiological and molecular mechanisms.

RESULTS

In nitrate-treated plants, the cold stress treatment increased oxidative leaf damage by 133% and reduced the shoot biomass by 25%, related with reduced acquisition of phosphate (P), zinc (Zn) and manganese (Mn). The supplying of N as ammonium improved the Zn and Mn nutritional status and increased the ABA shoot concentration by 33%, as well as moderately increased detoxification of reactive oxygen species (ROS). Moreover, use of N as ammonium also increased the root auxin (IAA) concentration (+76%), with increased expression of auxin-responsive genes, involved in IAA synthesis (ZmTSA), transport (ZmPIN1a), and perception (ZmARF12). Additional inoculation with the microbial consortium promoted root colonization with the inoculant strain T. harzianum OMG16 in combination with ammonium fertilization (+140%). An increased ABA/cytokinin ratio and increased concentrations of jasmonic (JA) and salicylic acids (SA) were related to a further increase in enzymatic and non-enzymatic ROS detoxification. Additional supplementation with Zn and Mn further increased shoot IAA, root length and total antioxidants, resulting in the highest shoot biomass production and the lowest leaf damage by oxidative chemical species.

CONCLUSION

Our results suggest the mitigation of cold stress and reduction of stress priming effects on maize plants due to improved ROS detoxification and induction of hormonal stress adaptations relying on the strategic combination of stress-protective nutrients with selected microbial inoculants.

Draft genome sequence of a cold-adapted phosphorous-solubilizing Pseudomonas koreensis P2 isolated from Sela Lake, India

The draft genome sequence of a cold-adapted phosphorus-solubilizing strain Pseudomonas koreensis P2 isolated from the Sela Lake contains 6,436,246 bp with G + C content of 59.8%. The genome sequence includes 5743 protein coding genes, 68 non-protein coding genes, 1007 putative proteins, 5 rRNA genes, 64 tRNAs and two prophage regions in 40 contigs. Besides these, genes involved in phosphate solubilization, siderophore production, iron uptake, heat shock and cold shock tolerance, multidrug resistance and glycine-betaine production were also identified.

Desert plant bacteria reveal host influence and beneficial plant growth properties

Deserts, such as those found in Saudi Arabia, are one of the most hostile places for plant growth. However, desert plants are able to impact their surrounding microbial community and select beneficial microbes that promote their growth under these extreme conditions. In this study, we examined the soil, rhizosphere and endosphere bacterial communities of four native desert plants Tribulus terrestris, Zygophyllum simplex, Panicum turgidum and Euphorbia granulata from the Southwest (Jizan region), two of which were also found in the Midwest (Al Wahbah area) of Saudi Arabia. While the rhizosphere bacterial community mostly resembled that of the highly different surrounding soils, the endosphere composition was strongly correlated with its host plant phylogeny. In order to assess whether any of the native bacterial endophytes might have a role in plant growth under extreme conditions, we analyzed the properties of 116 cultured bacterial isolates that represent members of the phyla Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. Our analysis shows that different strains have highly different biochemical properties with respect to nutrient acquisition, hormone production and growth under stress conditions. More importantly, eleven of the isolated strains could confer salinity stress tolerance to the experimental model plant Arabidopsis thaliana suggesting some of these plant-associated bacteria might be useful for improving crop desert agriculture.

Bioprospecting cold-adapted plant growth promoting microorganisms from mountain environments

Mountain soils are challenging environments for all kinds of living things, including plants and microorganisms. Many cold-adapted microorganisms colonizing these extreme soils play important roles as promoters of plant growth and development; for that reason, they are called collectively plant growth-promoting microorganisms (PGPM). Even though there is seldom doubt concerning the usefulness of PGPM to develop eco-friendly bioinoculants, including biofertilizers and biocontrollers, a series of aspects need to be addressed in order to make this technology field-applicable. Among these aspects, the ecological and rhizosphere competences of PGPM are of paramount importance, particularly when considering the development of bioinoculants, well suited for the intensification of mountainous agricultural production. Studies on native, cold-adapted PGPM conducted in the Indian Himalayan region (IHR) and the Tropical Andes (TA) lead nowadays the research in this field. Noticeably, some common themes are emerging. For instance, soils in these mountain environments are colonized by many cold-adapted PGPM able to mobilize soil nutrients and to inhibit growth of plant pathogens. Studies aimed at deeply characterizing the abilities of such PGPM is likely to substantially contribute towards a better crop productivity in mountainous environments. The present review focuses on the importance of this microbial resource to improve crop productivity in IHR and TA. We also present a number of successful examples, which emphasize the effectiveness of some bioinoculants-developed from naturally occurring PGPM-when applied in the field.

Characterization of mineral phosphate solubilizing and plant growth promoting bacteria from termite soil of arid region

Five highly efficient phosphate solubilizing bacteria, viz., Pantoea sp. A3, Pantoea sp. A34, Kosakonia sp. A37, Kosakonia sp. B7 and Bacillus sp. AH9 were isolated from termitorial soils of Sanjivani island of southern Maharashtra, India. These isolates were characterized and explored for phosphate solubilization and plant growth promotion. Among these, Bacillus sp. AH9 showed highest phosphate solubilization index (3.5) and solubilization efficiency (250%) on Pikovskaya agar. Interestingly, Pantoea sp. A34 displayed maximum mineral phosphate solubilization (1072.35 mg/L) in liquid medium and during this period the pH dropped to 3.13. All five isolates had highest P solubilization at 48 h after inoculation. During mineral phosphate solubilization, both gluconic acid and 2-keto gluconic acid were produced by Kosakonia and Bacillus isolates, while only 2-keto gluconic acid was detected in Pantoea isolates. Highest organic acid (39.07 ± 0.04 g/L) production was envisaged in Bacillus sp. AH9, while Pantoea sp. A34 produced the least amount (13.00 ± 0.01 g/L) of organic acid. Seed bacterization with Pantoea sp. A3 and Kosakonia sp. A37 resulted in ~ 37% and ~ 53% increase in root length of tomato seedlings, respectively, while Pantoea sp. A34 and Kosakonia sp. B7 had deleterious effects on root length as well as overall growth of the seedlings. To our knowledge, this is the first report of plant growth promoting potential of microorganisms isolated from termitorial soil of Sanjivani island, which is a drought-prone area. Therefore, such efficient growth promoting P solubilizers can offer an effective solution for sustainable agriculture in arid, dryland farming and drought-prone regions.

Engineering abiotic stress response in plants for biomass production

One of the major challenges in today's agriculture is to achieve enhanced plant growth and biomass even under adverse environmental conditions. Recent advancements in genetics and molecular biology have enabled the identification of a complex signaling network contributing toward plant growth and development on the one hand and abiotic stress response on the other hand. As an outcome of these studies, three major approaches have been identified as having the potential to improve biomass production in plants under abiotic stress conditions. These approaches deal with having changes in the following: (i) plant-microbe interactions; (ii) cell wall biosynthesis; and (iii) phytohormone levels. At the same time, employing functional genomics and genetics-based approaches, a very large number of genes have been identified that play a key role in abiotic stress tolerance. Our Minireview is an attempt to unveil the cross-talk that has just started to emerge between the transcriptional circuitries for biomass production and abiotic stress response. This knowledge may serve as a valuable resource to eventually custom design the crop plants for higher biomass production, in a more sustainable manner, in marginal lands under variable climatic conditions.

Characteristics of two novel cold- and salt-tolerant ammonia-oxidizing bacteria from Liaohe Estuarine Wetland

To achieve a better contaminant removal efficiency in a low-temperature and high-salt environment, two novel strains of cold- and salt-tolerant ammonia-oxidizing bacteria (AOB), i.e., Ochrobactrum sp. (HXN-1) and Aquamicrobium sp. (HXN-2), were isolated from the surface sediment of Liaohe Estuarine Wetland (LEW), China. The optimization of initial ammonia nitrogen concentration, pH, carbon-nitrogen ratio, and petroleum hydrocarbons (PHCs) to improve the ammonia-oxidation capacity of the two bacterial strains was studied. Both bacterial strains showed a high ammonia nitrogen removal rate of over 80% under a high salinity of 10‰. Even at a temperature as low as 15°C, HXN-1 and HXN-2 could achieve an ammonia nitrogen removal rate of 53% and 62%, respectively. The cold- and salt-tolerant AOB in this study demonstrated a high potential for ammonia nitrogen removal from LEW.

Excellent N-fixing and P-solubilizing traits in earthworm gut-isolated bacteria: A vermicompost based assessment with vegetable market waste and rice straw feed mixtures

Vermicomposting is a dependable waste recycling technology which greatly augments N and P levels mainly through microbial action. This paper aims to identify efficient N-fixing (NFB) and P-solubilizing (PSB) bacteria from earthworm intestines. Various combinations of vegetable market waste, rice straw, and cowdung were fed to two earthworm species (Eisenia fetida and Perionyx excavatus). Total organic C decreased, pH shifted towards neutrality, and NPK availability, and microbial (NFB, PSB, and total bacteria) population increased remarkably during vermicomposting with E. fetida. Therefore, 45 NFB and 34 PSB strains isolated from Eisenia gut were initially screened, their inter-dominance assessed, and 8 prolific strains were identified through 16SrRNA sequencing. Interestingly, two novel N-fixing strains of Kluyvera ascorbata emerged as an efficient biofertilizer candidate. Moreover, both N-fixing and P-solubilizing strains of Serratia and Bacillus were isolated from earthworm gut. All the isolated strains significantly improved soil health and facilitated crop growth as compared to commercial biofertilizers.

Cold Stress Tolerance in Psychrotolerant Soil Bacteria and Their Conferred Chilling Resistance in Tomato (Solanum lycopersicum Mill.) under Low Temperatures

The present work aimed to study the culturable diversity of psychrotolerant bacteria persistent in soil under overwintering conditions, evaluate their ability to sustain plant growth and alleviate chilling stress in tomato. Psychrotolerant bacteria were isolated from agricultural field soil samples colleced during winter and then used to study chilling stress alleviation in tomato plants (Solanum lycopersicum cv Mill). Selective isolation after enrichment at 5°C yielded 40 bacterial isolates. Phylogenetic studies indicated their distribution in genera Arthrobacter, Flavimonas, Flavobacterium, Massilia, Pedobacter and Pseudomonas. Strains OS211, OB146, OB155 and OS261 consistently improved germination and plant growth when a chilling stress of 15°C was imposed and therefore were selected for pot experiments. Tomato plants treated with the selected four isolates exhibited significant tolerance to chilling as observed through reduction in membrane damage and activation of antioxidant enzymes along with proline synthesis in the leaves when exposed to chilling temperature conditions (15°C). Psychrotolerant physiology of the isolated bacteria combined with their ability to improve germination, plant growth and induce antioxidant capacity in tomato plants can be employed to protect plants against chilling stress.

Indole-3-acetic acid biosynthetic pathway and aromatic amino acid aminotransferase activities in Pantoea dispersa strain GPK

This investigation deals with the production of IAA by a bacterial isolate Pantoea dispersa strain GPK (PDG) identified by 16S rRNA gene sequence analysis. HPLC and Mass spectral analysis of metabolites from bacterial spent medium revealed that, IAA production by PDG is Trp-dependent and follows indole-3-pyruvic acid (IPyA) pathway. Substrate specificity study of aromatic amino acid aminotransferase (AAT) showed high activities, only when tryptophan (Trp) and α-ketoglutarate (α-kg) were used as substrates. AAT is highly specific for Trp and α-kg as amino group donor and acceptor, respectively. The effect of exogenous IAA on bacterial growth was established. Low concentration of exogenous IAA induced the growth, whereas high concentration decreased the growth of bacterium. PDG treatment significantly increased the root length, shoot length and dry mass of the chickpea and pigeon pea plants.