Plant Growth-promoting Abilities Research Articles

Comparative Study of Heavy Metal Uptake and Analysis of Plant Growth Promotion Potential of Multiple Heavy Metal-Resistant Bacteria Isolated From Arable Land.

Heavy metal-induced pollution is a serious environmental concern. This study was aimed at exploring indigenous heavy metal-resistant and plant growth promoting bacteria from arable land that might be useful for developing green strategies to counter the challenges related to bioremediation and sustainable agriculture. A thorough screening and characterization of all the twenty heavy metal-resistant bacterial isolates obtained in this study was done. Of these, three potent isolates were further analyzed to unravel their heavy metal resistance and uptake potentiality. Minimum inhibitory concentration determination depicted considerable tolerance (≥ 500µg/mL) of the three isolates to Ni, Zn, Fe, Cd, Cu, etc. Growth kinetics of the isolates in presence of various heavy metals indicated differences between normal and metal-induced growth. pH tolerance and pigmentation ability of the isolates were also analyzed. Inductively Coupled Plasma-Mass Spectrometry study revealed maximum Cd uptake by the isolates during exponential phase of growth. One of the isolates demonstrated plant growth promotion ability detected using different in vitro qualitative screening tests. Molecular identification using 16S rRNA depicted the isolates as strains of Pseudomonas aeruginosa. This was the first study of heavy metal-resistant and plant growth promoting bacteria from this region. Further exploration of such multi metal-resistant indigenous bacteria may pave the way for designing effective strategies for bioremediation and sustainable agriculture.

Actinobacteria From Desert: Diversity and Biotechnological Applications.

Deserts, as an unexplored extreme ecosystem, are known to harbor diverse actinobacteria with biotechnological potential. Both multidrug-resistant (MDR) pathogens and environmental issues have sharply raised the emerging demand for functional actinobacteria. From 2000 to 2021, 129 new species have been continuously reported from 35 deserts worldwide. The two largest numbers are of the members of the genera Streptomyces and Geodermatophilus, followed by other functional extremophilic strains such as alkaliphiles, halotolerant species, thermophiles, and psychrotolerant species. Improved isolation strategies for the recovery of culturable and unculturable desert actinobacteria are crucial for the exploration of their diversity and offer a better understanding of their survival mechanisms under extreme environmental stresses. The main bioprospecting processes involve isolation of target actinobacteria on selective media and incubation and selection of representatives from isolation plates for further investigations. Bioactive compounds obtained from desert actinobacteria are being continuously explored for their biotechnological potential, especially in medicine. To date, there are more than 50 novel compounds discovered from these gifted actinobacteria with potential antimicrobial activities, including anti-MDR pathogens and anti-inflammatory, antivirus, antifungal, antiallergic, antibacterial, antitumor, and cytotoxic activities. A range of plant growth-promoting abilities of the desert actinobacteria inspired great interest in their agricultural potential. In addition, several degradative, oxidative, and other functional enzymes from desert strains can be applied in the industry and the environment. This review aims to provide a comprehensive overview of desert environments as a remarkable source of diverse actinobacteria while such rich diversity offers an underexplored resource for biotechnological exploitations.

Changes in Volatile Organic Compounds from Salt-Tolerant Trichoderma and the Biochemical Response and Growth Performance in Saline-Stressed Groundnut

Soil salinity is one of the major obstacles that is limiting the growth and yield of groundnut. This study aims to investigate the effect of growth-promoting fungi, Trichoderma, on groundnut plants that were cultivated in saline conditions. Five different Trichoderma isolates were grown in four different NaCl concentrations. Selected Trichoderma were then applied to the groundnut seeds and their growth and development were monitored during the study. Growth inhibition, volatile organic compounds, chlorophylls, carotenoids, total phenolics and flavonoids, and minerals were assessed between the Trichoderma treatments. Increasing the salt concentration from 0.25–0.75 M decreased the growth of the Trichoderma isolates. The amounts and profiles of the volatile organic compounds from the T. asperellum isolate were significantly different to those in the T. virens isolate. In the vegetative growth stage, increased chlorophyll content was recorded in both the T. asperellum and T. virens-treated groundnut. The leaves that were obtained from the groundnut that was treated with T. virens T.v4 contained significantly higher indole-3-acetic acid (420 µg IAA/g) than the same plants’ roots (113.3 µg IAA/g). Compared to the control groundnut, the T. asperellum T.a8-treated groundnut showed increased phenolics (31%) and flavonoids (43%) and increased shoots and biomass weight at the generative growth stage. This study demonstrates that Trichoderma, with their plant growth promotion ability, could potentially be used to improve the growth of groundnut growing under salinity stress. Importantly, salt-tolerant Trichoderma could be regarded as a beneficial and sustainable way to improve the survival of salt-sensitive crops.

Endophytic Fungi of Salt-Tolerant Plants: Diversity and Ability to Promote Plant Growth.

Suaeda australis, Phragmites australis, Suaeda maritima, Suaeda glauca Bunge, and Limonium tetragonum in the Seocheon salt marsh on the west coast of the Korean Penincula were sampled in order to identify the endophytes inhabiting the roots. A total of 128 endophytic fungal isolates belonging to 31 different genera were identified using the fungal internal transcribed spacer (ITS) regions and the 5.8S ribosomal RNA gene. Fusarium, Paraconiothyrium and Alternaria were the most commonly isolated genera in the plant root samples. Various diversity indicators were used to assess the diversity of the isolated fungi. Pure cultures containing each of the 128 endophytic fungi, respectively, were tested for the plant growth-promoting abilities of the fungus on Waito-C rice germinals. The culture filtrate of the isolate Lt-1-3-3 significantly increased the growth of shoots compared to the shoots treated with the control. Lt-1-3-3 culture filtrate was analyzed and showed the presence of gibberellins (GA1 2.487 ng/ml, GA3 2.592 ng/ml, GA9 3.998, and GA24 6.191 ng/ml). The culture filtrate from the Lt-1-3-3 fungal isolate produced greater amounts of GA9 and GA24 than the wild-type Gibberella fujikuroi, a fungus known to produce large amounts of gibberellins. By the molecular analysis, fungal isolate Lt-1-3-3 was identified as Gibberella intermedia, with 100% similarity.

Effect of Plant-Growth-Promoting Fungi on Eggplant (Solanum melongena L.) in New Reclamation Land

Land reclamation may expand the supply of usable land for food security. Immature soil is not suitable for plant growth and needs to be amended by the addition of organic matter and plant growth-promoting (PGP) microorganisms. However, the effects of different PGP fungi on plant growth in immature soil are largely unexplored. In order to obtain beneficial soil microorganisms with a good PGP ability in new reclamation land, 162 fungal isolates were isolated from different abandoned wastelands, four isolates of which were obtained in this study by the screening of P solubilization, siderophore production, and indole acetic acid (IAA) production. The result of this study revealed that isolate HZ123 had the highest ability to solubilize P and produce siderophores and IAA, followed by HZ23, HZ10, and HZ06. Based on the results of morphological and molecular analyses, isolate HZ06 was identified as Penicillium oxalicum, isolates HZ23 and HZ10 were identified as Aspergillus brunneoviolaceus, and isolate HZ123 was identified as Aspergillustubingensis. Furthermore, the results of in vivo PGP assays demonstrated that isolate HZ123 has a minimal negative effect on the growth of eggplant; however, the other three isolates, particularly isolate HZ06, caused the greatest increase in eggplant biomasses. Overall, these results indicate that isolate HZ06 has great potential as a PGP fungus to develop biofertilizer for application in eggplant production in immature soil from new reclamation land.

Prospecting Endophytic Bacteria Endowed With Plant Growth Promoting Potential Isolated From Camellia sinensis.

Endophytes are well-acknowledged inoculants to promote plant growth, and extensive research has been done in different plants. However, there is a lacuna about the endophytes associated with tea clones and their benefit to promote plant growth. The present study focuses on isolating and characterizing the beneficial endophytic bacteria (EnB) prevalent in commercially important tea clones cultivated in North Eastern India as plant growth promoters. Diversity of culturable EnB microbiome, in vitro traits for plant growth promotion (PGP), and applicability of potent isolates as bioinoculant for in vivo PGP abilities have been assessed in the present study. A total of 106 EnB identified as members of phyla Proteobacteria, Firmicutes, and Actinobacteria were related to 22 different genera and six major clusters. Regarding PGP traits, the percentage of isolates positive for the production of indole acetic acid, phosphate solubilization, nitrogen fixation siderophore, ammonia, and 1-aminocyclopropane-1-carboxylic acid deaminase production were 86.8, 28.3, 78.3, 30.2, 95.3, and 87.7, respectively. In total, 34.0, 52.8, and 17.0% of EnB showed notable production of hydrolytic enzymes like cellulase, protease, and amylase, respectively. Additionally, based on the bonitur score, the top two isolates K96 identified as Stenotrophomonas sp. and M45 identified as Pseudomonas sp. were evaluated for biofilm formation, motility, and in vivo plant growth promoting activity. Results suggested strong biofilm formation and motility in K96 and M45 which may attribute to the colonization of the strains in the plants. Further in vivo plant growth promotion experiment suggested sturdy efficacy of the K96 and M45 as plant growth promoters in nursery condition in commercial tea clones Tocklai vegetative (TV) TV22 and TV26. Thus, this study emphasizes the opportunity of commercialization of the selected isolates for sustainable development of tea and other crops.

Accumulation of beneficial bacteria in the rhizosphere of maize (Zea mays L.) grown in a saline soil in responding to a consortium of plant growth promoting rhizobacteria

PurposeSalt stress reduces plant growth and is now becoming one of the most important factors restricting the agricultural productivity. Inoculation of plant growth-promoting rhizobacteria (PGPR) has been shown to confer plant tolerance against abiotic stress, but the detailed mechanisms of how this occurs remain unclear and the application effects in different reports are unstable. In order to obtain a favorite effect of PGPR inoculation and improve our knowledge about the related mechanism, we performed this study to analyze the mechanism of a PGPR consortium on improving the salt resistance of crops.MethodsA region-specific (Saline land around Bohai Sea in China) PGPR consortium was selected that contains three strains (Pseudomonas sp. P8, Peribacillus sp. P10, and Streptomyces sp. X52) isolated from rhizosphere of Sonchus brachyotus DC. grown in a saline soil. By inoculation tests, their plant growth-promoting (PGP) traits and ability to improve the salt resistance of maize were investigated and shifting in rhizosphere bacterial community of the inoculated plants was analyzed using the high-throughput sequencing technology.ResultsThe three selected strains were salt tolerant, presented several growth promoting properties, and inhibited several phytopathogenic fungi. The inoculation of this consortium promoted the growth of maize plant and enriched the beneficial bacteria in rhizosphere of maize in a saline soil, including the nitrogen fixing bacteria Azotobacter, Sinorhizobium, and Devosia, and the nitrification bacteria Candidatus Nitrososphaera, and Nitrosovibrio.ConclusionsThe bacterial consortium P8/P10/X52 could improve plant growth in a saline soil by both their PGP traits and regulating the rhizosphere bacterial community. The findings provided novel information about how the PGPR helped the plants in the view of microbiome.

Plant growth-promoting abilities and community structure of culturable endophytic bacteria from the fruit of an invasive plant Xanthium italicum.

Diversity of endophytic bacterial communities of capsular fruit, upper and lower seeds of an invasive plant Xanthium italicum growing in Xinjiang, China, was investigated. All isolates from the seed capsules, the upper seeds, and the lower seeds were identified by 16S rRNA gene sequencing, and sequences were compared to bacterial databases to define operational taxonomic units (OTUs). Finally, we obtained 316 endophytic isolates corresponding to 58 OTUs based on 16S rRNA gene sequences. The most common OTU corresponded most closely to Bacillus zhangzhouensis and comprised 9.49% of all bacterial isolates. The richness and diversity of endophytes in lower seeds were higher than that of the upper seeds; moreover, the Chao estimator and Shannon index of endophytes in the lower seeds were approximate to that in the seed capsules. Bacillus and Staphylococcus were found as the common taxa in three different tissues that were investigated (OTUs belong to these genera constituted > 70% of the total community). The bacterial endophytic communities differed significantly among these three fruit tissues, especially Bacillus strains, which have been reported to contribute to plant growth promotion and stress resilience to their hosts in harsh environment; abundance of Bacillus species was in the following order: capsules (78 OTUs) > lower seeds (55 OTUs) > upper seeds (40 OTUs). The lower seeds harboring more Bacillus species might be responsible for their earlier seed germination compared with the upper seeds.

Plant growth-promoting activity of wild-type and bromate-resistant mutant of the endophytic fungus Colletotrichum karstii

Endophytes may play important roles in agriculture. Spontaneous or induced mutant strains may increase their biotechnological properties. Seventeen Colletotrichum endophytic fungi were investigated for their plant growth-promoting characteristics (in vitro phosphate solubilization, IAA, and siderophore production). The five best strains were inoculated into bean seeds, and the most prominent isolate was selected to obtain auxotrophic mutants by Potassium Bromate Resistance System (PBRS). The plant growth-promoting ability of the mutant was also investigated. Further, 41.17% of the evaluated endophytes presented promising results for in vitro assays (C. karstii SL10, C. karstii SL28, C. karstii SL57, C. karstii SL59, C. karstii SL12, C. karstii SL40, and C. karstii SL24). The endophyte C. karstii SL57 was statistically conspicuous for plant height and root length when compared to those in control plants. Bromate-resistant mutant C. karstii SL57 increased in vitro phosphate solubilization (23%) and chlorophyll levels (Chlb 0.607 mg g-1 and Chlt 0.973 mg g-1) of bean plants when compared to the wild-type strain (Chlb 0.551 mg g-1 and Chlt 0.881 mg g-1). This is the first time an auxotrophic mutant fungus has been obtained by PBRS with a biotechnological application for the agricultural field

Genome Mining of Three Plant Growth-Promoting Bacillus Species from Maize Rhizosphere

Bacillus species genomes are rich in plant growth-promoting genetic elements. Bacillus subtilis and Bacillus velezensis are important plant growth promoters; hence, to further improve their abilities, the genetic elements responsible for these traits were characterized and reported. Genetic elements reported include those of auxin, nitrogen fixation, siderophore production, iron acquisition, volatile organic compounds, and antibiotics. Furthermore, the presence of phages and antibiotic-resistant genes in the genomes are reported. Pan-genome analysis was conducted using ten Bacillus species. From the analysis, pan-genome of Bacillus subtilis and Bacillus velezensis are still open. Ultimately, this study brings an insight into the genetic components of the plant growth-promoting abilities of these strains and shows their potential biotechnological applications in agriculture and other relevant sectors.

Evaluation of rhizosphere Streptomyces for zinc solubilizing and plant growth promoting properties

Actinobacteria were isolated from rhizosphere soil and its plant growth-promoting ability was tested. Actinobacteria were screened for promoting plant growth by phosphate and zinc solubilization, gibberellin, siderophore, HCN and indole-3-acetic acid production. The abiotic stresses of all the isolates were tested for parameters such as pH, temperature and NaCl. Upon screening, a potent actinobacteria named Streptomyces sp. ZS-18 was isolated and identified based on the colony characteristics. The potent strain solubilized both the zinc oxide (26 ± 0.75mm) and zinc carbonate (22 ± 0.88mm). The utilization of gibberellic acid (80μg/ml) by the potential strain ZS-18 showed maximum production measured by optical density value of 0.179. The growth of the green gram plant was determined by shoot, root, total length, number of leaves and chlorophyll estimation of the leaves. Streptomyces sp. ZS-18 showed good growth on ISP 1, ISP 2, ISP 3, ISP 5 and ISP 7 medium and moderate growth was observed in ISP 4 and ISP 6 medium. In addition, Actinobacteria were tested for antagonistic activity against plant pathogens. The isolate ZS-18 in the pot trial experiment showed increased growth in comparison with control and cow dung manure.

Evaluation of the PGPR Capacity of Four Bacterial Strains and Their Mixtures, Tested on Lupinus albus var. Dorado Seedlings, for the Bioremediation of Mercury-Polluted Soils

Soil contamination by mercury, which is one of the most toxic heavy metals due to its bioaccumulative capacity, poses a risk to the environment as well as health. The Almadén mining district in Ciudad Real, Spain is one of the most heavily-polluted sites in the world, making the soils unusable. Bioremediation, and more specifically phyto-rhizoremediation, based on the synergistic interaction established between plant and Plant Growth Promoting Rhizobacteria (PGPR), improves the plant’s ability to grow, mobilize, accumulate, and extract contaminants from the soil. The objective of this study is to evaluate the plant growth-promoting ability of four PGPR strains (and mixtures), isolated from the bulk soil and rhizosphere of naturally grown plants in the Almadén mining district, when they are inoculated in emerged seeds of Lupinus albus, var. Dorado in the presence of high concentrations of mercury. After 20 days of incubation and subsequent harvesting of the seedlings, biometric measurements were carried out at the root and aerial levels. The results obtained show that the seeds treatment with PGPR strains improves plants biometry in the presence of mercury. Specifically, strain B2 (Pseudomonas baetica) and B1 (Pseudomonas moraviensis) were those that contributed the most to plant growth, both individually and as part of mixtures (CS5 and CS3). Thus, these are postulated to be good candidates for further in situ phyto-rhizoremediation tests of mercury-contaminated soils.

Co-inoculation with the root endophytic fungus Piriformospora indica and endophytic bacteria improves growth of solanaceous vegetable seedlings

ABSTRACT Application of beneficial rhizobacteria may improve the growth of vegetable transplants and reduce diseases. Plant growth promotion effects of single, and combined, inoculation of the root colonizing endophytic fungus Piriformospora indica and bacterial root endophytes isolated from tomato (Solanum lycopersicum L.), chilli (Capsicum annuum L.), and eggplant (Solanum melongena L.) in seedlings were examined as an initial step for developing microbial inocula for transplant production. The isolates were screened for plant growth promotion ability after seed inoculation. Seedling vigor index was assessed by a roll towel assay followed by evaluation of seedling growth in extruded plastic seedling trays with sterile vermiculite as the planting medium. A compatibility test of bacterial endophytes with P. indica was performed by dual culture plate assay on potato dextrose agar medium. Four isolates from tomato, and 2 each from chilli and eggplant, had compatible reactions with the endophytic fungus. Performance of individual and combined inoculation of the root endophytic fungus and compatible endophytic bacteria in host plants was evaluated. Inoculation with microbial agents improved seedling growth. Combined inoculation of bacterial endophytes and fungal endophyte had no influence on the root colonization pattern of P. indica in tomato, chilli, and eggplant seedlings. Application of both crop-specific endophytic bacteria possessing plant growth promoting ability and root endophytic fungus P. indica improved development of tomato, chilli and eggplant seedlings.

Plant growth-promoting ability and control efficacy of Penicillium aurantiogriseum 44M-3 against sesame Fusarium wilt disease

ABSTRACT Penicillium sp. 44M-3, previously isolated from soil samples in Sanmenxia City (Henan Province, China), was identified as Penicillium aurantiogriseum Dierckx based on sequence analysis of ITS-rDNA, β-tubulin, and calmodulin. In co-culture assays against 14 pathogenic fungi, the inhibition ratios achieved by isolate 44M-3 ranged from 42.90% to 66.0%. Optimising the culture medium conditions to maximise the production of inhibitory substances increased the average inhibitory activity of the filtrate by 44.25% compared to that of the original culture filtrate. Isolate 44M-3 secreted extracellular enzymes such as protease, cellulase, and β-1,3-glucanase on agar plates. Treatment with a spore suspension of isolate 44M-3 significantly reduced the incidence of Sesame Fusarium wilt (P = 0.036) in pot experiments, achieving a maximum control efficacy of 75.88%, which did not differ significantly from carbendazim treatment (P = 0.292). Treatment with isolate 44M-3 spore suspension increased the root length of wheat and dry weight of whole sesame, maize, and tobacco plants, likely due to the isolate’s ability to dissolve insoluble inorganic phosphorus and secrete siderophores and indole acetic acid. Consequently, isolate 44M-3 provides a promising candidate for plant growth promotion and prevention of sesame Fusarium wilt disease.

Taxonomic and functional characteristics of aerobic bacteria isolated from the chloragogenous tissue of the earthworm Aporrectodea molleri

Earthworms are considered as a rich microhabitat for the growth and proliferation of diverse soil microorganisms. Hence, earthworms' associated bacteria attracted interest due to their high metabolic profiles and benefits to soil fertility and plant growth. In this study, we aimed to isolate for the first-time aerobic bacteria present in the chloragogenous tissue of the earthworm Apporectodea molleri and test their Plant Growth-Promoting abilities and their resistance to heavy metals (Mn, Zn, Cu, Cd, and Ni). The 16S rRNA gene sequencing revealed the affiliation of the fifteen isolates to six main bacterial genera: Enterobacter, Citrobacter, Aeromonas, Pseudomonas, Bacillus, Terribacillus. These strains displayed different plant growth promoting traits (e.g., indole-3-acetic acid IAA, siderophores, nitrogen fixation, phosphate, and potassium solubilization), in addition, they were able to resist differently to heavy metals. Bacillus strains were most effective as three strains, namely B. subtilis strain TC34; B. circulans strain TC7 and Bacillus sp. strain TC10, were positive to all PGP traits and resisted to all heavy metals. This study illustrates the potential of bacteria from the chloragogenous tissue to exhibit multiple properties, which can be related to the functional feature of this tissue to stock metabolites and neutralize toxic elements.

Bacterial Inoculants Mitigating Water Scarcity in Tomato: The Importance of Long-Term in vivo Experiments.

Global population growth and climate change raise a challenge to agriculture, which, combined with the issues concerning the use of chemical fertilizers, have generated increasing attention in the use of plant-associated bacteria as a sustainable strategy in agri-food systems. The objective of this study is to evaluate the ability of five bacterial strains, previously isolated from the rhizosphere or endosphere of plants adapted to harsh environmental conditions, to act as potential plant biofertilizers in different conditions of water availability. The strain biosafety for a deliberate environmental release was investigated through a literature survey and antibiotic resistance testing. The selected strains were first characterized for their plant growth–promoting (PGP) and rhizocompetence-related traits through in vitro assays and then on short-term in vivo experiments on tomato plants. A long-term greenhouse experiment was further conducted to monitor the PGP effect of the bacteria during the entire life cycle of tomato plants subjected to full irrigation or to severe water deficit conditions, aiming to assess their actual effect on plant productivity, which is the ultimate target of the agricultural sector. Some of the strains showed a potential in improving water use efficiency and mitigating plant water stress. Under severe irrigation deficit, four of the tested strains, Micrococcus yunnanensis M1, Bacillus simplex RP-26, Pseudomonas stutzeri SR7-77, and Paenarthrobacter nitroguajacolicus 2–50, significantly increased the number of productive plants in comparison to non-bacterized control ones. Two of them, Bacillus simplex RP-26 and Paenarthrobacter nitroguajacolicus 2–50, demonstrated also, under full irrigation, to significantly improve the water productivity in comparison with non-bacterized plants. Despite all the strains showed promising PGP potential in short-term assays, the positive effect of the bacterial inoculants on plant physiology and fruit yield was observed in some cases but never corroborated by statistical significance. These results highlight the importance of performing long-term in vivo experiments to define the real PGP ability of a bacterial inoculant to positively impact plant production.

Isolation and characterization of potassium solubilizing Aspergillus species isolated from saxum habitats and their effect on maize growth in different soil types

Potassium (K) is an important nutrient for plant growth. However, less than 2% of K in the soil exists in plant-available forms. Further, fungi inhabiting saxicolous habitats are infrequently examined for their plant growth-promoting ability. Therefore, in this study, we isolated K solubilizing fungi (KSF) from saxicolous habitats and screened them for their ability to produce plant growth hormones, organic acids, and siderophore that may facilitate plant growth. Seventy-two saxicolous fungal isolates were screened for their K solubilization in Aleksandrow medium amended with mica. Of these, eight potential KSF isolates resembling Aspergillus species based on 18S rRNA gene sequencing were selected for further screening. Three of these KSF isolates KSF-07 (Aspergillus terreus), KSF-55 (Aspergillus niger), and KSF-69 (Aspergillus violaceofuscus) produced different organic acids (ascorbic, acetic, benzoic, citric, malic, and oxalic acid), indole acetic acid (0.678–46.326 µg L−1), and siderophore (46.66–65.26 PSU) under in vitro conditions. The three Aspergillus species solubilized 56.56−59.80 mg L−1 of K from mica and 33.97–39.19 mg L−1 from potassium aluminum silicate. Inoculation of KSF and mica amendment significantly improved plant growth and K uptake by maize and also enhanced the KSF populations in post-harvest soil. Pearson’s correlation analysis revealed the existence of a significant negative correlation between soil pH and available K. Among the KSF isolates screened, A. violaceofuscus (KSF-69) presents an excellent prospect as a bio-inoculant for improving crop growth in different soil types.

The seed-associated microbiome of four cactus species from Southern Chihuahuan Desert

One of the riskiest stages in the reproduction of cactus is the germination of seeds. Although evidence indicates the relevance of the seed-associated microbiome during this stage, little is known about its structure and function. In this work, we explore the diversity of the seed-associated microbiome of cactus, their role in the germination and protection of the emerging embryo. We characterized the microbial communities of the internal tissues (endoseminal) and those that colonize the surface of the seeds (episeminal) of four cactus species (Echinocactus platyacanthus, Ferocactus latispinus, Ferocactus pilosus, and Stenocereus queretaroensis). We sequenced by Illumina the 16S rRNA gene for Bacteria and the ITS1/ITS4 region for fungi. We isolated cultivable microorganisms and characterized their plant growth-promoting abilities. We determined that microbial communities associated with cactus seeds have high richness but are dominated by few taxa, and in most cases, there are clear differences between episeminal and endoseminal microbial groups, especially for fungi. The cactus seed microbiota comprises potential pathogens and beneficial microorganisms that could influence the germination percentage and seedling's development. We can highlight bacterial groups such as Kluyvera, Bacillus, Paenibacillus, and Stenotrophomonas; for fungi, the classes Tremellomycetes, Dothideomycetes, Eurotiomycetes, Leotiomycetes, and Sordariomycetes.

Isolation and characterization of novel plant growth-promoting rhizobacteria (PGPR) isolates from tomato (Solanum lycopersicum L.) rhizospherical soil: A novel IAA producing bacteria

Indole acetic acid (IAA) production is one of the distinctive traits of plant growth-promoting rhizobacteria (PGPR). Ten different rhizobacterial strains were isolated from the roots of tomato crops (Solanum lycopersicum L.), grown in Kuwait, and then screened for their plant growth-promoting abilities, with emphasis on IAA production. The isolated strains were identified by 16S partial r-RNA sequencing and further characterized by conventional biochemical tests. Based on the nucleotide sequence analysis and homology of the isolates, a phylogenetic tree was constructed. The plant growth-promoting abilities of the strains were determined by testing for ammonium production, hydrogen cyanide and acid production, growth in nitrogen-free media, phosphate solubilization, and IAA production. The potential IAA PGPRs were re-applied onto the rhizosphere of green-house grown tomato plants to determine their effects on tomato growth. The results have indicated that all isolated strains were able to produce indole acetic acid even without the presence of a tryptophan precursor.

Diversity of Endophytic Bacteria in Cardamine hupingshanensis and Potential of Culturable Selenium-Resistant Endophytes to Enhance Seed Germination Under Selenate Stress

The endophytic bacterial communities of Se hyperaccumulator Cardamine hupingshanensis collected from greenhouse and seleniummining area in Enshi City were investigated by Illumina sequencing technology. In addition, 14 culturable endophytic selenium-resistant strains were isolated and their selenium tolerance and plant growth promotion abilities were studied. The results showed that phylum Proteobacteria predominated in all the plants (> 70%) regardless of their habitats, with most of the OTUs related to Betaproteobacteria, Alphaproteobacteria, and Gammaproteobacteria. Roots harbored many more OTUs and showed higher alpha diversities than the leaves. Both growing environment and specific microflora selection of plants were found to have noticeable effects on endophytic bacterial community structure. The 14 culturable endophytes belonging to 11 bacterial genera were able to resist different levels of selenite and selenate, with their MIC ranges of 10-120mM and 100-600mM. Among them, Oceanobacillus and Terribacillus genera were firstly reported for the selenium-tolerant properties of their members. Inoculation experiment revealed that three endophytic strains (CHP07, CHP08, and CHP14) with excellent plant growth-promoting traits were beneficial for growth of Brassica chinensis seeds at germination stage under 0.19mM selenate stress.