Effect of Burkholderia sp. KCTC 11096BP on some physiochemical attributes of cucumber

Plant growth promoting rhizobacteria (PGPR) has been a focus of research for its potential as an eco-friendly alternative to chemical fertilizers in the agriculture industry. In current study, the effect of culture suspension (CS) of a novel gibberellins (GAs) producing bacterial strain Burkholderia sp. KCTC 11096BP, was observed on shoot length, shoot fresh and dry biomass, root fresh and dry biomass, chlorophyll contents, endogenous bioactive GAs (GA₁ and GA₄) and their immediate precursors, abscisic acid (ABA), soluble sugar contents and crude protein contents of cucumber (Cucumis sativus L.). We found that growth attributes of cucumber were significantly promoted by the application of CS of Burkholderia sp. KCTC 11096BP. The quantity of GA₁ and GA₄ and their immediate precursors GA₂₀ and GA₉ respectively, were also significantly promoted as compared to their respective controls. Contrary to GAs, the quantity of endogenous free ABA in cucumber leaves was much lower in bacterial CS treated plants. Soluble sugar contents and crude protein contents of cucumber leaves were also significantly higher in bacterial CS treatments as compared to control. It was concluded that Burkholderia sp. KCTC 11096BP can be used as an eco-friendly bio-fertilizer in our farming systems.     

Molybdenum status and critical limit in the soil for green gram (Vigna radiata) growing in Madurai and Sivagangai districts of Tamil Nadu,India

Abstract

The decay of rice residue was investigated after incubation periods of from 1 to 24 months at 30°C under both flooded and upland soil conditions. Tops and roots of rice plants were cut into about 10-mm length, and separately incorporated in soil which had been passed through a 0.5-mm sieve. Plant debris were fractionated physically according to their sizes and divided into five groups (>4 mm, 4-2 mm, 2-1 mm, 1-0.5 mm, and 0.5-0.25 mm).

Carbon loss from the soils amended with rice residues and decrease in the weight of total plant debris proceeded at a rapid speed in the early periods (around 4 months) and then at a slow speed in the subsequent periods under both flooded and uplana soil conditions. The distribution of the plant debris in the decomposition processes differed under flooded and upland conditions. Under flooded conditions, 2–4 mm-sized plant debris were retained for a long period with slow transformation into the smaller fractions. In contrast, under upland conditions, change of plant debris from large to small size fractions proceeded gradually. This continuous change could be attributed to the high decomposing activities of fungi under upland conditions.     

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.     

Endophytic establishment of the soil isolate Burkholderia sp. CC-Al74 enhances growth and P-utilization rate in maize (Zea mays L.)

Bacteria are common inhabitants of the rhizosphere or as endophytes in internal plant tissues. Among many bacterial genera, Burkholderia is a genus rich in nitrogen-fixing and phosphate-solubilizing strains that have been isolated from various plant systems. The function of phosphate-solubilizing bacteria in agriculture has been well documented, including enhancements in growth, yield and disease-resistance of crops. However, their response when introduced into a plant system in vitro is poorly studied. Inoculation of Burkholderia sp. CC-Al74, a phosphate-solubilizing soil isolate, on maize seeds resulted in the persistent endophytic establishment as determined by PCR detection method using Burkholderia-specific 16S rRNA gene primers. Burkholderia sp. CC-Al74-inoculated maize showed significant increases in plant height, plant biomass and root length, of about 45%, 48% and 86%, respectively, as compared to non-inoculated controls. After endophytic establishment, inoculated maize seedlings showed 2.4-fold increase in P-utilization rate in planta as well as an increased rhizosphere phosphatase activity as compared to the non-inoculated control. Nutrient analysis of inoculated maize showed 150% and 90% higher contents of P and N as compared to the non-inoculated control, respectively. Multilocus sequence typing (MLST) analysis showed that Burkholderia sp. CC-Al74 had a unique Sequence-Type, ST-730, which was novel when compared with existing STs in the MLST database. The phylogeny produced by recA sequence and MLST data revealed that Burkholderia sp. CC-Al74 is a novel member of Burkholderia cepacia complex. In summary, we provide direct evidence, which shows that the soil isolate Burkholderia sp. CC-Al74 could improve P-utilization rate as well as total P and N contents post-endophytic colonization in maize in vitro.     

Promotion of mycorrhiza formation and growth of willows by the bacterial strain <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. 23L on fly ash

Re-vegetation of fly ash, the principal by-product of coal fired power stations, is hampered by its unfavourable chemical and physical properties for plant growth. In the present study, we evaluated the use of inoculation with a mycorrhiza-associated bacterial strain (Sphingomonas sp. 23L) to promote mycorrhiza formation and plant growth of three willow clones (Salix spp.) on fly ash from an over-burdened dump in a pot experiment. The high pH_H2O (8.7) and low nitrogen content (N_t = 0.1 g kg⁻¹) in combination with hydrophobicity of the particle surfaces caused low plant growth. Inoculation of the willows with Sphingomonas sp. 23L improved the nitrogen uptake by plants, increased plant growth and stimulated formation of ectomycorrhizae with an autochthonous Geopora sp. strain on all three willow clones. The ectomycorrhiza formed by the Geopora sp. was morphologically and anatomically described. The inoculation significantly increased the shoot growth of two Salix viminalis clones and the root growth of a S. viminalis x caprea hybrid clone. We conclude that inoculation with mycorrhiza promoting bacterial strains might be a suitable approach to support mycorrhiza formation with autochtonous site-adapted ectomycorrhizal fungi in fly ash and thereby to improve re-vegetation of fly ash landfills with willows.     

Synergistic effects of vesicular-arbuscular mycorrhizal fungi and diazotrophic bacteria on nutrition and growth of sweet potato (Ipomoea batatas)

Summary Sweet potatoes were micropropagated and then transplanted from axnic conditions to fumigated soil in pots in the greenhouse. Spores of Glomus clarum were obtained from Brachiaria decumbens or from sweet potatoes grown in soil infected with this fungus and with an enrichment culture of Acetobacter diazotrophicus. Three experiments were carried out to measure the beneficial effects of vesicular-arbuscular mycorrhizal (VAM) fungi-diazotroph interactions on growth, nutrition, and infection of sweet potato by A. diazotrophicus and other diazotrophs obtained from sweet potato roots. In two of these experiments the soils had been mixed with ¹⁵N-containing organic matter. The greatest effects of mycorrhizal inoculation were observed with co-inoculation of A. diazotrophicus and/or mixed cultures of diazotrophs containing A. diazotrophicus and Klebsiella sp. The tuber production was dependent on mycorrhization, and total N and P accumulation were increased when diazotrophs and G. clarum were applied together with VAM fungal spores. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM fungi or when present within G. clarum spores. More pronounced effects on root colonization and intraradical sporulation of G. clarum were observed when A. diazotrophicus was co-inoculated. In non-fumigated soil, dual inoculation effects, however, were of lower magnitude. ¹⁵N analysis of the aerial parts and roots and tubers at the early growth stage (70 days) showed no statistical differences between treatments except for the VAM+Klebsiella sp. treatment. This indicates that the effects of A. diazotrophicus and other diazotrophs on sweet potato growth were caused by enhanced mycorrhization and, consequently, a more efficient assimilation of nutrients from the soil than by N₂ fixation. The possible interactions between these effects are discussed.     

Effect of fungi associated with roots on the growth of continuously cropped upland rice

Pyrenochaeta sp. enriched on and in roots of upland rice through its continuous cropping, was shown to have an ability to inhibit the growth of upland rice in quartz or partially sterilized soil. It was established that the microorganism produced some substance inhibiting the growth of seedlings of upland rice or/in roots of the plant. The results suggested that Pyrenochaeta sp. produced this inhibitor even on/in roots of upland rice continuously cropped on the field, and may play a role in the appearance of upland rice soil sickness.     

Community structure of bacteria and fungi responsible for rice straw decomposition in a paddy field estimated by PCR-RFLP analysis

Rice straw including leaf sheaths and blades put in nylon mesh bags was placed in the plow layer of a Japanese paddy field after harvest under upland conditions and after transplanting of rice seedlings under flooded conditions. In addition, rice straw that was decomposed under the upland conditions during the off-crop season in winter was placed again in soil at the time of transplanting. The materials were collected periodically to analyze the community structure of the bacteria and fungi responsible for rice straw decomposition by PCR-RFLP analysis. The PCR products with 27f and 1492r primers designed for bacterial 16S rDNA and with EF3 and EF4 primers designed for fungal 18S rDNA were digested with four restriction endonucleases (Hinf I, Sau3A I, Hae III, EeoR I). Bacterial communities in the decomposing rice straw were different from each other between upland and flooded conditions, between leaf sheaths and blades, and between straw samples with and without decomposition under upland conditions during the off-crop season. Fungal communities in the decomposing rice straw were also different between the leaf sheaths and blades under upland soil conditions. Score plots of bacterial and fungal communities in the principal component analysis were separated from the plot of the straw materials along with the duration of the placement, indicating the succession of bacterial and fungal communities in decomposing rice straw with time.     

Effect of microcrustaceans on blue-green algae in flooded soil

The ostracod Cypris sp., when present in large numbers, prevented the development of inocula of Tolypothrix tenuis and suppressed inocula of Anabaena sp. added to flooded soil. The waterflea Daphnia magna, when present in large numbers, only had a minor influence on the growth rate or extent of development of these algae. Anabaena sp. was less susceptible than T. tenuis to the two microcrustaceans. It is suggested that grazing by certain microcrustaceans may limit nitrogen fixation by algae in flooded rice fields.     

Tolerance of potentially diazotrophic bacteria to adverse environmental conditions and plant growth-promotion in sugarcane

Sugarcane is one of the crops responsible for the high consumption of fertilizers in Brazil. To minimize this demand a sustainable alternative is to increase the studies to evaluate the beneficial effects of the relationship between plants/microorganisms, mainly plant growth-promoting bacteria. The objectives of this study were: a) to evaluate potentially diazotrophic bacteria isolates from sugarcane in adverse environmental conditions; b) inoculate these bacteria in sugarcane to evaluate their ability in plant growth-promotion. The study was carried in the Northeast of Brazil. Bacterial genera Burkholderia sp., Pantoea sp., Stenotrophomonas sp. and Enterobacter sp. were evaluated in different culture medium and later the bacterial isolates were inoculated in sugarcane evaluating the plant growth-promotion. Stenotrophomonas sp. and Pantoea sp. were tolerant to salinity and to different sources of carbon in acid medium and too tolerated high concentrations of pesticides and produced quorum sensing molecules (QS), but did not increase the dry matter production of sugarcane. Burkholderia sp. and Enterobacter sp. were more sensitive to salinity and pest control, but were more effective in plant growth-promotion. The tolerance of the bacteria to the adverse environmental conditions interfered negatively in the ability to plant growth-promotion.     

Effect of land use on the abundance and diversity of autotrophic bacteria as measured by ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO) large subunit gene abundance in soils

Elucidating the biodiversity of CO₂-assimilating bacterial communities under different land uses is critical for establishing an integrated view of the carbon sequestration in agricultural systems. We therefore determined the abundance and diversity of CO₂ assimilating bacteria using terminal restriction fragment length polymorphism and quantitative PCR of the cbbL gene (which encodes ribulose-1,5-biphosphate carboxylase/oxygenase). These analyses used agricultural soils collected from a long-term experiment (Pantang Agroecosystem) in subtropical China. Soils under three typical land uses, i.e., rice–rice (RR), upland crop (UC), and paddy rice–upland crop rotation (PU), were selected. The abundance of bacterial cbbL (0.04 to 1.25?×?10⁸ copies g^?1 soil) and 16S rDNA genes (0.05–3.00?×?10¹⁰ copies g^?1 soil) were determined in these soils. They generally followed the trend RR?>?PU?>?UC. The cbbL-containing bacterial communities were dominated by facultative autotrophic bacteria such as Mycobacterium sp., Rhodopseudomonas palustris, Bradyrhizobium japonicum, Ralstonia eutropha, and Alcaligenes eutrophus. Additionally, the cbbL-containing bacterial community composition in RR soil differed from that in upland crop and paddy rice–upland crop rotations soils. Soil organic matter was the most highly statistically significant factor which positively influenced the size of the cbbL-containing population. The RR management produced the greatest abundance and diversity of cbbL-containing bacteria. These results offer new insights into the importance of microbial autotrophic CO₂ fixation in soil C cycling.     

Bacterial inoculants for rice: effects on nutrient uptake and growth promotion

Beneficial soil bacteria are able to colonize plant root systems promoting plant growth and increasing crop yield and nutrient uptake through a variety of mechanisms. These bacteria can be an alternative to chemical fertilizers without productivity loss. The objectives of this study were to test bacterial inoculants for their ability to promote nutrient uptake and/or plant growth of rice plants subjected to different rates of chemical fertilizer, and to determine whether inoculants could be an alternative to nitrogen fertilizers. To test the interaction between putatively beneficial bacteria and rice plants, field experiments were conducted with two isolates: AC32 (Herbaspirillum sp.) and UR51 (Rhizobium sp.), and different nitrogen fertilization conditions (0%, 50%, and 100% of urea). Satisfactory results were obtained in relation to the nutrient uptake by plants inoculated with both isolates, principally when the recommended amount of nitrogen fertilizer was 50% reduced. These bacterial strains were unable to increase plant growth and grain yield when plants were subjected to the high level of fertilization. This study indicated that the tested inoculant formulations can provide essential nutrients to plants, especially when the levels of nitrogen fertilizers are reduced.     

Response of spring wheat (Triticum aestivum) to interactions between Pseudomonas species and Glomus clarum NT4

The effects of interactions between pseudomonads (Pseudomonas cepacia strains R55 and R85, P. aeruginosa strain R80, P. fluorescens strain R92, and P. putida strain R104) and the arbuscular mycorrhizal fungus Glomus clarum (Nicol. and Schenck) isolate NT4, on spring wheat (Triticum aestivum L. cv. Laura), grown under gnotobiotic and nonsterile conditions, were investigated. Although plant growth responses varied, positive responses to pseudomonad inoculants generally were obtained under gnotobiotic conditions. Shoot dry weight enhancement ranged from 16 to 48%, whereas root enhancement ranged from 82 to 137%. Shoot growth in nonsterile soil, however, was unaffected by pseudomonad inoculants, or reduced by as much as 24%. Shoot growth was unaffected or depressed by G. clarum NT4 whereas early root growth was enhanced by 38%. Significant interactions between the pseudomonad inoculants and G. clarum NT4 were detected. Typically, dual inoculation influenced the magnitude of response associated with any organism applied alone. The effect of these pseudomonads on G. clarum NT4 spore germination was investigated. Germination was inhibited when spores were incubated either on membranes placed directly on bacterial lawns of strains R85 and R104 (i.e., direct assay), or on agarose blocks separated from the bacteria by membranes (i.e., diffusion assay). When the agarose blocks were physically separated from the pseudomonad (i.e., volatile assay), there was no evidence of inhibition, suggesting that a nonvolatile, diffusible substance(s) produced by both strains R85 and R104 may inhibit G. clarum NT4 spore germination. Received: 11 December 1995     

Isolation and characterization of plant growth promoting endophytic bacterial isolates from root nodule of Lespedeza sp.

Thirty-nine endophytic bacterial strains were isolated from the nodule of Lespedeza sp. grown in two different locations of South Korea. All strains were checked for their plant growth promoting (PGP) abilities under in vitro conditions. Most of the isolates showed multiple PGP activity, i.e., indole acetic acid production, ACC deaminase activity, siderophore production, and phosphate solubilization. The strains were identified by using 16S rRNA gene sequence analysis as belonging to Alphaproteobacteria, Betaproteobacteria, Actinobacteria, and Firmicutes phylum with nine different genera Arthrobacter, Bacillus, Bradyrhizobium, Burkholderia, Dyella, Methylobacterium, Microbacterium, Rhizobium, and Staphylococcus. Gene nodA amplification showed positive results only for strains from Bradyrhizobium and Rhizobium genera. The strains from Bradyrhizobium and Rhizobium genera enhanced plant growth, nodulation, and acetylene reduction activity when inoculated on Vigna unguiculata L. (cowpea), whereas other strains did not induce nodule formation but enhanced plant growth. Herbaceous legume Lespedeza sp. formed root nodules with diverse bacterial group, and probably, these bacteria can be used for stimulating plant growth.     

The relationship of soil and leaf nutrients to rice leaf oranging

A symptom called leaf‐oranging, indicating a deficiency of many nutrients, occurs in paddy rice (Oryzasativa L.) when production expands into some upland soils. Rice (Gui Chou cv.) was grown in culture pots in a flooded, weathered, upland soil (Nacogdoches) and compared to rice growth in a flooded soil currently used for paddy rice production (Dacosta) in Texas to understand the soil and plant factors involved in leaf‐oranging. Fertilizer rates of 0, 10, and 100 mg N/kg as (NH₄)₂SO₄ were applied to each soil along with phosphorus (P) and potassium (K) fertilizer. The orange Leaf Index (OLI), a measure of leaf‐oranging, was determined weekly and increased to 60–70% for plants grown in the upland soil but its progression was delayed by higher N treatments. No leaf‐oranging was observed in the paddy soil. The soil evoking leaf‐oranging was low in silicon (Si) and high in iron (Fe). In addition, analysis of leaves from these plants showed 19–25% higher leaf ammonium‐nitrogen (NH₄‐N), 9–137% higher manganese (Mn) levels and lower total N:NH₄ concentration compared to normal rice leaves four weeks after transplanting. This inferred that leaf‐oranging probably was associated with some degree of NH₄‐N toxicity and antagonism with K. Leaf‐oranging was also associated with low calcium (Ca) assimilation or Ca uptake inhibition because of the heavy Fe‐oxide coating of the roots of the affected rice plants. In this experiment, leaf‐oranging was not associated with toxic levels of Fe or Mn.     

Accumulation of specific flavonoids in soybean (Glycine max (L.) Merr.) as a function of the early tripartite symbiosis with arbuscular mycorrhizal fungi and Bradyrhizobium japonicum (Kirchner) Jordan

This study is the first report assessing the effect of soil inoculation on the signalling interaction of Bradyrhizobium japonicum, arbuscular mycorrhizal fungi (AMF) and soybean plants throughout the early stages of colonisation that lead to the tripartite symbiosis. In a study using soil disturbance to produce contrasting indigenous AMF treatments, the flavonoids daidzein, genistein and coumestrol were identified as possible signals for regulating the establishment of the tripartite symbiosis. However, it was unclear whether soil disturbance induced changes in flavonoid root accumulation other than through changing the potential for AMF colonization. In this study, soil treatments comprising all possible combinations of AMF and B. japonicum were established to test whether (1) modifications in root flavonoid accumulation depend on the potential for AMF colonization, and (2) synthesis and accumulation of flavonoids in the roots change over time as a function of the early plant-microbial interactions that lead to the tripartite symbiosis. The study was comprised of two phases. First, maize was grown over 3-week periods to promote the development of the AM fungus Glomus clarum. Second, the interaction between soybean, G. clarum and B. japonicum was evaluated at 6, 10, 14 and 40 days after plant emergence. Root colonization by G. clarum had a positive effect on nodulation 14 days after emergence, producing, 30% more nodules which were 40% heavier than those on roots solely inoculated with B. japonicum. The tripartite symbiosis resulted in 23% more N₂ being fixed than did the simpler symbiosis between soybean and B. japonicum. The presence of both symbionts changed accumulation of flavonoids in roots. Daidzein and coumestrol increased with plant growth. However, development of the tripartite symbiosis caused a decrease in coumestrol; accumulation of daidzein, the most abundant flavonoid, was reduced in the presence of AMF.     

Interactions between mycorrhizal fungi and mycorrhizosphere bacteria during mineral weathering: Budget analysis and bacterial quantification

The impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition.     

Response of the soil bacterial community to the addition of toluene and toluene-degrading bacteria

Changes in soil bacterial communities after toluene and/or toluene degrading bacteria were added were monitored by growth on various media, and by the culture-independent method of Reverse Sample Genome Probing (RSGP). A total of 397 isolates that were cultured from toluene-amended and non-amended soil were identified using fatty acid methyl ester (FAME) analysis. In 75% of the soil samples, gram-positive bacteria dominated, primarily Bacillus sp. and Cellulomonas sp. In contrast, RSGP revealed Proteobacteria (α, β, and γ subgroups) to be the dominant species, with Bacillus sp. dominant in only one soil sample.In toluene-treated soil, FAME and RSGP analyses indicated that by day 5 the major bacterial populations were gram-negative bacteria, in particular, Pseudomonas sp., Acinetobacter sp., and Alcaligenes sp. When toluene and Pseudomonas putida D8 were coincidentally introduced, the proportion of Pseudomonas sp. in the bacterial population recovered using non-selective medium increased from 16 to 62% and then rapidly decreased to about 9%. When we used selective medium to monitor the population of P. putida D8, a rapid initial increase followed by a gradual decline was also observed. In samples analyzed by RSGP, D8 was one of the major species of the bacterial community at day 2, but its signal intensity dropped to 9.5% by day 5.The influence of D8 addition on the bacterial profile was monitored in growth-based examinations. Bacillus sp. and Pseudomonas sp. were initially dominant. By day 5, Bacillus sp. decreased while the Proteobacteria, (including Acinetobacter sp., Agrobacterium sp., Alcaligenes sp., Burkholderia sp., Erwinia sp., and Pseudomonas sp.) increased. At the same time, D8 decreased to a level indistinguishable from background. Conversely, RSGP analysis revealed the population dominance of P. putida (including D8) and Rhizobium fredii at day 2. Populations shifted toward Agrobacterium tumefaciens, Bacillus subtilis, R. fredii, and D8 by day 5.P. putida D8 levels could be monitored using RSGP when cultivation failed. However, cultivation of Bacillus sp. was always successful, while the organism was only occasionally detected by RSGP. While cultivation and RSGP methods comparably detected the same major bacterial populations, the overall bacterial diversity was greater with RSGP than with growth-based testing.     

Physiological enhancement of early growth of rice seedlings (Oryza sativa L.) by production of phytohormone of N2-fixing methylotrophic isolates

Three plant-growth promoting, N₂-fixing methylotrophic strains isolated from rice cultivars (Oryza sativa L.), viz, Methylobacterium sp. CBMB20, Enterobacter sp. CBMB30, Burkholderia sp. CBMB40, were selected, and their activities in promoting the early growth of rice were studied. Seeds treated with the methylotrophic strains improved seed germination, seedling vigor index (SVI), and biomass of rice seedlings. The methylotrophic population in the treated seedlings increased in the vegetative stages when compared to seeding stages. Treated seedlings showed a higher accumulation of plant hormones viz trans-zeatin riboside, isopentenyladenosine, and indole-3-acetic acid than untreated seedlings. Plant hormones were detected immunologically using the phytodetek kit. Conformational evidence suggested that cytokinins were produced by the epiphytic bacteria colonizing the plants rather than by the plants themselves. In addition, the inoculated early stage rice seedlings also exhibited a wide range of acetylene reduction activity. The results suggest the potential use of these bacteria to stimulate germination, SVI, and biomass production, which is mediated by production of plant hormone accumulation and nitrogen fixation.     

Microflora of extreme arid Atacama Desert soils

Surface and subsurface soil samples from the most arid region within the Atacama Desert, Chile, were analyzed for total organic carbon (TOC), phospholipid fatty acids (PLFA) and culturable bacteria. TOC content was determined to range between 560 and 765 μg/g. PLFA analysis indicated 2.0×10⁶-1.0×10⁷ cell equivalents/g. Culturing of soil extracts on R2A and TSA media yielded 1.6×10³-4.6×10³ CFU/g, and 200-300 CFU/g heat shock survivors. Twenty isolated strains were identified based on analysis of 16S rRNA gene sequences, and divided into eight phylogenetic groups, including Rhodopseudomonas, Sphingomonas sp., Mesorhizobium sp., Asticcacaulis sp., Bradyrhizobium sp., Bacillus subtilis, Bacillus pumilus, and Burkholderia sp.