Endophytic Bacterial Populations Research Articles

Isolation and characterization of non-rhizobial bacteria and arbuscular mycorrhizal fungi from legumes

This study investigates non-rhizobial endophytic bacteria in the root nodules of chickpea (Cicer arietinum L), faba bean (Vicia faba), and cowpea (Vigna unguiculata L. Walp), as well as arbuscular mycorrhizal fungi in the rhizospheric soil of chickpea and faba bean. Out of the 34 endophytic bacterial populations examined, 31 strains were identified as non-rhizobial based on nodulation tests. All strains were assessed for their plant growth-promoting (PGP) activities in vitro. The results revealed that most isolates exhibited multiple PGP activities, such as nitrogen fixation, indole-3-acetic acid (IAA) and ammonia (NH3) production, phosphate solubilization, and exopolysaccharide production. The most effective PGP bacteria were selected for 16S rRNA analysis. Additionally, a total of 36 species of native arbuscular mycorrhizal fungi (AMF) were identified. Acaulospora (100%) and Scutellospora (91.66%) were the most prevalent genera in Cicer arietinum L. and Vicia faba L. plants, respectively. Acaulospora also exhibited the highest spore density and relative abundance in both plants. Moreover, the root colonization of Cicer arietinum L. and Vicia faba L. plants by hyphae, vesicles, and arbuscules (HVA) was significant. The findings of this study provide valuable insights into non-rhizobial endophytic bacteria associated with legume root nodules and the diversity of AMF. These organisms have great potential for PGP and can be manipulated by co-inoculation with rhizobia to enhance their biofertilizer effectiveness. This manipulation is crucial for promoting sustainable agriculture, improving crop growth, and advancing biofertilizer technology.

Distribution and functional perspective analysis of epiphytic and endophytic bacterial communities associated with marine seaweeds, Alexandria shores, Egypt

There is an enormous diversity of life forms present in the extremely intricate marine environment. The growth and development of seaweeds in this particular environment are controlled by the bacteria that settle on their surfaces and generate a diverse range of inorganic and organic chemicals. The purpose of this work was to identify epiphytic and endophytic bacterial populations associated with ten common marine macroalgae from various areas along the Mediterranean Sea coast in Alexandria. This was done to target their distribution and possible functional aspects. Examine the effects of the algal habitat on the counting and phenotypic characterization of bacteria, which involves grouping bacteria based on characteristics such as shape, colour, mucoid nature, type of Gram stain, and their ability to generate spores. Furthermore, studying the physiological traits of the isolates under exploration provides insight into the optimum environmental circumstances for bacteria associated with the formation of algae. The majority of the bacterial isolates exhibited a wide range of enzyme activities, with cellulase, alginase, and caseinase being the most prevalent, according to the data. Nevertheless, 26% of the isolates displayed amylolytic activity, while certain isolates from Miami, Eastern Harbor, and Montaza lacked catalase activity. Geographical variations with the addition of algal extract may impact on the enumeration of the bacterial population, and this might have a relationship with host phylogeny. The most significant observation was that endophytic bacteria associated with green algae increased in all sites, while those associated with red algae increased in Abu Qir and Miami sites and decreased in Eastern Harbor. At the species level, the addition of algal extract led to a ninefold increase in the estimated number of epiphytic bacteria for Cladophora pellucida in Montaza. Notably, after adding algal extract, the number of presented endophytic bacteria associated with Codium sp. increased in Abu Qir while decreasing with the same species in Montaza. In addition to having the most different varieties of algae, Abu Qir has the most different bacterial isolates.

Diversity of endophytic bacteria in two banana cultivars and their potential for plant growth promoter

Abstract. Rahayu T, Purwestri YA, Subandiyah S, Sidiq Y, Widianto D. 2024. Diversity of endophytic bacteria in two banana cultivars and their potential for plant growth promoter. Biodiversitas 25: 2828-2838. The Klutuk banana plant (Musa balbisiana colla) is recognized as a resistant plant against biotic and abiotic stresses. The resistance trait of the cultivar is not exactly revealed but is most likely related to the presence of endophytic bacteria. This study aimed to determine the variation of banana cultivars and their organs on endophytic bacterial populations and their character as plant growth promoters (PGP). The study involved isolating endophytic bacteria from the root, corm, and petiole of cv. Klutuk and cv. Ambon, aged 4-5 months. Isolated endophytic bacteria were evaluated based on plant-growth-promoting (PGP) criteria. Subsequently, 16S rRNA sequences were amplified using 16S primers, 27f and 1492r, then sequenced. The obtained isolates were also identified by comparing the 16S sequences to the NCBI gene bank. The results showed that the population and number of isolates with the most PGP characters were in both banana cultivars' roots, petiole, and corm. Endophytic bacteria with multiple traits as PGP are composed of Phylum Proteobacteria (gamma, alpha, beta), Firmicutes, and Actinobacteria members. Several species are potential as they have multiple PGP traits with high-quantity test results, namely Microbacterium testaceum DSM 20166 strain, Simplicispira sp. CPCC 100842 strain, Klebsiella grimontii SB73 strain, Enterobacter mori LMG 25706 strain, Pantoea sp. CoA11 strain, Agrobacterium tumefaciens IAM 12048, Variovorax guangxiensis GXGD002 strain, Serratia nematodiphila DZ0503SBS1 strain, Bosea thiooxidans BI-42 strain, Erwinia tasmaniensis Et1/99 strain, Methylobacterium fujisawaense DSM 5686 strain, K2 isolate, K8 isolate, and K18 isolates. This study also revealed the endophytic bacterial population and character as plant organs influenced PGP. The roots and petioles became the banana plant organs colonized by endophytic bacteria with multiple traits as PGP. Overall, several isolates were discovered in cv. Klutuk were suspected of being new species with potential as PGP agents, and these were not identified in cv. Ambon.

Isolation and Characterization of Bacterial Endophytes from Maize Genotypes Varying in Resistance against Macrophomina phaseolina

The present work aims to isolate and characterize the bacterial endophytes associated with different maize genotypes varying in resistance to disease reaction against Macrophomina phaseolina. A total of 50 endophytic bacteria were isolated from root and stem of healthy maize plants at 30 DAS, 60 DAS by using two different media like TSA, NA medium and maximum number of endophytic bacterial population were recovered from root followed by stem in all the genotypes and TSA medium was found to be the most suitable medium for deciphering maximum endophytic bacterial diversity. The isolated bacterial endophytes were characterized on the basis of morphological parameters viz., size, shape, colour, margin and texture, elevation, gram staining reaction and it was observed that Gram positive bacteria (68.0 %) formed the dominant group. The colony characterization revealed that circular forms (38.0 %) were dominated. Among the colony features the colonies with entire margins (66.0 %) and convex elevation (44.0 %) were found to be dominating.

Deciphering the role of non-Frankia nodular endophytes in alder through in vitro and genomic characterization.

Endophytic bacterial populations are well-positioned to provide benefits to their host plants such as nutrient acquisition and plant hormone level manipulation. Actinorhizal plants such as alders are well known for their microbial symbioses that allow them to colonize harsh environments whether natural or anthropized. Although the nitrogen-fixing actinobacterium Frankia sp. is the main endophyte found in alder root nodules, other bacterial genera, whose roles remain poorly defined, inhabit this niche. In this study, we isolated a diverse panel of non-Frankia nodular endophytes (NFNE). Some NFNE were isolated from alders grown from surface-sterilized seeds and maintained in sterile conditions, suggesting these may have been seed-borne. In vitro testing of 24 NFNE revealed some possessed putative plant growth promotion traits. Their genomes were also sequenced to identify genes related to plant growth promotion traits. This study highlights the complexity of the alder nodular microbial community. It paves the way for further understanding of the biology of nodules and could help improve land reclamation practices that involve alders.

Participation of type VI secretion system in plant colonization of phosphate solubilizing bacteria

In mutualistic endophytic bacteria, the type VI secretion system (T6SS) is related to important functions, such as interbacterial competition, stress response, quorum sensing, biofilm formation, and symbiosis. The presence of T6SS in beneficial endophytic bacterial population associated with different plants suggests that it plays an important role in its interaction with the eucaryotic partner. Within plant promoting bacteria, those with phosphate solubilizing activity constitute a group of great relevance to the rhizosphere as they provide phosphorus to plants. Among them, those with endophytic colonization capacity have survival advantages. The aim of this study was to determine whether the T6SS of a native peanut phosphate solubilizing bacterium is involved in its colonization in this legume. Initially, an in silico analysis looking for genes related to T6SS in the genome of the Enterobacter sp. J49 strain enabled us to identify almost all the tss genes, except for the tssE gene. A T6SS mutant of the Enterobacter sp. J49 strain was obtained by interrupting one of the essential tss genes. Then, the Enterobacter sp. J49-hcp strain was inoculated on peanut plants to analyze its colonization capacity. In addition, properties associated with endophytic colonization were analyzed, such as the formation of biofilms and the production of pectinase and cellulase enzymes. The results obtained indicated a significant decrease in the epiphytic and endophytic colonization of the mutant with respect to the wild strain. It is possible to conclude that T6SS, although not essential, may participate in bacterial colonization, either by accelerating the infection or by promoting other mechanisms involved in it.

Isolation, characterization and evaluation of plant growth promoting activities of bacterial endophytes of tea (Camellia sinensis (L.) O. Kuntze)

In the present study, we are emphasising on isolation, characterization and in vitro evaluation of mineral solubilization and plant growth promoting (PGP) hormone production activities of endophytic bacterial isolates of tea (Camellia sinensis L. (O) Kuntze) root, stem and leaves collected from different tea gardens of upper Assam, India. During the study, it was observed that endophytic bacterial population was highest in roots (ranged between 6.3 x 103-10.3 x 103cfu/ml) followed by stem (ranged between 5.6 x 102-9.86 x 102cfu/ml) and leaves (ranged between 4.2 x 102-8.6 x 102cfu/ml). Pseudomonas sp. was found to be highest IAA (16.75 ± 0.04 μg/ml) and GA3 producer. Bacillus cereus was found to be highest (174.33 ± 2.0 μg/ml) phosphate solubilizer and Acinetobacter sp. (3.06 ± 0.1) was found to be the most efficient potassium solubilizer among the 40 endophytic bacterial isolates isolated from tea bushes. After in vitro screening of endophytic bacterial isolates for their PGP activities, Bacillus cereus, Bacillus flexus RN 11, Pseudomonas sp. and Pseudomonas rhodesiae were applied in the pot culture experiment to observe their activity in natural condition and were found to be significant in promoting root, stem and leaf growth.

Endophytic Bacteria Pseudomonas aeruginosa PM389 Subsists Host’s (Triticum aestivum) Immune Response for Gaining Entry Inside the Host

The present study was designed to compare the defense response of the host plant towards endophytic bacteria Pseudomonas aeruginosa PM389 and pathogenic bacteria Erwinia carotovora and to correlate the level of defense enzymes vis-a-vis bacterial colonization in the host. Wheat seedlings were treated with 107-108 cells ml-1 endophytic and pathogenic bacteria in the separate experimental set-up, and the level of plant defense enzyme was measured at various time intervals. Comparatively reduced level of most defense enzymes was produced in endophytic bacteria treated plants. While the endophytic bacterial population was almost constant after 24 HAI (hour after inoculation), the population of pathogenic bacteria kept fluctuating during the study period from 24 HAI. Unlike pathogenic bacteria, we observed attenuated defense response in challenged host plants towards endophytic bacteria, which helps endophytes establish inside plant. This study would be useful for understanding the mechanism of colonization and strategies of endophytes to fight against the host defense response.

Endophytic bacterial community diversity in two citrus cultivars with different citrus canker disease resistance.

The selective infection of Xanthomonas citri pv. citri (Xcc) to citrus cultivars is universally known, but the relationship between endophytic bacteria and the resistance of host variety to canker disease remains unclear. In this study, endophytic bacterial populations of two citrus cultivars-the resistant satsuma mandarin and the susceptible Newhall navel orange-were analyzed through high-throughput sequencing. The results showed that endophytic bacterial community of satsuma mandarin was more abundant than that of Newhall navel orange. In addition, bacterial abundance was the highest in the spring samples, followed by that in summer and winter samples, in both the varieties. In all samples, the predominant phyla were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes; the major genera were Bacillus and Stenotrophomonas, and the main species was Bacillus subtilis. According to the analysis of the predominant bacteria in the two citrus cultivars, B. subtilis with potential antagonistic characteristics against Xcc existed universally in all samples. However, the susceptible Newhall navel oranges were abundant in Bacillus subtilis and had a relatively large number of canker-causing cooperative bacteria such as Stenotrophomonas. The results suggested that endophytic bacterial community of the two citrus cultivars had some differences based on the season or plant tissue, and these differences were mainly in the quantity of bacteria, affecting citrus canker disease occurrence. In conclusion, the differences in endophytic bacteria on citrus cultivars might be related to host resistance or susceptibility to citrus canker disease.

Early Pathogen Recognition and Antioxidant System Activation Contributes to Actinidia arguta Tolerance Against Pseudomonas syringae Pathovars actinidiae and actinidifoliorum.

Actinidia chinensis and A. arguta have distinct tolerances to Pseudomonas syringae pv. actinidiae (Psa), but the reasons underlying the inter-specific variation remain unclear. This study aimed to integrate the metabolic and molecular responses of these two kiwifruit species against the highly pathogenic Psa and the less pathogenic P. syringae pv. actinidifoliorum (Pfm) bacterial strains. Disease development was monitored weekly till 21 days post inoculation (dpi), analysing a broad number and variety of parameters including: colony forming units (CFU), foliar symptoms, total chlorophylls, lipid peroxidation, soluble polyphenols, lignin and defense-related gene expression. At the end of the experimental period A. chinensis inoculated with Psa presented the highest endophytic bacterial population, whereas A. arguta inoculated with Pfm showed the lowest values, also resulting in a lower extent of leaf symptoms. Metabolic responses to infection were also more pronounced in A. chinensis with decreased total chlorophylls (up to 55%) and increased lipid peroxidation (up to 53%), compared with non-inoculated plants. Moreover, at 14 dpi soluble polyphenols and lignin concentrations were significantly higher (112 and 26%, respectively) in Psa-inoculated plants than in controls, while in A. arguta no significant changes were observed in those metabolic responses, except for lignin concentration which was, in general, significantly higher in Psa-inoculated plants (by at least 22%), comparing with control and Pfm-inoculated plants. Genes encoding antioxidant enzymes (SOD, APX and CAT) were upregulated at an earlier stage in Psa-inoculated A. arguta than in A. chinensis. In contrast, genes related with phenylpropanoids (LOX1) and ethylene (SAM) pathways were downregulated in A. arguta, but upregulated in A. chinensis in the later phases of infection. Expression of Pto3, responsible for pathogen recognition, occurred 2 dpi in A. arguta, but only 14 dpi in A. chinensis. In conclusion, we found that A. arguta is more tolerant to Psa and Pfm infection than A. chinensis and its primary and secondary metabolism is less impacted. A. arguta higher tolerance seems to be related with early pathogen recognition, the activation of plant antioxidant system, and to the suppression of ET and JA pathways from an earlier moment after infection.

Endophytic Colonization of tomato plants by Gluconacetobacter diazotrophicus and its effect on crops improvement and yield promotion

Gluconacetobacter diazotrophicus (G.d) is a nitrogen-fixing, endophyticand non-nodulating bacterium isolated from sugarcane. The aim of thisstudy was to investigate the effect of different G.d concentrations ontomato plants grown at very low nitrogen levels to examine its ability tocolonize plant tissues and improve crop yield. Tomato seeds wereinoculated with different doses of G.d (109, 1010, and 1011 CFU/ml) andgrown in the glasshouse under nitrogen deficiency conditions. Estimationof endophytic bacterial population was performed by bio-PCRs analysisusing specific primers for G.d. Three months after sowing, significantvariations in the phenotypes and biomass production were observed: theinoculated plants with 1010 and 1011 of G.d-Nfix-3%sucrose showedincreased plant height, root length, nitrogen content, and flower number.They also exhibited a healthier phenotype and higher fruit production incomparison to 109 of G.d-Nfix-3%sucrose and non-inoculated controlplants. These results showed that coating tomato seeds with specificconcentrations of G.d-Nfix-3%sucrose (1010 and 1011 CFU/ml) was aneffective enhancer for crop production at low nitrogen levels and provedthe ability of G.d to enhance production of tomato fruits. In conclusion,this study aimed to develop a natural nitrogen fixing seed coatingtechnology to provide a sustainable solution to fertilizer overuse andnitrogen pollution. This technology is environmentally friendly because itbased on a food-grade bacterium (G.d) derived from sugarcane. It aims toaddress the need of international market for sustainable agriculturalfertilizers. Moreover, it provides a cost benefit to the farmers via reducedfertilizer costs and improved crops yields.

Graphene oxide enters the rice roots and disturbs the endophytic bacterial communities

The environmental release of graphene oxide (GO) will certainly induce the GO exposure to plants. To date, the influence of GO on the intracellular structures and the endophytic bacterial ecology of plants have been rarely reported. In the present study, the rice seedlings were exposed to GO (5mg/L) under hydroponic condition for fifteen days with periodic stir. The cellular structures damage, GO deposition and oxidative stress were found in rice root after GO exposure. A Illumina analysis based on the bacterial 16S rRNA gene showed that the richness, evenness and diversity of endophytic bacterial communities of rice root decreased due to GO exposure. The relative abundance of beneficial endophytic bacterial populations decreased after GO exposure. Out of potential phenotypes predicted by BugBase, the relative abundance of Gram negative, stress-tolerant and biofilm-forming phenotypes, presented an increase trend after GO exposure.

Beneficial Endophytic Bacterial Populations Associated With Medicinal Plant Thymus vulgaris Alleviate Salt Stress and Confer Resistance to Fusarium oxysporum.

As a result of climate change, salinity has become a major abiotic stress that reduces plant growth and crop productivity worldwide. A variety of endophytic bacteria alleviate salt stress; however, their ecology and biotechnological potential has not been fully realized. To address this gap, a collection of 117 endophytic bacteria were isolated from wild populations of the herb Thymus vulgaris in Sheikh Zuweid and Rafah of North Sinai Province, Egypt, and identified based on their 16S rRNA gene sequences. The endophytes were highly diverse, including 17 genera and 30 species. The number of bacterial species obtained from root tissues was higher (n = 18) compared to stem (n = 14) and leaf (n = 11) tissue. The endophytic bacteria exhibited several plant growth-promoting activities in vitro, including auxin synthesis, diazotrophy, phosphate solubilization, siderophore production, and production of lytic enzymes (i.e., chitinase, cellulase, protease, and lipase). Three endophytes representing Bacillus species associated with T. vulgaris such as EGY05, EGY21, and EGY25 were selected based on their ex-situ activities for growth chamber assays to test for their ability to promote the growth of tomato (Solanum lycopersicum L.) under various NaCl concentrations (50–200 mM). All three strains significantly (P < 0.05) promoted the growth of tomato plants under salt stress, compared to uninoculated controls. In addition, inoculated tomato plants by all tested strains decreased (P < 0.05) the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase). Six strains, representing Bacillus and Enterobacter species EGY01, EGY05, EGY16, EGY21, EGY25, and EGY31 were selected based on in vitro antagonistic activity to F. oxysporum for pot experiments under salt stress. All tested strains reduced the disease severity index (DSI) of tomato plants at all tested salt concentrations. Gas-chromatography/mass-spectrometry analysis of cell-free extracts of B. subtilis (EGY16) showed at least ten compounds were known to have antimicrobial activity, with the major peaks being benzene, 1,3-dimethyl-, p-xylene, dibutyl phthalate, bis (2-ethylhexyl) phthalate, and tetracosane. This study demonstrates that diverse endophytes grow in wild thyme populations and that some are able to alleviate salinity stress and inhibit F. oxysporum pathogenesis, making them promising candidates for biofertilizers and biocontrol agents.

Colonization of Arabidopsis thaliana by Herbaspirillum seropedicae promotes its growth and changes its proteomic profile

Herbaspirillum seropedicae is a Plant Growth Promoting Bacterium (PGPB) that colonizes crops of economic interest, especially grasses. Here, we aimed to characterize the association of H. seropedicae with the model dicot Arabidopsis thaliana and its effect on plant growth. The molecular pathways activated during the association were monitored by comparative proteomics. Arabidopsis thaliana seedlings were inoculated with H. seropedicae and grown for 28 days. Plant growth promotion was analyzed by quantifying the total leaf area and the fresh and dry biomass. The endophytic bacterial population was quantified by counts of colony-forming units (CFU), and the bacterial location in plant tissues was determined by epifluorescence microscopy. Changes in the proteomic profile of the plants were investigated by ESI-LC-MS/MS. Herbaspirillum seropedicae colonized the roots of A. thaliana, but was absent from the shoots. The association promoted plant growth significantly. The proteomic analysis revealed several protein groups regulated in the roots and shoots during the association, with an emphasis on the photosynthesis and phenylpropanoid biosynthesis. Herbaspirillum seropedicae colonizes A. thaliana roots and promotes its growth, leading to an increase in biomass and the modulation of specific proteomic responses. These findings open new perspectives into the study of the molecular basis of the positive interaction between H. seropedicae and host plants, both monocots and dicots.

Biohardening of Arabidopsis thaliana Seeds and Seedlings with Fraser Photinia Associated Bacterium (PGB_invit) in In vitro Conditions

The aim of this study was to analyze possible positive effects of putatively endophytic PGPB (PGB_invit), which was isolated from long-term in vitro cultured fraser photinia microshoots, on seed and 7-day old seedling stages of Arabidopsis thaliana. Seeds and in vitro-germinated seedlings were inoculated with 107 CFU/mL and 108 CFU/mL active (A) and inactive (I) endophytic bacterial populations along with their mix compositions (A+I) and suspended in MPYE broth together with their controls (untreated ones). 14 days old seedlings were evaluated for various plant growth parameters [i.e., shoot and root fresh weight (FW), shoot length (SL), shoot and root dry weight (DW), root length (RL) and photosynthetic pigments including chlorophyll a, b and carotenoids of plantlets] as well as endophytic and rhizospheric trait of bacteria. Positive effects of inactive and active bacterium on FW, DW and photosynthetic pigments for 7-day inoculated seedlings were recorded whereas an increase in photosynthetic contents for seed stage inoculations was observed. Rhizospheric and endophytic colonization of the bacteria was confirmed by PCR with the presence of virD1 gene, which is previously recorded to be existed in the plasmid of bacterium after inoculation. Overall, these results demonstrated that this peculiar putative endophytic bacterium being beneficial in active and even more useful in inactive form for A. thaliana when optimum conditions and concentrations are used. Moreover, presence of virD1 gene suggested its potential possibility to be used in bioengineering along with various other beneficial PGPR features as biofertilizer.

Paraburkholderia tropica as a plant-growth–promoting bacterium in barley: characterization of tissues colonization by culture-dependent and -independent techniques for use as an agronomic bioinput

Characterization of barley-tissue–colonization efficiency (Hordeum vulgare L.) by Paraburkholderia tropica MTo-293 after seed inoculation was studied in two plant-growth systems: (1) in flasks with semisolid agar-containing sterile medium, as a suitable environment to study plant-bacteria interaction and also optimize molecular-biology techniques, and (2) in a pot-substrate system as an approach to understand their potential behavior as bioinput. Culture-dependent techniques were implemented to quantify surface and endophytic bacterial populations in plant tissues. Culture-independent techniques were employed to detect and localize the inoculated bacteria in tissue samples along with evaluating the biofilm-forming capability by epifluorescent, confocal-laser-scanning, and scanning-electron microscopy. Plant-growth parameters were measured to evaluate the effects of the inoculated bacteria on the development of the barley plants. Paraburkholderia tropica grew as a biofilm on both abiotic and biotic surfaces and efficiently colonized barley roots and stems in plants grown in flasks in presence of other microorganisms. The bacteria was localized on root surfaces, hairs, and central-cylinder areas. Paraburkholderia tropica also colonized the roots and stems in plants grown in the pot-substrate system. Although no endophytic root colonization occurred, the presence of the inoculated bacteria improved the aerial weight. A nested PCR detected P. tropica in the tissue samples. Paraburkholderia tropica MTo-293 was characterized as an efficient biofilm-forming and barley-tissue–colonizing bacterium despite the presence of other microorganisms, but root endophytic colonization resulted dependent on the plant-growth system. Molecular-biology techniques were optimized, and also, its presence was correlated with plant-growth–promoting activity.

Evaluating the diversity and composition of bacterial communities associated with Vachellia pachyceras - the only existing native tree species in the Kuwait desert.

We investigated the diversity and composition of bacterial communities in rhizospheric and non-rhizospheric bulk soils as well as root nodule bacterial communities of Vachellia pachyceras - the only native tree species existing in the Kuwait desert. Community fingerprinting comparisons and 16S rDNA sequence identifications were used for characterization of the bacterial population using specific primers. The bacterial characterization of soil samples revealed four major phyla: Acidobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. In situ (desert) samples of both rhizospheric and non-rhizospheric bulk soil were dominated by the bacterial phyla Firmicutes and Bacteroidetes, whereas the phylum Betaproteobacteria was present only in non-rhizospheric bulk soil. Ex situ (nursery growing condition) V. pachyceras resulted in restricted bacterial communities dominated by members of a single phylum, Bacteroidetes. Results indicated that the soil organic matter and rhizospheric environments might drive the bacterial community. Despite harsh climatic conditions, data demonstrated that V. pachyceras roots harbor endophytic bacterial populations. Our findings on bacterial community composition and structure have major significance for evaluating how Kuwait's extreme climatic conditions affect bacterial communities. The baseline data obtained in this study will be useful and assist in formulating strategies in ecological restoration programs, including the application of inoculation technologies.

Growth stage and tissue specific colonization of endophytic bacteria having plant growth promoting traits in hybrid and composite maize (Zea mays L.)

Maize, a crop cultivated worldwide, was investigated for plant tissue and crop stage specific colonization of endophytic bacteria. Such bacterial interactions have high potential to enhance maize grain yield by means of biological nitrogen fixation and/or plant growth promoting activities. In this study endophytic bacteria were isolated from a hybrid PEEHM-5 and composite PC-4 maize varieties using root, stem and leaf tissues of plants at vegetative, flowering and maturity stages of growth. PEEHM-5 harbored higher endophytic bacterial population than PC-4 at all growth stages, with highest in roots and at flowering stage. Morphologically 188 different endophytic isolates (82 from PEEHM-5, 106 from PC-4) were screened for plant growth promoting attributes viz. P, K, Zn solubilization, production of hormones, siderophore, ACC deaminase, HCN, biological nitrogen fixation and biocontrol of two maize fungal pathogens. Thirty one potential PGP isolates on RFLP analysis of their amplified 16S rRNA gene, were clustered in 13 phylogenetic groups. On sequencing and blasting of amplified 16S rRNA gene of representative isolates from each group identified PC-4 endophytic bacterial isolates as Bacillus aryabhattai, Pantoea cypripedii, Bacillus licheniformis, Klebsiella sp., Pantoea dispersa, Klebsiella variicola, Pantoea sp., Agrobacterium larrymoorei and PEEHM-5 endophytic bacterial isolates as Bacillus sp., Bacillus amyloliquefaciens, Lactococcus lactis, Bacillus cereus and Staphylococcus hominis. In planta evaluation of potential isolates at variable chemical fertilizer input indicated their potential in compensating nearly 25% of the fertilizer input as observed on their improvement of shoot and root parameters. Lactococcus lactis inoculation influenced maximum followed by Pantoea and Klebsiella isolates.

Evaluation of the Antimicrobial Activity of Endophytic Bacterial Populations From Chinese Traditional Medicinal Plant Licorice and Characterization of the Bioactive Secondary Metabolites Produced by Bacillus atrophaeus Against Verticillium dahliae.

Endophytic bacteria associated with medicinal plants possess unique strategies that enhance growth and suvival of host plants, many of which are mediated by distinctive secondary metabolites. These bacteria and their secondary metabolites are important subjects for both basic and applied research aimed at sustainable agriculture. In the present study, 114 endophytic strains isolated from the wild ethnomedicinal plant Glycyrrhiza uralensis (licorice) were screened for their in vitro antimicrobial activities against common fungal pathogens of tomato (Fusarium oxysporum f. sp., Fulvia fulva, Alternaria solani), cotton (Fusarium oxysporum f. sp. Vesinfectum, Verticillium dahliae), pomegranite (Ceratocystis fimbriata), Cymbidinium (Colletotrichum gloeosporioides), and Tsao-ko (Pestalotiopsis microspora and Fusarium graminearum) and the common bacteria Staphylococcus aureus, Bacillus cereus, Salmonella enteritidis, and Escherichia coli. Several Bacillus strains, particularly Bacillus atrophaeus and Bacillus mojavensis, had a broad spectrum of antifungal and antibacterial activity. A total of 16 strains, selected based on broad antimicrobial activity, were shown to contain at least one putative secondary metabolite-encoding gene (i.e., polyketide synthase or non-ribosomal peptide synthetase) and/or one lytic enzyme (i.e., protease, cellulase, lipase, chitinase), which may be important mediators of antagonistic activity against pathogens. Five strains, representing Bacillus atrophaeus and Bacillus mojavensis, were selected for plant growth chamber experiments based on strong in vitro antifungal activities. All five strains significantly reduced disease severity in Arabidopsis thaliana plants challenged with V. dahlia infection. Gas-chromatography/mass-spectrometry analysis of cell-free extracts of Bacillus atrophaeus strain XEGI50 showed that at least 13 compounds were produced only during co-cultivation with V. dahlia, including putative compounds known to have antimicrobial activity, such as 1,2-benzenedicarboxylic acid, bis (2-methylpropyl) ester; 9,12-octadecadienoic acid (Z,Z)-, methyl ester; 9-octadecenoic acid, methyl ester, (E)-; and decanedioic acid, bis(2-ethylhexyl) ester. To our knowledge, this study is the first to report that bacteria isolated from G. uralensis have biocontrol abilities. Our findings provide new insights into the antimicrobial activities of natural endophytes, particularly B. atrophaeus, and suggest this species may a promising candidate as a biocontrol agent to confer resistance to Verticillium wilt disease and other phytopathogens in cotton and other crops.

Interaction of turmeric (Curcuma longa L.) with beneficial microbes: a review.

Curcuma longa L., commonly known as turmeric, is a rhizomatous herb of the family Zingiberaceae. It is mostly used as a spice, a coloring agent and broadly used in traditional medicine such as Ayurveda, Unani, etc., Turmeric rhizomes interact with a large numbers of rhizosphere-associated microbial species, and some enter the plant tissue and act as endophytes. Both rhizospheric and endophytic species are directly or indirectly involved in growth promotion and disease management in plants and also play an important role in the modulation of morphological growth, secondary metabolite production, curcumin content, antioxidant properties, etc. The present review focuses on the rhizobacterial and endophytic bacterial and fungal populations associated with the turmeric.