Microbe-Responsive Proteomes During Plant-Microbe Interactions Between Rice Genotypes and the Multifunctional Methylobacterium oryzae CBMB20.

BACKGROUND: Rice is colonized by plant growth promoting bacteria such as Methylobacterium leading to mutually beneficial plant-microbe interactions. As modulators of the rice developmental process, Methylobacterium influences seed germination, growth, health, and development. However, little is known about the complex molecular responsive mechanisms modulating microbe-driven rice development. The application of proteomics to rice-microbe interactions helps us elucidate dynamic proteomic responses mediating this association. RESULTS: In this study, a total of 3908 proteins were detected across all treatments of which the non-inoculated IR29 and FL478 share up to 88% similar proteins. However, intrinsic differences appear in IR29 and FL478 as evident in the differentially abundant proteins (DAPs) and their associated gene ontology terms (GO). Successful colonization of M. oryzae CBMB20 in rice resulted to dynamic shifts in proteomes of both IR29 and FL478. The GO terms of DAPs for biological process in IR29 shifts in abundance from response to stimulus, cellular amino acid metabolic process, regulation of biological process and translation to cofactor metabolic process (6.31%), translation (5.41%) and photosynthesis (5.41%). FL478 showed a different shift from translation-related to response to stimulus (9%) and organic acid metabolic acid (8%). Both rice genotypes also showed a diversification of GO terms due to the inoculation of M. oryzae CBMB20. Specific proteins such as peptidyl-prolyl cis-trans isomerase (A2WJU9), thiamine thiazole synthase (A2YM28), and alanine-tRNA ligase (B8B4H5) upregulated in IR29 and FL478 indicate key mechanisms of M. oryzae CBMB20 mediated plant growth promotion in rice. CONCLUSIONS: Interaction of Methylobacterium oryzae CBMB20 to rice results in a dynamic, similar, and plant genotype-specific proteomic changes supporting associated growth and development. The multifaceted CBMB20 expands the gene ontology terms and increases the abundance of proteins associated with photosynthesis, diverse metabolic processes, protein synthesis and cell differentiation and fate potentially attributed to the growth and development of the host plant. The specific proteins and their functional relevance help us understand how CBMB20 mediate growth and development in their host under normal conditions and potentially link subsequent responses when the host plants are exposed to biotic and abiotic stresses.

Inoculation of ACC deaminase-producing endophytic bacteria down-regulates ethylene-induced pathogenesis-related signaling in red pepper (Capsicum annuum L.) under salt stress.

Pathogenesis-related (PR) signaling plays multiple roles in plant development under abiotic and biotic stress conditions and is regulated by a plethora of plant physiological as well as external factors. Here, our study was conducted to evaluate the role of an ACC deaminase-producing endophytic bacteria in regulating ethylene-induced PR signaling in red pepper plants under salt stress. We also evaluated the efficiency of the bacteria in down-regulating the PR signaling for efficient colonization and persistence in the plant endosphere. We used a characteristic endophyte, Methylobacterium oryzae CBMB20 and its ACC deaminase knockdown mutant (acdS- ). The wild-type M. oryzae CBMB20 was able to decrease ethylene emission by 23% compared to the noninoculated and acdS- M. oryzae CBMB20 inoculated plants under salt stress. The increase in ethylene emission resulted in enhanced hydrogen peroxide concentration, phenylalanine ammonia-lyase activity, ß-1,3 glucanase activity, and expression profiles of WRKY, CaPR1, and CaPTI1 genes that are typical salt stress and PR signaling factors. Furthermore, the inoculation of both the bacterial strains had shown induction of PR signaling under normal conditions during the initial inoculation period. However, wild-type M. oryzae CBMB20 was able to down-regulate the ethylene-induced PR signaling under salt stress and enhance plant growth and stress tolerance. Collectively, ACC deaminase-producing endophytic bacteria down-regulate the salt stress-mediated PR signaling in plants by regulating the stress ethylene emission levels and this suggests a new paradigm in efficient colonization and persistence of ACC deaminase-producing endophytic bacteria for better plant growth and productivity.

Development of ACCd producer A. brasilense mutant and the effect of inoculation on red pepper plants.

Azospirillum is a plant-growth-promoting bacterium capable of colonizing and promoting growth in numerous crops of agronomic and horticultural significance. The objective of the present study is to develop Azospirillum brasilense CW903-acdS flocculating cells and to test their performance in promoting the growth of red pepper plants grown under salt stress. The flocculating CW903-acdS recorded 12.6, 37.3 and 91.6% higher ACCd activity at 50, 100 and 150 mM NaCl concentrations, respectively, compared to non-flocculating (normal) CW903-acdS cells. The flocculating CW903-acdS recorded 29.8 and 24.5% higher specific growth rates compared to non-flocculating CW903-acdS cells at 100 and 150 mM NaCl concentration, respectively. The flocculating CW903-acdS recorded 29.7 and 24.5% higher production of IAA-like molecule compared to the non-flocculating CW903-acdS at 100 and 150 mM NaCl concentration, respectively. Similarly, 27.5 and 25.7% higher ARA activity was observed with the flocculating CW903-acdS compared to the non-flocculating CW903-acdS type cells at 100 and 150 mM NaCl concentration, respectively. In the pot culture experiment at 50 and 100 mM NaCl concentration, CW903-acdS inoculated pepper plants recorded 9.4 and 4.7% less ethylene emission, when compared to plants inoculated with non-flocculating CW903-acdS cells. At 100 mM NaCl concentration, plants inoculated with flocculating CW903-acdS recorded 27.5% higher dry weight compared to plants inoculated with non-flocculating CW903-acdS cells. This study implied the significance of flocculating CW903-acdS with better stress amelioration and plant growth promotion in red pepper plants grown under salt-affected conditions due to the positive influence of ACCd activity.

Label-free proteomics approach reveals candidate proteins in rice (Oryza sativa L.) important for ACC deaminase producing bacteria-mediated tolerance against salt stress.

The omics-based studies are important for identifying characteristic proteins in plants to elucidate the mechanism of ACC deaminase producing bacteria-mediated salt tolerance. This study evaluates the changes in the proteome of rice inoculated with ACC deaminase producing bacteria under salt-stress conditions. Salt stress resulted in a significant decrease in photosynthetic pigments, whereas inoculation of Methylobacterium oryzae CBMB20 had significantly increased pigment contents under normal and salt-stress conditions. A total of 76, 51 and 33 differentially abundant proteins (DAPs) were identified in non-inoculated salt-stressed plants, bacteria-inoculated plants under normal and salt stress conditions respectively. The abundances of proteins responsible for ethylene emission and programmed cell death were increased, and that of photosynthesis-related proteins were decreased in non-inoculated plants under salt stress. However, bacteria-inoculated plants had shown higher abundance of antioxidant proteins, RuBisCo and ribosomal proteins that are important for enhancing stress tolerance and improving plant physiological traits. Collectively, salt stress might affect plant physiological traits by impairing photosynthetic machinery and accelerating apoptosis leading to a decline in biomass. However, inoculation of plants with bacteria can assist in enhancing photosynthetic activity, antioxidant activities and ethylene regulation related proteins for attenuating salt-induced apoptosis and sustaining growth and development.

ACC deaminase-producing Brevibacterium linens RS16 enhances heat-stress tolerance of rice (Oryza sativa L.).

The rapid rise in global temperature has adverse effects on rice productivity. The lack of eminent resources for heat stress alleviation is threatening the agricultural sector. Heat stress alleviation by endophytic plant growth-promoting bacteria (PGPB) can be a sustainable and eco-friendly approach. The present study was conducted to check the colonization of Brevibacterium linens RS16 producing ACC (1-aminocyclopropane-1-carboxylate) deaminase in the rice endosphere and to characterize its efficiency in enhancing stress tolerance. The ethylene emission pathway, reactive oxygen species (ROS) concentrations, proline accumulation, expression of glutathione S-transferase (GST), and small heat shock proteins (sHSPs) were monitored at two different levels of heat stress (40°C and 45°C). Bacterial inoculation decreased ethylene emission levels by 26.9% and 24.4% in rice plants exposed to 40°C and 45°C, respectively, compared with the non-inoculated plants. B. linens RS16 also enhanced the expression profiles of glutathione S-transferase. The collective effect of GST expression profiles and decrease in ethylene emission due to bacterial ACC deaminase activity subsequently resulted in a decrease in ROS concentrations. Additionally, HSP16 and HSP26 increased expression in heat-stressed plants inoculated with B. linens RS16 resulted in enhanced stress tolerance (i.e., lesser proline accumulation) than non-inoculated plants. Hence, this study demonstrates the bacteria-mediated tolerance against heat stress by regulating the ethylene emission pathway and upregulating antioxidant enzymes and heat shock proteins.

ACC deaminase and indole acetic acid producing endophytic bacterial co-inoculation improves physiological traits of red pepper (Capsicum annum L.) under salt stress.

Salinity induces myriad of physiological and biochemical perturbations in plants and its amelioration can be attained by the use of potential bacterial synthetic communities. The use of microbial consortia in contrast to single bacterial inoculation can additively enhance stress tolerance and productivity of agricultural crops. In this study, co-inoculation of Pseudomonas koreensis S2CB45 and Microbacterium hydrothermale IC37-36 isolated from arbuscular mycorrhizal fungi (AMF) spore and rice seed endosphere, respectively, were used to evaluate the physiological and biochemical effects on red pepper at two salt concentrations (75 mM and 150 mM). Plant growth promoting characteristics particularly 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, indole acetic acid (IAA) and cytokinin production were higher during co-culturing compared to the individual bacterial culture. The higher ACC deaminase activity had resulted in 20% and 22% decrease in stress ethylene emission compared to the non-inoculated plants at 75 mM and 150 mM salt stress, respectively. The decline in ethylene emission had eventually reduced ROS accumulation, and the co-inoculated plants had also harbored enhanced antioxidant enzyme activities and higher sugar accumulation compared to the other treatments suggesting enhanced tolerance to salinity. Collectively, these results put forward a novel consortium of bacterial strains that can be used for sustainable agricultural practices against salinity.

Plant-microbiome interactions: from community assembly to plant health.

Healthy plants host diverse but taxonomically structured communities of microorganisms, the plant microbiota, that colonize every accessible plant tissue. Plant-associated microbiomes confer fitness advantages to the plant host, including growth promotion, nutrient uptake, stress tolerance and resistance to pathogens. In this Review, we explore how plant microbiome research has unravelled the complex network of genetic, biochemical, physical and metabolic interactions among the plant, the associated microbial communities and the environment. We also discuss how those interactions shape the assembly of plant-associated microbiomes and modulate their beneficial traits, such as nutrient acquisition and plant health, in addition to highlighting knowledge gaps and future directions.

Endomicrobial Community Profiles of Two Different Mealybugs: Paracoccus marginatus and Ferrisia virgata.

Mealybugs (Hemiptera: Coccomorpha: Pseudococcidae) harbour diverse microbial symbionts that play essential roles in host physiology, ecology, and evolution. In this study we aimed to reveal microbial communities associated with two different mealybugs, papaya mealybug (Paracoccus marginatus) and two-tailed mealybug (Ferrisia virgata) collected from the same host plant. Comparative analysis of microbial communities associated with these mealybugs revealed differences that appear to stem from phylogenetic associations and different nutritional requirements. This first report on both bacterial and fungal communities associated with these mealybugs provides a preliminary insight on factors affecting the endomicrobial communities. .

Influence of Brevibacterium linens RS16 on foliage photosynthetic and volatile emission characteristics upon heat stress in Eucalyptus grandis.

Heat stress induces secondary metabolic changes in plants, channeling photosynthetic carbon and energy, away from primary metabolic processes, including, growth. Use of ACC (1-aminocyclopropane-1-carboxylate) deaminase containing plant growth promoting bacteria (PGPB) in conferring heat resistance in plants and the role of PGPB, in altering net carbon assimilation, constitutive and stress volatile emissions has not been studied yet. We exposed leaves of Eucalyptus grandis inoculated and non-inoculated with PGPB Brevibacterium linens RS16 to two levels of heat stress (37 °C and 41 °C for 5 min) and quantified temporal changes in foliage photosynthetic characteristics and volatile emission rates at 0.5 h, day 1 and day 5 after the stress application. Heat stress resulted in immediate reductions in dark-adapted photosystem II (PSII) quantum yield (Fv/Fm), net assimilation rate (A), stomatal conductance to water vapor (gs), and enhancement of stress volatile emissions, including enhanced emissions of green leaf volatiles (GLV), mono- and sesquiterpenes, light weight oxygenated volatile organic compounds (LOC), geranyl-geranyl diphosphate pathway volatiles (GGDP), saturated aldehydes, and benzenoids, with partial recovery by day 5. Changes in stress-induced volatiles were always less in leaves inoculated with B. linens RS16. However, net assimilation rate was enhanced by bacterial inoculation only in the 37 °C treatment and overall reduction of isoprene emissions was observed in bacterially-treated leaves. Principal component analysis (PCA), correlation analysis and partial least squares discriminant analysis (PLS-DA) indicated that different stress applications influenced specific volatile organic compounds. In addition, changes in the expression analysis of heat shock protein 70 gene (DnaK) gene in B. linens RS16 upon exposure to higher temperatures further indicated that B. linens RS16 has developed its own heat resistance mechanism to survive under higher temperature regimes. Taken together, this study demonstrates that foliar application of ACC deaminase containing PGPB can ameliorate heat stress effects in realistic biological settings.

Physiological response of tomato plant to chitosan-immobilized aggregated Methylobacterium oryzae CBMB20 inoculation under salinity stress.

The use of plant growth promoting bacteria as bioinoculant to alleviate salt stress is a sustainable and eco-friendly approach in agriculture. However, the maintenance of the bacterial population in the soil for longer period is a major concern. In the present study, chitosan-immobilized aggregated Methylobacterium oryzae CBMB20 was used as a bioinoculant to improve tomato plant (Solanum lycopersicum Mill.) growth under salt stress. The chitosan-immobilized aggregated M. oryzae CBMB20 was able to enhance plant dry weight, nutrient uptake (N, P, K and Mg2+), photosynthetic efficiency and decrease electrolyte leakage under salt stress conditions. The oxidative stress exerted by elevated levels of salt stress was also alleviated by the formulated bioinoculant, as it up-regulated the antioxidant enzyme activities and enhanced the accumulation of proline which acts as an osmolyte. The chitosan-immobilized aggregated M. oryzae CBMB20 was able to decrease the excess Na+ influx into the plant cells and subsequently decreasing the Na+/K+ ratio to improve tomato plant growth under salt stress conditions. Therefore, it is proposed that the chitosan-immobilized aggregated M. oryzae CBMB20 could be used as a bioinoculant to promote the plant growth under salt stress conditions.

Foliage inoculation by Burkholderia vietnamiensis CBMB40 antagonizes methyl jasmonate-mediated stress in Eucalyptus grandis.

Methyl jasmonate (MeJA) is widely used as a model chemical to study hypersensitive responses to biotic stress impacts in plants. Elevated levels of methyl jasmonate induce jasmonate-dependent defense responses, associated with a decline in primary metabolism and enhancement of secondary metabolism of plants. However, there is no information of how stress resistance of plants, and accordingly the sensitivity to exogenous MeJA can be decreased by endophytic plant growth promoting rhizobacteria (PGPR) harboring ACC (1-aminocyclopropane-1-carboxylate) deaminase. In this study, we estimated stress alleviating potential of endophytic PGPR against MeJA-induced plant perturbations through assessing photosynthetic traits and stress volatile emissions. We used mild (5 mM) to severe (20 mM) MeJA and endophytic plant growth promoting rhizobacteria Burkholderia vietnamiensis CBMB40 and studied how MeJA and B. vietnamiensis treatments influenced temporal changes in photosynthetic characteristics and stress volatile emissions. Separate application of MeJA markedly decreased photosynthetic characteristics and increased lipoxygenase pathway (LOX) volatiles, volatile isoprenoids, saturated aldehydes, lightweight oxygenated compounds (LOC), geranyl-geranyl diphosphate pathway (GGDP) volatiles, and benzenoids. However, MeJA-treated leaves inoculated by endophytic bacteria B. vietnamiensis had substantially increased photosynthetic characteristics and decreased emissions of LOX, volatile isoprenoids and other stress volatiles compared with non-inoculated MeJA treatments, especially at later stages of recovery. In addition, analysis of leaf terpenoid contents demonstrated that several mono- and sesquiterpenes were de novo synthesized upon MeJA and B. vietnamiensis applications. This study demonstrates that foliar application of endophytic bacteria B. vietnamiensis can potentially enhance resistance to biotic stresses and contribute to the maintenance of the integrity of plant metabolic activity.

Impact of Arbuscular Mycorrhizal Fungi on Photosynthesis, Water Status, and Gas Exchange of Plants Under Salt Stress-A Meta-Analysis.

Soil salinization is one of the most serious abiotic stress factors affecting plant productivity through reduction of soil water potential, decreasing the absorptive capacity of the roots for water and nutrients. A weighted meta-analysis was conducted to study the effects of arbuscular mycorrhizal fungi (AMF) inoculation in alleviating salt stress in C3 and C4 plants. We analyzed the salt stress influence on seven independent variables such as chlorophyll, leaf area, photosynthetic rate (Amax), stomatal conductance (Gs), transpiration rate (E), relative water content (RWC), and water use efficiency (WUE) on AMF inoculated plants. Responses were compared between C3 and C4 plants, AMF species, plant functional groups, level of salinity, and environmental conditions. Our results showed that AMF inoculated plants had a positive impact on gas exchange and water status under salt stress. The total chlorophyll contents of C3 plants were higher than C4 plants. However, C3 plants responses regarding Gs, Amax, and E were more positive compared to C4 plants. The increase in G s mainly maintained E and it explains the increase in Amax and increase in E. When the two major AMF species (Rhizophagus intraradices and Funnelliformis mosseae) were considered, the effect sizes of RWC and WUE in R. intraradices were lower than those in F. mosseae indicating that F. mosseae inoculated plants performed better under salt stress. In terms of C3 and C4 plant photosynthetic pathways, the effect size of C4 was lower than C3 plants indicating that AMF inoculation more effectively alleviated salt stress in C3 compared to C4 plants.

Methylobacterium oryzae CBMB20 influences photosynthetic traits, volatile emission and ethylene metabolism in Oryza sativa genotypes grown in salt stress conditions.

MAIN CONCLUSION: Inoculation of endophytic Methylobacterium oryzae CBMB20 in salt-stressed rice plants improves photosynthesis and reduces stress volatile emissions due to mellowing of ethylene-dependent responses and activating vacuolar H+-ATPase. The objective of this study was to analyze the impact of ACC (1-aminocyclopropane-1-carboxylate) deaminase-producing Methylobacterium oryzae CBMB20 in acclimation of plant to salt stress by controlling photosynthetic characteristics and volatile emission in salt-sensitive (IR29) and moderately salt-resistant (FL478) rice (Oryza sativa L.) cultivars. Saline levels of 50 mM and 100 mM NaCl with and without bacteria inoculation were applied, and the temporal changes in stress response and salinity resistance were assessed by monitoring photosynthetic characteristics, ACC accumulation, ACC oxidase activity (ACO), vacuolar H+ ATPase activity, and volatile organic compound (VOC) emissions. Salt stress considerably reduced photosynthetic rate, stomatal conductance, PSII efficiency and vacuolar H+ ATPase activity, but it increased ACC accumulation, ACO activity, green leaf volatiles, mono- and sesquiterpenes, and other stress volatiles. These responses were enhanced with increasing salt stress and time. However, rice cultivars treated with CBMB20 showed improved plant vacuolar H+ ATPase activity, photosynthetic characteristics and decreased ACC accumulation, ACO activity and VOC emission. The bacteria-dependent changes were greater in the IR29 cultivar. These results indicate that decreasing photosynthesis and vacuolar H+ ATPase activity rates and increasing VOC emission rates in response to high-salinity stress were effectively mitigated by M. oryzae CBMB20 inoculation.

Changes in Structural and Functional Responses of Bacterial Communities under Different Levels of Long-Term Compost Application in Paddy Soils.

Soils amended for long-term with high levels of compost demonstrated greater abundance of bacterial members of the phylum Bacteroidetes whereas a decreasing trend in the relative abundance of phylum Acidobacteria was noted with increasing levels of compost. Metabolic profiles predicted by PICRUSt demonstrated differences in functional responses of the bacterial community according to the treatments. Soils amended with lower compost levels were characterized by abundance of genes encoding enzymes contributing to membrane transport and cell growth whereas genes encoding enzymes related to protein folding and transcription were enriched in soils amended with high levels of compost. Thus, the results of the current study provide extensive evidence of the influence of different compost levels on bacterial diversity and community structure in paddy soils.

Interactions between Pseudomonas spp. and their role in improving the red pepper plant growth under salinity stress.

Solitary inoculation of bacteria has been studied widely for plant growth development and amelioration of salinity stress but co-inoculation of bacteria for salt stress amelioration in red pepper plants has been less studied till date. Here, we investigated the co-inoculation effect of Pseudomonas frederiksbergensis OB139 and Pseudomonas vancouverensis OB155 in red pepper plant growth characteristics, plant photosynthesis pigments, ethylene emission, and antioxidant properties under 0, 50, 100 and 150 mM salt stress and compared them with non-inoculated control and single inoculation of each isolate. Results showed increasing concentrations of salinity stress arrested the normal plant growth, increased the stress ethylene levels, disrupted the photosynthetic parameters and also influenced the antioxidant enzymatic activities in non-inoculated control plants. Co-inoculation of 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing Pseudomonas spp. significantly reduced the stress ethylene emission and contributed to a significant increase in plant growth compared to single inoculation and non-inoculated control. Catalase activity which was significantly increased in co-inoculated red pepper plants compared to other treatments imply its ability to efficiently neutralize the hydrogen peroxide ions formed as a result of oxidative stress in plants under salinity stress. Besides, significant reduction in malondialdehyde (MDA) content can be correlated to the increased salt tolerance in co-inoculated red pepper plants. Lastly, the increased content of photosynthetic pigments suggest the importance of co-inoculation in improving photosynthesis of red pepper plants. Together, the data demonstrated the functional compatibility of the ACC deaminase producing bacterial isolates and their role in improving the plant physical and biochemical characteristics under salinity stress.

Conservation and transmission of seed bacterial endophytes across generations following crossbreeding and repeated inbreeding of rice at different geographic locations.

There are comparatively diverse bacterial communities inside seeds, which are vertically transmitted and conserved, becoming sources of endophytes in the next generation of host plants. We studied how rice seed endophyte composition changed over time following crossbreeding, repeated inbreeding, subsequent human selection and planting of different rice seeds in different ecogeographical locations. Using terminal-restriction fragment length polymorphism analysis to study bacterial communities, we observed that diversity between the original parents and their offspring may show significant differences in richness, evenness and diversity indices. Heat maps reveal substantial contributions of both or either parent in the shaping of the bacterial seed endophytes of the offspring. Most of the terminal restriction fragments (T-RFs) of the subsequent progeny could be traced to any or both of its parents while unique T-RFs of the offspring suggest external sources of colonization particularly when the seeds were cultivated in different locations. Many similar groups of endophytic bacteria persist in the seeds even after recultivation in different locations, indicating resilience to environmental changes and conservation of bacteria across generations. This study suggests that parent plants contributed to the shaping of seed bacterial endophytes of their offspring, although it is also possible that these soil grown rice plants recruit similar populations of endophytes from the soil generation after generation. This study also highlights some bacterial groups belonging to Herbaspirillum, Microbacterium, Curtobacterium, Stenotrophomonas, Xanthomonas and Enterobacter that may be part of a transmitted and conserved "core microbiota" that are ubiquitous and dominant members of the endophytic communities of the rice seeds.

Spatial Physiochemical and Metagenomic Analysis of Desert Environment.

Investigating the bacterial diversity and their metabolic capabilities are crucial for interpreting ecological patterns in desert environment, and assessing the presence of exploitable microbial resources. In this study, we evaluated the spatial heterogeneity of physico-chemical parameters, soil bacterial diversity and metabolic adaptation at meter scale. Soil samples were collected from two quadrates a desert environment (Thar Desert, India) which face hot arid climate with very little rainfall and extreme temperatures. Analysis of physico-chemical parameters and subsequent variance analysis (p-values < 0.05) revealed that sulfate, potassium and magnesium ions were the most variable between the quadrates. Microbial diversity of the two quadrates was studied using Illumina bar coded sequencing by targeting V3-V4 regions of 16S rDNA. As the results, 702504 high-quality sequence reads, assigned to 173 operationaltaxonomic units (OTUs) at species level. The most abundant phyla in both quadrates were Actinobacteria (38.72%), Proteobacteria (32.94%), and Acidobacteria (9.24%). At genus level, Gaiellarepresented highest prevalence, followed by Streptomyces, Solirubrobacter, Aciditerrimonas, Geminicoccus, Geodermatophilus, Microvirga, and Rubrobacter. Between the quadrates, significant difference (p-values < 0.05) was found in the abundance of Aciditerrimonas, Geodermatophilus Geminicoccus, Ilumatobacter, Marmoricola, Nakamurella and Solirubrobacter. Metabolic functional mapping revealed diverse biological activities, and was significantly correlated with physico-chemical parameters. The results revealed spatial variation of ions, microbial abundance and functional attributes in the studied quadrates, and patchy nature in local scale. Interestingly, abundance ofthe biotechnologically important phylum Actinobacteria, with large proposition of unclassified speciesin the desert suggested that this arid environment is the promising site for bioprospection.

Brevibacterium linens RS16 confers salt tolerance to Oryza sativa genotypes by regulating antioxidant defense and H+ ATPase activity.

Soil salinity is one of the major limitations that affects both plant and its soil environment, leading to reduced agricultural production. Evaluation of stress severity by plant physical and biochemical characteristics is an established way to study plant-salt stress interaction, but the halotolerant properties of plant growth promoting bacteria (PGPB) along with plant growth promotion is less studied till date. The aim of the present study was to elucidate the strategy, used by ACC deaminase-containing halotolerant Brevibacterium linens RS16 to confer salt stress tolerance in moderately salt-tolerant (FL478) and salt-sensitive (IR29) rice (Oryza sativa L.) cultivars. The plants were exposed to salt stress using 0, 50, and 100 mM of NaCl with and without bacteria. Plant physiological and biochemical characteristics were estimated after 1, 5, 10 days of stress application. H+ ATPase activity and the presence of hydroxyectoine gene (ectD) that is responsible for compatible solute accumulation were also analyzed in bacteria. The height and dry mass of bacteria inoculated plants significantly increased compared to salt-stressed plants, and the differences increased in time dependent manner. Bacteria priming reduced the plant antioxidant enzyme activity, lipid peroxidation and it also regulated the salt accumulation by modulating vacuolar H+ ATPase activity. ATPase activity and presence of hydroxyectoine gene in RS16 might have played a vital role in providing salt tolerance in bacteria inoculated rice cultivars. We conclude that dual benefits provided by the halotolerant plant growth promoting bacteria (PGPB) can provide a major way to improve rice yields in saline soil.