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Oxalic acids are widely distributed in tissues of various plants that can exacerbate the effect on other plant-grazing animals including humans. Bacterial communities had been demonstrated to specify with the rhizosphere of host type and which can differ with oxalogenic plant. The present study has been conducted with the primary objective of understanding the root-associated microbial communities in Colocasia esculenta, an oxalogenic plant and to recognize possible bacterial species that present the potential of having their capability to metabolize oxalates. Of the 852 sequences obtained, 311 corresponded to rhizosphere (S), 250 to rhizoplane (P) and 291 were from non-rhizospheric (NS) soil. Flavobacteriaceae, Enterobacteriaceae, Moraxellaceae and Pseudomonadaceae were the major contributors in the rhizoplane microbial community assemblage. Paenibacillaceae was the major contributor to the rhizospheric microbial community. The findings of the study showed that the rhizoplane, owing to the characteristic root exudates, has a distinctive composition of microbial partners as compared to the rhizosphere and bulk soil communities.

Abiotic stresses such as salt and drought represent adverse environmental conditions that significantly damage plant growth and agricultural productivity. In this study, the mechanism of the plant growth-promoting rhizo-bacteria (PGPR)-stimulated tolerance against abiotic stresses has been explored. Results suggest that PGPR strains, Arthrobacter protophormiae (SA3) and Dietzia natronolimnaea (STR1), can facilitate salt stress tolerance in wheat crop, while Bacillus subtilis (LDR2) can provide tolerance against drought stress in wheat. These PGPR strains enhance photosynthetic efficiency under salt and drought stress conditions. Moreover, all three PGPR strains increase indole-3-acetic acid (IAA) content of wheat under salt and drought stress conditions. The SA3 and LDR2 inoculations counteracted the increase of abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylate (ACC) under both salt and drought stress conditions, whereas STR1 had no significant impact on the ABA and ACC content. The impact of PGPR inoculations on these physiological parameters were further confirmed by gene expression analysis as we observed enhanced levels of the TaCTR1 gene in SA3-, STR1- and LDR2-treated wheat seedlings as compared to uninoculated drought and salt stressed plants. PGPR inoculations enhanced expression of TaDREB2 gene encoding for a transcription factor, which has been shown to be important for improving the tolerance of plants to abiotic stress conditions. Our study suggest that PGPR confer abiotic stress tolerance in wheat by enhancing IAA content, reducing ABA/ACC content, modulating expression of a regulatory component (CTR1) of ethylene signaling pathway and DREB2 transcription factor.

Aims The aim of this study was to determine whether ACC deaminase-containing bacterial treatments could enhance the tolerance of poppy (Papaver somniferum L.) plants against biotic stress of downy mildew caused by Peronospora spp. Methods and Results Three different genotypes of P. somniferum i.e. Sampada, J-16 and I-14 were included in the experiment. The ACC deaminase-containing bacteria Pseudomonas putida (WPTe) reduced the downy mildew disease severity and significantly improved the growth and yield of P. somniferum plants. The chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate were modulated upon WPTe treatments in the poppy plants. We observed reduced synthesis of ethylene precursor (ACC) and abscisic acid (ABA), and enhanced production of indole acetic acid (IAA) in P. somniferum plants upon WPTe treatments. Moreover, WPTe treatment reduced proline and lipid peroxidation in plant leaves. Conclusion These results highlight that the ACC deaminase-containing plant growth promoting rhizobacteria enhance the tolerance of P. somniferum plant against downy mildew. Significance and impact of the study ACC deaminase-containing plant growth promoting rhizobacteria may be used against phytopathogens which apart from protecting the plants from the disease could also be useful in reducing ethylene-induced damages in the event of abiotic stresses. This article is protected by copyright. All rights reserved.

An endophytic species of Micrococcus was isolated from Aloe vera leaf (syn. Aloe barbadensis) and screened for protease production with five other species of Micrococcus. Data indicated that endophytic Micrococcus aloeverae AE-6 MCC 2184T and Micrococcus yunnanensis DSM 21948T showed efficient protease production potential and secreted active protease at high salt (10%), temperature (40 °C) and in wide range of pH 8–10. Unlike M. yunnanensis DSM 21948T, protease production by M. aloeverae AE-6 MCC 2184T was stringently controlled by pH. Protease induction study using different group of peptides, peptide carbohydrates and peptide macronutrient combinations showed variable response with both the organisms. Result indicated that the amount of protease was not directly related to cell biomass but it depends on nature of inducible peptides. In this study we also developed a modified agar-well assay for semi-quantitative data from large number of replicates.

Bacillus aquimaris strain SAMM, a biosurfactant producing moderately halophilic marine bacterium was isolated from Indian Arabian coastline sea water. The strain was found to tolerate up to 2.7 M NaCl indicating osmotic stress sustainable physiological systems. We report here the draft genome sequence of B. aquimaris SAMM, as a candidate bacterium for bioactive surfactant producer. The whole genome sequence with 161 scaffolds, 4,414,932 bp and 44.8% of G+C content for SAMM was obtained using Illumina MiSeq sequencing technology. Annotation was added by the PGAP and RAST prokaryotic genome annotation service and shown 4,247 coding sequences, 123 RNAs genes, classified in 453 subsystems. Several genes encoding enzymatic activities against the high molecular weight polysaccharides, osmotic stress response and siderophore synthesis of potential biotechnological importance were identified in the genome.

The escalating population has amplified the pressure on fertile lands for cultivation of food crops has augmented; therefore, utilization of degraded agricultural fields or wastelands including salt affected soils is a possible alternative for farming of medicinal and aromatic plants. Mentha arvensis L. is grown for its menthol-rich essential oil used in pharmaceutical, cosmetic, flavor, food, beverage and associated industries. The present study is aimed at identifying potential combinations of PGPR and AMF and assesses their potential in improving M. arvensis growth and yield under salt stressed conditions in both controlled and field conditions. Four AM fungi, viz. Glomus aggregatum (Ga), Glomus mosseae (Gm), Glomus fasciculatum (Gf) and Glomus intraradices (Gi) and two PGPR Halomonas desiderata (STR8, GenBank Accession no. JQ436849 ) and Exiguobacterium oxidotolerans (STR36, GenBank Accession no. JQ804988 ) were inoculated in M. arvensis in combination to assess their effects on plant growth and yield under salt stressed conditions through glasshouse trials. The plants applied with G. fasciculatum + E. oxidotolerans (Gf + STR36) recorded highest fresh weights, oil yield as compared to all other treatments as well as control plants in saline conditions. Based on the data obtained in the glasshouse experiments, G. fasciculatum + E. oxidotolerans (Gf + STR36) along with vermicompost were tested for its efficacy in promoting plant growth under naturally occurring salt stressed field conditions. The field trials indicated positive interactive effects of combined application of G. fasciculatum + E. oxidotolerans and vermicompost (Gf + STR36 + VC) as observed through improved plant growth and better AMF colonization. Our results promote the idea of multi-microbial inoculations together with vermicompost as efficient biofertilizers in promoting M. arvensis growth in salt affected fields.

Plant growth promoting microorganisms (rhizospheric bacteria and mycorrhizal fungi) provide a sustainable alternative to enhanced crop production along with improved soil health in varying environments. The present study was aimed to elucidate the alteration occurring in innate rhizospheric microbial communities associated with inoculation of AM fungi and PGPR along with organic manure and the resulting improved plant growth under naturally occurring salt stress. The results demonstrate improved growth of Ocimum basilicum CIM-Saumya plants applied with bio-inoculants (Dietzia natronolimnaea STR1 and Glomus intraradices (Gi)) along with organic manure (vermicompost) under salt stressed soil conditions in both glasshouse and field trials. Rhizospheric microbial (bacteria and fungi) community structure as analyzed through terminal restriction fragment length polymorphism (TRFLP) demonstrated a positive effect of microbial inoculation on the indigenous microbial community structure. A notable impact of combined inoculations on the bacterial community was observed in comparison to single applications of either of the bio-inoculants; however, this effect was not iterated in fungal community structure.

Salinity stress has been recognized as one of the leading causes of land degradation and poor agricultural productivity across the globe. Salt stress negatively impacts plants via generation of reactive oxygen species (ROS) which act as a signal during salt stress simultaneously injuring plant root and shoot tissue by disturbing enzyme, cell wall and membrane function. With the objective of developing sustainable techniques of agriculture in salt affected areas, plant growth promoting rhizobacteria (PGPR) have been employed as growth promoters to study and understand their role in salt stress management in various plants. Recent researches have indicated their participation in ROS management via enhanced enzymatic and nonenzymatic antioxidant activities. ACC deaminase activity present in rhizobacteria has also been credited to manage salinity stress by moderating the levels of increased ethylene in salt affected plants. With the increased focus on environmental friendly approaches of agriculture, the PGPR have become a viable option for enhancing plant yield and productivity; however, the mechanisms driving the plant-microbe communication are still being elucidated.

The higher content of salt in soil is the key constraint to crop productivity. Induction of stress ethylene production from 1-aminocyclopropane-1-carboxylate (ACC) in the plant system is one of the consequences of salt stress responsible for toxicity to the plant. Several transgenic plants have been developed by expressing the ACC deaminase bacterial gene as a stress management strategy which apart from being a costly proposition lacks public acceptability. Our main objective was to investigate if a plant inoculated with ACC-deaminase-producing bacterial endophyte will effectively mitigate salt-induced damage and act as an alternative to transgenics. An ACC deaminase-producing salt-tolerant endophyte SMR20 (Brachybacterium paraconglomeratum) was isolated from the roots of Chlorophytum borivilianum, a medicinal plant sensitive to salt stress. Initially we tested ACC-deaminase-producing SMR20 for amelioration of salt stress-induced damage at three different concentrations of salt, that is, 0, 75, 100 and 150 mM NaCl. 150 mM salt stress was selected for further study because wider differences between inoculated and uninoculated plants were noticed under this concentration of NaCl stress. Inoculated with SMR20 successfully protected C. borivilianum from salt stress-induced crop losses. SMR20 significantly alleviated the negative impact of salinity by potential deamination of ACC (precursor for ethylene generation) in the host Chlorophytum roots leading to decreased production of stress ethylene, delayed chlorosis and senescence that resulted in improved yield of plants. Apart from reducing stress ethylene, the presence of the endophyte also affected other phytohormone quantities like indole-3-acetic acid and abscisic acid in plants. It also altered the amount of total leaf pigments and biochemical compounds like proline, malondialdehyde and enhanced foliar nutrient uptake. Due to these outcomes, it appears that an ACC-deaminase-producing endophyte can enhance crop tolerance against salinity stress and can be an important area to explore.

The resilience of soil microbial populations and processes to environmental perturbation is of increasing interest as alteration in rhizosphere microbial community dynamics impacts the combined functions of plant-microbe interactions. The present study was conducted to investigate the effect of inoculation with halotolerant rhizobacteria Bacillus pumilus (STR2), Halomonas desiderata (STR8), and Exiguobacterium oxidotolerans (STR36) on the indigenous root-associated microbial (bacterial and fungal) communities in maize under non-saline and salinity stress. Plants inoculated with halotolerant rhizobacteria recorded improved growth as illustrated by significantly higher shoot and root dry weight and elongation in comparison to un-inoculated control plants under both non-saline and saline conditions. Additive main effect and multiplicative interaction ordination analysis revealed that plant growth promoting rhizobacteria (PGPR) inoculations as well as salinity are major drivers of microbial community shift in maize rhizosphere. Salinity negatively impacts microbial community as analysed through diversity indices; among the PGPR-inoculated plants, STR2-inoculated plants recorded higher values of diversity indices. As observed in the terminal-restriction fragment length polymorphism analysis, the inoculation of halotolerant rhizobacteria prevents major shift of the microbial community structure, thus enhancing the resilience capacity of the microbial communities.

Induction of stress ethylene production in the plant system is one of the consequences of salt stress which apart from being toxic to the plant also inhibits mycorrhizal colonization and rhizobial nodulation by oxidative damage. Tolerance to salinity in pea plants was assessed by reducing stress ethylene levels through ACC deaminase-containing rhizobacteria Arthrobacter protophormiae (SA3) and promoting plant growth through improved colonization of beneficial microbes like Rhizobium leguminosarum (R) and Glomus mosseae (G). The experiment comprised of treatments with combinations of SA3, G, and R under varying levels of salinity. The drop in plant biomass associated with salinity stress was significantly lesser in SA3 treated plants compared to non-treated plants. The triple interaction of SA3+G+R performed synergistically to induce protective mechanism against salt stress and showed a new perspective of plant-microorganism interaction. This tripartite collaboration increased plant weight by 53%, reduced proline content, lipid peroxidation and increased pigment content under 200 mM salt condition. We detected that decreased ACC oxidase (ACO) activity induced by SA3 and reduced ACC synthase (ACS) activity in AMF (an observation not reported earlier as per our knowledge) inoculated plants simultaneously reduced the ACC content by 60% (responsible for generation of stress ethylene) in SA3+G+R treated plants as compared to uninoculated control plants under 200 mM salt treatment. The results indicated that ACC deaminase-containing SA3 brought a putative protection mechanism (decrease in ACC content) under salt stress, apart from alleviating ethylene-induced damage, by enhancing nodulation and AMF colonization in the plants resulting in improved nutrient uptake and plant growth.

This study was aimed to investigate the effect of inoculation on three salt-tolerant, plant-growth-promoting rhizobacteria (PGPR) STR2 (Bacilluspumilus), STR8 (Halomonas desiderata) and STR36 (Exiguobacterium oxidotolerans), for their growth-promoting potential and efficacy in augmenting salt tolerance in Mentha arvensis, an essential oil-bearing crop and natural source of l-menthol, under varying levels of NaCl stress (0, 100, 300 and 500 mM) imposed through irrigating water. Increase in the levels of salt concentration led to a decrease in the growth, fresh weight, leaf–stem ratio, oil content and yield. However, the negative effects of salinity were observed to be convalesced in the PGPR inoculated plants. At salinity levels of 100 and 300 mM NaCl, H. desiderata inoculated plants recorded the highest herb yield, whereas at 500 mM NaCl, the plants inoculated with E. oxidotolerans yielded maximum herb. The oil content in non-inoculated, salt-stressed plants was observed to be 0.46, 0.42 and 0.35 % at 100, 300 and 500 mM NaCl, respectively, whereas the plants inoculated with H. desiderata recorded the oil content of 0.71 and 0.60 and 0.48 % at similar levels of NaCl stress, respectively. The halotolerant PGPR minimized the deleterious effects of salt toxicity producing at par or higher yields at lower and medium salinity levels (100, 300 mM NaCl) than the un-inoculated non-salt-stressed plants through improved foliar nutrient uptake and enhanced antioxidant machinery. Based on the results of the experiments reported herein, the use of salt-tolerant, plant-growth-promoting bacteria may provide an effective means of facilitating M. arvensis growth in salt-stressed environments.

This study was aimed at protecting Trigonella plants by reducing stress ethylene levels through ACC (1-aminocyclopropane-1-carboxylic acid) deaminase-containing Bacillus subtilis (LDR2) and promoting plant growth through improved colonization of beneficial microbes like Ensifer meliloti (Em) and Rhizophagus irregularis (Ri) under drought stress. A plant growth-promoting rhizobacterium strain possessing high levels of ACC deaminase characterized as B. subtilis was selected. Application of this strain considerably protected Trigonella plants under severe drought stress conditions; this protection was correlated with reduced levels of ACC (responsible for generation of stress ethylene). The experiment consisted of eight inoculation treatments with different combinations of ACC deaminase-containing rhizobacteria LDR2, Ri, and Em under three water regimes. The tripartite combination of LDR2 + Ri + Em acted synergistically to induce protective mechanisms against decreased soil water availability in Trigonella plants and improved plant weight by 56 % with lower ACC concentration (39 % less than stressed noninoculated plants) under severe drought conditions. Drought-induced changes in biochemical markers like reduced chlorophyll concentration, increased proline content, and higher lipid peroxidation were monitored and clearly indicated the protective effects of LDR2 under drought stress. Under drought conditions, apart from alleviating ethylene-induced damage, LDR2 enhanced nodulation and arbuscular mycorrhizal fungi colonization in the plants resulting in improved nutrient uptake and plant growth.

Probiotics are live microbial cells or cultures which promote host growth and vigour. The study of the role of microorganisms in soil and plant health and plant-microbe interactions has been the area of interest for plant pathologists and soil microbiologists since beginning of microbiology. Plant probiotics have garnered a considerable amount of attention due to success of human probiotics in improved human health. Plant probiotics are microorganisms or group of microorganisms which by virtue of their potential role in improved nutrient acquisition and/or biocontrol activities can promote soil health, plant growth and enhance plant tolernace or immunity against various abiotic and biotic stresses. Plant growth-promoting bacteria (PGPBs) are good examples of plant probiotics which augment crop production by different activities like nitrogen fixation, growth hormones production, and phosphorus- and mineral- solubilization, enhancing water and nutrient use efficiency, and act as biocontrol and biopesticides. The growing concern over negative implications of excess use of chemicals in agriculture has led to the search for environmental-friendly alternative plant growth-promoting agents. Plant probiotics (PGPBs) are hence being employed in sustainable agriculture methods across the globe. Although several kinds of biofertilizer and biopesticide formulations are available in the markets and are being used in agricultural practices, their commercial potential is not yet being realized owing to various issues associated with formulations and applications. Therefore, there is a dire need to employ methods and means to enhance the efficacy, safety and shelf-life of the formulations related to plant probiotics. In this chapter, we try to highlight the glitches related with formulations, safety and applications of plant probiotics and also suggest the ways to improve the existing lacunae in formulations and applications of plant probiotics.

Application of Thiosalicylic acid+Bacillus cereus; O-Acetylsalicylic acid+Pseudomonas fluorescens reduced root rot severity by 85 and 88% and enhanced root yields by 358 and 419%, respectively, against Fusarium solani induced root rot disease in Withania somnifera. Reduction in disease severity was correlated with defence-related enzymes peroxidase, polyphenol oxidase and phenyl ammonium lyase.

BACKGROUND Mentha arvensis is cultivated in large parts of the world for its menthol-rich essential oil. The study investigates the potential of four mycorrhizal fungi, viz. Glomus mosseae (Gm), Glomus aggregatum (Ga), Glomus fasciculatum (Gf) and Glomus intraradices (Gi) in alleviating NaCl-induced salt stress in Mentha arvensis cv. Kosi and establishes the specificity of interaction between different mycorrhizal species and their effectiveness in mitigating salt stress in Mentha arvensis. Mycorrhizal and non-mycorrhizal Mentha plants were subjected to NaCl-induced salinity. RESULTS Among the four Glomus species, Gm and Gi reduced salt-induced herb yield losses: a loss of 27.53% and 25.58% respectively under salt stress in comparison to 51.00% in non-mycorrhizal M. arvensis salt-stressed plants. Gm- and Gi-inoculated plants also recorded higher leaf:stem ratio, oil content, and oil yield and menthol concentration in essential oil under both saline and non-saline conditions. CONCLUSION Better performance in terms of herb yield, and oil content and yield was observed in Gi- and Gm-inoculated M. arvensis plants, suggesting the capability of Gi and Gm in protecting plants from the detrimental effects of salt stress; beneficial effects of arbuscular mycorrhizal fungi, however, may vary with host and environment. © 2012 Society of Chemical Industry

Plant growth promoting rhizobacteria (PGPR) hold promising future for sustainable agriculture. Here, we demonstrate a carotenoid producing halotolerant PGPR Dietzia natronolimnaea STR1 protecting wheat plants from salt stress by modulating the transcriptional machinery responsible for salinity tolerance in plants. The expression studies confirmed the involvement of ABA-signalling cascade, as TaABARE and TaOPR1 were upregulated in PGPR inoculated plants leading to induction of TaMYB and TaWRKY expression followed by stimulation of expression of a plethora of stress related genes. Enhanced expression of TaST, a salt stress-induced gene, associated with promoting salinity tolerance was observed in PGPR inoculated plants in comparison to uninoculated control plants. Expression of SOS pathway related genes (SOS1 and SOS4) was modulated in PGPR-applied wheat shoots and root systems. Tissue-specific responses of ion transporters TaNHX1, TaHAK, and TaHKT1, were observed in PGPR-inoculated plants. The enhanced gene expression of various antioxidant enzymes such as APX, MnSOD, CAT, POD, GPX and GR and higher proline content in PGPR-inoculated wheat plants contributed to increased tolerance to salinity stress. Overall, these results indicate that halotolerant PGPR-mediated salinity tolerance is a complex phenomenon that involves modulation of ABA-signalling, SOS pathway, ion transporters and antioxidant machinery.

Brahmi (Bacopa monnieri), an integral component of Indian Ayurvedic medicine system, is facing a threat of extinction owing to the depletion of its natural populations. The present study investigates the prospective of exploitation of halotolerant plant growth promoting rhizobacteria (PGPR) in utilising the salt stressed soils for cultivation of B. monnieri. The effects of two salt tolerant PGPR, Bacillus pumilus (STR2) and Exiguobacterium oxidotolerans (STR36) on the growth and content of bacoside-A, an important pharmaceutical compound in B. monnieri, were investigated under primary and secondary salinity conditions. The herb yields of un-inoculated plants decreased by 48 % under secondary salinization and 60 % under primary salinization than the non salinised plants. Among the rhizobacteria treated plants, E. oxidotolerans recorded 109 and 138 %, higher herb yield than non-inoculated plants subjected to primary and secondary salinity respectively. E. oxidotolerans inoculated plants recorded 36 and 76 % higher bacoside-A content under primary and secondary salinity respectively. Higher levels of proline content and considerably lower levels of lipid peroxidation were noticed when the plants were inoculated with PGPR under all salinity regimes. From the results of this investigation, it can be concluded that, the treatments with salt tolerant PGPR can be a useful strategy in the enhancement of biomass yield and saponin contents in B. monnieri, as besides being an eco-friendly approach; it can also be instrumental in cultivation of B. monnieri in salt stressed environments.

Ocimum sanctum grown as rain-fed crop, is known to be poorly adapted to waterlogged conditions. Many a times the crop suffers extreme damages because of anoxia and excessive ethylene generation due to waterlogging conditions present under heavy rain. The usefulness of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing plant growth promoting rhizobacteria was investigated under waterlogging stress. The comparison of herb yield and stress induced biochemical changes of waterlogged and non-waterlogged plants with and without ACC deaminase-containing microbiological treatments were monitored in this study. Ten plant growth promoting rhizobacteria strains containing ACC-deaminase were isolated and characterized. Four selected isolates Fd2 (Achromobacter xylosoxidans), Bac5 (Serratia ureilytica), Oci9 (Herbaspirillum seropedicae) and Oci13 (Ochrobactrum rhizosphaerae) had the potential to protect Ocimum plants from flood induced damage under waterlogged glass house conditions. Pot experiments were conducted to evaluate the potential of these ACC deaminase-containing selected strains for reducing the yield losses caused by waterlogging conditions. Bacterial treatments protected plants from waterlogging induced detrimental changes like stress ethylene production, reduced chlorophyll concentration, higher lipid peroxidation, proline concentration and reduced foliar nutrient uptake. Fd2 (A. xylosoxidans) induced maximum waterlogging tolerance as treated waterlogged plants recorded maximum growth and herb yield (46.5% higher than uninoculated waterlogged plants) with minimum stress ethylene levels (53% lower ACC concentration as compared to waterlogged plants without bacterial inoculation) whereas under normal non-waterlogged conditions O. rhizosphaerae was most effective in plant growth promotion.

Artemisia annua L. (Asteraceae) is an important medicinal plant whose secondary metabolite artemisinin is used for the treatment of cerebral malaria. A study was undertaken to determine the effect of arbuscular mycorrhizal (AM) fungi, Glomus mosseae, Glomus aggregatum, Glomus fasciculatum, Glomus intraradices and two free living nitrogen fixing bacteria (NFB) (identified as Bacillus subtilis and Stenotrophomonas spp. through 16S rRNA gene sequence analysis), inoculated alone or in combinations on the biomass, nutrient uptake, and content of artemisinin in A. annua under glass house conditions. Various parameters like plant height, total plant biomass, NPK content, leaf yield, mycorrhizal colonization, bacterial population in rhizosphere, phosphatase activity and artemisinin content were determined and found to vary with different treatments. Among all the treatments, plants inoculated with G. mosseae + B. subtilis performed better than any other treatment or uninoculated control plants. The results of the experiment clearly indicated the compatibility and synergy between G. mosseae and B. subtilis and suggested the use of this microbial consortium in A. annua for enhancing growth, biomass yield, and the content and yield of artemisinin.