Azospirillum Brasilense Strain Research Articles

The response of wheat genotypes to inoculation with Azospirillum brasilense in the field

The response of wheat (Triticum aestivum) genotypes to inoculation with different growth promoting bacterial inoculants is unclear. Five wheat genotypes that showed a differential response to inoculation with three Azospirillum brasilense strains under controlled conditions were sown in field experiments with and without inoculation in two environments in 2010 and 2011 in north-western New South Wales. Inoculum was applied in furrow to whole plots within a split plot design. Plant height, root architecture, above ground dry matter accumulation, relative chlorophyll, Normalized Difference Vegetation Index (NDVI), grain yield, biomass at maturity, tiller number and thousand kernel weight (TKW) were assessed. Inoculation improved some traits, particularly in the early growth phase; however these effects diminished with time. Little effect of bacterial inoculum on grain yield was observed with the exception of one genotype that produced significantly higher yield in the presence of inoculum. While genotype×inoculation interactions were significant for some traits including TKW, no interaction was observed for biomass and grain yield. The bacterial inoculum did persist in rhizospheric soil with time. However, persistence estimated throughout the season using the most probable number technique and terminal restriction fragment length polymorphism (T-RFLP), was observed to be higher early in the season in inoculated plots and reduced with time.

Construction of probe of the plant growth-promoting bacteria Bacillus subtilis useful for fluorescence in situ hybridization

Strains of Bacillus subtilis are plant growth-promoting bacteria (PGPB) of many crops and are used as inoculants. PGPB colonization is an important trait for success of a PGPB on plants. A specific probe, based on the 16s rRNA of Bacillus subtilis, was designed and evaluated to distinguishing, by fluorescence in situ hybridization (FISH), between this species and the closely related Bacillus amyloliquefaciens. The selected target for the probe was between nucleotides 465 and 483 of the gene, where three different nucleotides can be identified. The designed probe successfully hybridized with several strains of Bacillus subtilis, but failed to hybridize not only with B. amyloliquefaciens, but also with other strains such as Bacillus altitudinis, Bacillus cereus, Bacillus gibsonii, Bacillus megaterium, Bacillus pumilus; and with the external phylogenetic strains Azospirillum brasilense Cd, Micrococcus sp. and Paenibacillus sp. The results showed the specificity of this molecular probe for B. subtilis.

Inoculation of Brachiaria spp. with the plant growth-promoting bacterium Azospirillum brasilense: An environment-friendly component in the reclamation of degraded pastures in the tropics

Estimates are that in Brazil there are about 180 million hectares of pasturelands, 70% with some degree of degradation. Reclamation of such areas demands re-establishment of soil fertility, plant growth and forage production, and microbial inoculants might help in these processes. We evaluated the ability of two strains of Azospirillum brasilense to promote the growth of two genotypes of Brachiaria spp. (=Urochloa spp.). The experiments were set up at three different sites in Brazil, and forage production estimated for 26 cuts in two years. On average, increases of 5.4% and 22.1% in response to N-fertilizer alone and to N-fertilizer in combination with Azospirillum, respectively, were observed over the non-inoculated and non-N-fertilized control treatment. Increase in N accumulation in the biomass in response to Azospirillum was equivalent to a second application of 40kg of N-fertilizer ha−1. Estimates attributed to the inoculation were of gains of 0.103MgCha−1, corresponding to 0.309Mg CO2-eq ha−1. Inoculation with Azospirillum may represent a key component of programs to reclaim degraded pastures and help sequestration of CO2 from the atmosphere.

A need for disclosure of the identity of microorganisms, constituents, and application methods when reporting tests with microbe-based or pesticide-based products

Plant growth-promoting microorganisms, biological control agents, pesticides, and a variety of stimulants to enhance plant performance are commonly tested and commercially applied worldwide on increasing scales each year (Bashan et al. 2014; Calvo et al. 2014; Lugtenberg and Kamilova 2009). In recent years, inoculation of plants with microorganisms to enhance productivity has become widespread, with more sophisticated and complex formulations and application methods. These formulations use a variety of application techniques, such as using natural and synthetic polymers or add more than one microorganism to the inoculants. These microbial consortia in inoculants may have over ten different microorganisms. Inoculants may have synthetic vitamins, plant hormones, and humic and fulvic acids. Other inoculants add different plant or algae or seaweed extracts, protein hydrolytes and amino acids as stimulants, as well as bulking materials, such as clays, minerals (vermiculite and perlite), talcum, or undisclosed soil fractions. Numerous adhesives, surfactants, stabilizing and dispersing materials, and preservatives to enhance survival and dispersal of the microorganisms are commonly added. The identity of these components in microbial formulations is often not disclosed in the product label. Specific details of application are usually explained by the manufacturer on the container label, but rarely in a formal publication. As product formulations change, performance of bacterial strains in the product may change. Hence, it might not be possible to objectively compare the effects of an inoculated microorganism in laboratory experiments with the effects of the same microbe in a commercial formulation. This results from some components in the formulations having synergistic bioactivities that are greater than a single strain of microorganism. As an example, the plant growth-promoting bacterium Azospirillum brasilense strain AZ39 is one of the most common Azospirillum strains used in Latin America. Yet, its performance significantly varies, depending on the specific formulation and the method of inoculation. Similar phenomenon occurs with rhizobia. Pesticides are commonly used in agriculture and are classified, according to the pest organism, in insecticides, fungicides, herbicides (weeds killers), nematocides, and rodenticides. The first three pesticides are those most used. Pesticides differ greatly for their chemical structures, and this result in a great variety of toxicological properties, most of them contain aromatic rings and some are chlorinated, just to mention a few chemical characteristics. Field rates depend on several factors including soil type (Bremner and Mulvaney 1976; Cervelli et al. 1976). Usually, pesticides are applied in formulations containing several other constituents often not disclosed in the product label, as mentioned above for the microbial inocula. These additives may include solvents, by-products of the target compounds, salts, chemical vehicles of the target compound, etc. Obviously toxicological studies of the target pesticide should also consider the effect of all other constituents; these effects may be synergic or antagonist with those by the target pesticide (Cervelli et al. 1976). * Yoav Bashan ybb0001@auburn.edu

Promotion of Peanut Growth by Co-inoculation with Selected Strains of Bradyrhizobium and Azospirillum

The ability of inoculated rhizobial strains to increase root nodulation of host legumes often depends on their competitiveness with existing native soil strains. Results of studies to date on rhizobial inoculation for improvement of peanut (Arachis hypogaea L.) production in Argentina have been inconsistent and controversial. In many cases, nodulation and yield of peanut crops have been increased by inoculation of specific rhizobial strains. Native peanut-nodulating strains are generally present in soils of agricultural areas, but their growth-promoting effect is often lower than that of inoculated strains. Many species of the genus Bradyrhizobium interact in a host-specific manner with legume species and form nitrogen-fixing root nodules. Other free-living rhizobacteria such as species of the genus Azospirillum are facultatively capable of interacting with legume roots and promoting plant growth. We evaluated and compared the effects of various single inoculation and co-inoculation treatments on peanut growth parameters in greenhouse and field experiments. In the greenhouse studies, co-inoculation with various Bradyrhizobium strains (native 15A and PC34, and recommended peanut inoculant C145), and Azospirillum brasilense strain Az39 generally resulted in increases in the measured parameters. The growth-promoting effect of 15A was similar to or higher than that of C145. In the field studies, 15A-Az39 co-inoculation had a greater promoting effect on measured growth parameters than did C145-Az39 co-inoculation. Our findings indicate that careful selection of native rhizobacterial strains adapted to peanut soils is useful in strategies for growth promotion, and that 15A in particular is a promising candidate for future inoculant formulation.

Вплив Azospirillum brasilense 10/1на асоціативну азотфіксацію і внутрішньосортовий поліморфізм тритикале ярого

It is shown, that the perspective Ukrainian sorts of spring triticale characterizes by considerable polymorphism by associative N2-fixing ability in root zone of plants. Application of active strain Azospirillum brasilense 10/1 promotes the decline of variability of this sign within the limits of sort, increase potential nitrogen activity is on the average in 3,2-4,7 times and also distributing normalizations in the selections of the inoculated plants.

Effect of azospirillum lectins on the activity of proteolytic enzymes and their inhibitors in wheat seedling roots

The lectins of associative nitrogen-fixing strains Azospirillum brasilense Sp7 and Sp245 were shown to exerte a multidirectional effect on the activity of acidic (pH 3.5), neutral (6.8), and alkaline (pH 7.8) proteinases. The lectin of the epiphytic A. brasilense Sp7 decreased proteolytic activity at all pH values, whereas the lectin of the endophytic A. brasilense Sp245 activated neutral and alkaline proteinases, while not affecting the alkaline ones. Experiments with protease inhibitors made it possible to conclude that the lectins of the studied A. brasilense strains alter the ratio between the activities of different protease types in germinating seeds. The activity of trypsin inhibitors in wheat seedling roots was found to increase in the presence of the lectins. Our results indicate a broader spectrum of effects of azospirilla lectins on the host plant organism.

Biofertilization with Azospirillum brasilense improves in vitro culture of Handroanthus ochraceus, a forestry, ornamental and medicinal plant

Biofertilization with plant growth-promoting rhizobacteria is a potential alternative to plant productivity. Here, in vitro propagation of Handroanthus ochraceus (yellow lapacho), a forest crop with high economic and environmental value, was developed using the Azospirillum brasilense strains Cd and Az39 during rhizogenesis. Epicotiles of in vitro plantlets were multiplied in Woody Plant Medium (WPM). For rooting, elongated shoots were transferred to auxin-free Murashige-Skoog medium with Gamborg's vitamins and WPM, both at half salt concentration (½MSG and ½WPM), and inoculated with Cd or Az39 at the base of each shoot. Anatomical studies were performed using leaves cleared and stained with safranin for optical microscopy and leaves and roots metalized with gold-palladium for scanning electron microscopy (SEM). In ½WPM auxin-free medium, A. brasilense Cd inoculation produced 55% of rooting, increased root fresh and dry weight (45% and 77%, respectively), and led to lower stomata size and density with similar proportion of open and closed stomata. Both strains selectively increased the size or density of glandular trichomes in ½MSG. Moreover, bacteria were detected on the root surface by SEM. In conclusion, the difference in H. ochraceus response to A. brasilense inoculation depends on the strain and the plant culture media. Cd strain enhanced rooting in auxin-free ½WPM and produced plantlets with features similar to those expected in ex vitro plants. This work presents an innovative in vitro approach using beneficial plant-microorganism interaction as an ecologically compatible strategy in plant biotechnology.

THE RESURRECTION PLANT TRIPOGON SPICATUS (POACEAE) HARBORS A DIVERSITY OF PLANT GROWTH PROMOTING BACTERIA IN NORTHEASTERN BRAZILIAN CAATINGA

Plant species that naturally occur in the Brazilian Caatinga(xeric shrubland) adapt in several ways to these harsh conditions, and that can be exploited to increase crop production. Among the strategic adaptations to confront low water availability, desiccation tolerance stands out. Up to now, the association of those species with beneficial soil microorganisms is not well understood. The aim of this study was to characterize Tripogon spicatusdiazotrophic bacterial isolates from the Caatingabiome and evaluate their ability to promote plant growth in rice. Sixteen bacterial isolates were studied in regard to their taxonomic position by partial sequencing of the 16S rRNA gene, putative diazotrophic capacity, in vitro indole-acetic acid (IAA) production and calcium phosphate solubilization, metabolism of nine different C sources in semi-solid media, tolerance to different concentrations of NaCl to pHs and intrinsic resistance to nine antibiotics. Finally, the ability of the bacterial isolates to promote plant growth was evaluated using rice (Oryza sativa) as a model plant. Among the 16 isolates evaluated, eight of them were classified as Enterobacteriaceae members, related to Enterobacter andPantoeagenera. Six other bacteria were related toBacillus, and the remaining two were related toRhizobiumand Stenotrophomonas.The evaluation of total N incorporation into the semi-solid medium indicated that all the bacteria studied have putative diazotrophic capacity. Two bacteria were able to produce more IAA than that observed for the strain BR 11175Tof Herbaspirillum seropedicae.Bacterial isolates were also able to form a microaerophilic pellicle in a semi-solid medium supplemented with different NaCl concentrations up to 1.27 mol L-1. Intrinsic resistance to antibiotics and the metabolism of different C sources indicated a great variation in physiological profile. Seven isolates were able to promote rice growth, and two bacteria were more efficient than the reference strainAzospirillum brasilense, Ab-V5. The results indicate the potential of T. spicatus as native plant source of plant growth promoting bacteria.

Azospirillum brasilense Enhances Recycling of Fish Effluent to Support Growth of Tomato Seedlings

Increasing environmental concerns and growing demand for safer and sustainable food production presents significant challenges for agricultural production. One potential technique, which could help improve crop productivity without adverse impact on the environment, is the use of beneficial microbes in crop production systems. This study evaluated the effects of three Azospirillum brasilense strains on tomato seedlings fertilized with effluent from freshwater fish aquaculture. Seeds were inoculated with A. brasilense strains Sp7, Sp7-S and Sp245 before sowing and after transplanting. Seedlings were raised under controlled greenhouse conditions with natural light. Inoculated seedlings produced longer roots (67%), bigger leaves (22%), higher seedling biomass (>33%), and greater protein (15%) and endogenous plant IAA (94%) contents. Inoculation with Sp7 and Sp245 increased the number of leaves and stem diameter by 8 and 10%, respectively. Seedling height was also increased by inoculation, but only with Sp7. In addition, seedlings inoculated with strains Sp7-S and Sp245 had higher total phosphorus content, while inoculation with Sp245 increased the activity of the enzyme peroxidase, which suggests that plant defense responses had been triggered. The result demonstrates the potential of the applied A. brasilense strains to enhance the usefulness of fish effluent as fertilizer for tomato seedling production.

Microscopic and proteomic analysis of Zea mays roots (P30F53 variety) inoculated with Azospirillum brasilense strain FP2

Plant growth-promoting rhizobacteria (PGPR) are considered to have a beneficial effect on host plants. Azospirillum brasilense is a diazotroph associated with important agricultural crops such as maize and wheat, and has been used as model organism to investigate associative plant growth promotion. In this study, we have employed scanning electronic microscopic to observe the presence of bacterium on the root surface. Two-dimensional gel electrophoresis and mass spectrometry were used to analyze the changes in protein profile of maize roots in response to A. brasilense strain FP2 7 days after inoculation and we observed 46 differently expressed protein spots. We report the identification of three of these proteins.

Improved potato microclonal reproduction with the plant growth-promoting rhizobacteria Azospirillum

Microclonal propagation in vitro is being actively used in the production of healthy planting material of food and ornamental plants. However, it needs further improvement to increase the growth rates of microclones in vitro and enhance regenerant survivability ex vitro. A promising approach to this end could be inoculating in vitro-micropropagated plants with plant growth-promoting rhizobacteria, specifically Azospirillum. However, the influence of Azospirillum inoculation on microclone behavior throughout the production process, including plant adaptation ex vitro and food crop productivity, has been underinvestigated. In this study, in vitro-growing potato (Solanum tuberosum L.) microclones were inoculated with Azospirillum brasilense strain Sp245. The microclones were then grown on in soil in the greenhouse and field, with the experiment lasting for 120 days. Root-associated bacteria were identified immunochemically, and the mitotic index of root meristematic cells was determined by a cytological method. The plant morphological parameters determined were shoot length, number of nodes per shoot, number of roots per plant, maximal root length, leaf area, percentage of surviving plants in the soil, and tuber yield and weight. Our results show that bacterial inoculation of potato microclones in vitro enhances plant adaptive capacity ex vitro and increases minituber yield. The percent survival index of field-grown inoculated plants was 1.5-fold greater than that of uninoculated plants. The overall tuber weight per plant was more than 30 % greater in the inoculated plants than it was in the control ones. For all cultivars on average, tuber yield per square meter increased by more than 45 % as a result of inoculation in vitro. This study is the first to report that Azospirillum inoculation of potato microclones not only improves the quality of planting material produced in vitro but also significantly increases minituber yield through enhancing plant adaptive capacity in the field.

Composition and activity of endophytic bacterial communities in field-grown maize plants inoculated with Azospirillum brasilense

The application of agricultural practices in which non-leguminous plants are inoculated with growth-promoting diazotrophic bacteria is gaining importance worldwide. Nevertheless, an efficient strategy for using this inoculation technology is still lacking, and a better comprehension of the environmental factors that influence a plant’s ability to support its associative bacterial community is indispensable to achieving standardized inoculation responses. To address the effects of nitrogen (N)-fertilization on the diversity of both the total and metabolically active endophytic bacterial communities of field-grown maize plants, we extracted total DNA and RNA from maize plants inoculated with Azospirillum brasilense strain Ab-V5 that were growing in Oxisol and treated with regular and low levels of N-fertilizers (RN and LN, respectively). Four clonal libraries were constructed and sequenced and the dominant populations analyzed. Partial description of the bacterial diversity indicated that plants receiving RN- and LN-treatments can maintain bacterial communities with similar diversity indexes for the total endophytic bacterial community, although the communities of Novosphingobium and Methylobacterium were unevenly distributed. Fertilization management had a stronger effect on the dominant populations of the metabolically active bacterial community, and 16S rRNA gene libraries from RN plants suggested a lower diversity of such populations in comparison with libraries from LN plants. The agronomic parameters obtained at the end of the crop season indicated that the inoculation treatment was efficient in promoting plant growth. However, the combination of regular treatments with N-fertilizers and plant inoculation did not have an additive effect and actually tended to decrease crop productivity.

Accumulation of intra-cellular polyphosphate in Chlorella vulgaris cells is related to indole-3-acetic acid produced by Azospirillum brasilense

Accumulation of intra-cellular phosphate, as polyphosphate, was measured when the microalga Chlorella vulgaris was immobilized in alginate with either of two wild-type strains of the microalgae growth-promoting bacterium Azospirillum brasilense or their corresponding IAA-attenuated mutants. Wild type strains of A. brasilense induced higher amounts of intra-cellular phosphate in Chlorella than their respective mutants. Calculations comparing intra-cellular phosphate accumulation by culture or net accumulation by the cell and the amount of IAA that was produced by each of these strains revealed that higher IAA was linked to higher accumulations of intra-cellular phosphate. Application of four levels of exogenous IAA reported for A. brasilense and their IAA-attenuated mutants to cultures of C. vulgaris enhanced accumulation of intra-cellular phosphate; the higher the content of IAA per culture or per single cell, the higher was the amount of accumulated phosphate. When an IAA-attenuated mutant was complemented with exogenous IAA, accumulation of intra-cellular phosphate at the culture level was even higher than phosphate accumulation with the respective wild type strains. When calculating the net accumulation of intra-cellular phosphate in the complementation experiment, net intra-cellular phosphate induced by the IAA-attenuated mutant was completely restored and was similar to the wild strains. We propose that IAA produced by A. brasilense is linked to polyphosphate accumulation in C. vulgaris.

Robust biological nitrogen fixation in a model grass-bacterial association.

Nitrogen-fixing rhizobacteria can promote plant growth; however, it is controversial whether biological nitrogen fixation (BNF) from associative interaction contributes to growth promotion. The roots of Setaria viridis, a model C4 grass, were effectively colonized by bacterial inoculants resulting in a significant enhancement of growth. Nitrogen-13 tracer studies provided direct evidence for tracer uptake by the host plant and incorporation into protein. Indeed, plants showed robust growth under nitrogen-limiting conditions when inoculated with an ammonium-excreting strain of Azospirillum brasilense. (11)C-labeling experiments showed that patterns in central carbon metabolism and resource allocation exhibited by nitrogen-starved plants were largely reversed by bacterial inoculation, such that they resembled plants grown under nitrogen-sufficient conditions. Adoption of S. viridis as a model should promote research into the mechanisms of associative nitrogen fixation with the ultimate goal of greater adoption of BNF for sustainable crop production.

Maximizing Fish Effluent Utilization for Vegetable Seedling Production by Azospirillum Brasilense

Recycling of nutrients from organic sources and modifying farming practices towards sustainable agriculture have gained considerable attention in recent years. This is due to the growing awareness of the declining environmental quality and arable land, and significant depletion of oil and water reserves that drive agriculture production. This study evaluated the impacts of three Azospirillum brasilense strains (i.e. Sp7, Sp7-S and Sp245) on the growth of vegetable seedlings (i.e. tomato, lettuce and cucumber) fertilized with fish effluent. Seeds and seedlings were inoculated prior to germination and transplanting, respectively, and were grown in a greenhouse with natural light. Results show that inoculation with these strains increased root length and endogenous plant IAA (indole-3-acetic acid) of all vegetables. Inoculated tomato seedlings produced bigger leaves, higher dry plant biomass and protein content. Likewise, taller plants with bigger stems and more leaves, and higher fresh plant biomass were documented, but with Sp7 only. Strain Sp245 also triggered an increase of peroxidase enzyme activity. In lettuce, inoculation produced taller seedlings, more leaves and higher peroxidase activity. Chlorophyll and protein content were also increased, but with Sp7 only. In cucumber, inoculated seedlings increased seedling root biomass with higher total phosphorus content and peroxidase activity. Furthermore, inoculation caused little or no adverse impact on the fish effluent bacterial community indicating that these strains can be integrated into production system that utilizes fish effluent as a fertilizer, e.g. Aquaponics. A. brasilense could be a valuable agent to help maximize the usefulness of fish effluent or wastewater from freshwater aquaculture for plant production.

Involvement of indole-3-acetic acid produced by Azospirillum brasilense in accumulating intracellular ammonium in Chlorella vulgaris

Accumulation of intracellular ammonium and activities of the enzymes glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were measured when the microalgae Chlorella vulgaris was immobilized in alginate with either of two wild type strains of Azospirillum brasilense or their corresponding indole-3-acetic acid (IAA)-attenuated mutants. After 48 h of immobilization, both wild types induced higher levels of intracellular ammonium in the microalgae than their respective mutants; the more IAA produced, the higher the intracellular ammonium accumulated. Accumulation of intracellular ammonium in the cells of C. vulgaris followed application of four levels of exogenous IAA reported for A. brasilense and its IAA-attenuated mutants, which had a similar pattern for the first 24 h. This effect was transient and disappeared after 48 h of incubation. Immobilization of C. vulgaris with any bacteria strain induced higher GS activity. The bacterial strains also had GS activity, comparable to the activity detected in C. vulgaris, but weaker than when immobilized with the bacteria. When net activity was calculated, the wild type always induced higher GS activity than IAA-attenuated mutants. GDH activity in most microalgae/bacteria interactions resembled GS activity. When complementing IAA-attenuated mutants with exogenous IAA, GS activity in co-immobilized cultures matched those of the wild type A. brasilense immobilized with the microalga. Similarity occurred when the net GS activity was measured, and was higher with greater quantities of exogenous IAA. It is proposed that IAA produced by A. brasilense is involved in ammonium uptake and later assimilation by C. vulgaris.

Phosphorus fertilization associated to inoculation of maize with diazotrophic bacteria

The effects of diazotrophic bacteria inoculation associated to phosphate fertilization on plant growth and leaf gas exchange parameters in maize plants (Zea mays L.) were investigated in the present study. Maize plants were grown in 13-L pots filled with clayey Rhodic Hapludox in a greenhouse. Treatments were arranged in a randomized block design in a 4 × 2 factorial: four seed inoculation treatments [control (non-inoculated); inoculation with Azospirillum brasilense strain AbV5; inoculation with Herbaspirillum seropedicae strain SmR1; and inoculation with two bacteria strains (A. brasiliense + H. seropedicae)] and two phosphate fertilization levels [no fertilized or fertilized with phosphorus (300 mg dm–3 of P2O5)]. Phosphorus fertilization resulted in higher plant height, stem diameter, number of leaves per plant, leaf area, dry matter yield of leaves, stems and sheaths of maize plants, regardless of seed inoculation with diazotrophic bacteria. Seed inoculation with A. brasilense and H. seropedicae increased in 42% of the volume root, in 52% of the root dry matter and 25% of the plant height of maize, indicating an increase in the phosphorus solubilization or higher phosphorus use provided by the maize root system. Seed inoculation with A. brasilense associated to phosphorus fertilization increased in 23% of the relative chlorophyll content, resulting in higher metabolic structure to the photosynthetic activity of maize plants. The leaf CO2 assimilation rate was not affected by the phosphorus fertilization and maize seed inoculation with A. brasilense and H. seropedicae. Key words: Plant growth promoting bacteria, phosphate solubilization, gas exchange, Azospirillum brasilense, Herbaspirillum seropedicae, Zea mays.

Response of lettuce seedlings fertilized with fish effluent to Azospirillum brasilense inoculation

The continuous use of agrochemical inputs in modern agriculture for better crop productivity has resulted in unexpected environmental impact. This issue has raised public interest in exploring environmental friendly sustainable practices. In this study, three strains of Azospirillum brasilense (Sp7, Sp7-S and Sp245) were evaluated for their impacts on the growth of lettuce seedlings grown with fish effluent (FE) as a source of nutrients. Lettuce seeds were inoculated with these strains before sowing and at transplanting, and grown under greenhouse condition with natural light. Despite the existing indigenous microflora and low level of nutrients in the FE, the A. brasilense strains survived at populations ranging from 5 to 6 cfu g− 1 of roots and altered important agronomic traits, which led to growth enhancement. In particular, inoculated seedlings showed significant increase in the number of leaves, seedling height and root length. Chlorophyll and protein content were also improved, but only with Sp7 strain. However, the expression of pathogenesis-related protein, i.e., peroxidase, and level of endogenous indole-3-acetic acid increased by more than 50% in response to inoculation with the strains. Azospirillum inoculation also showed little or no adverse impact on the FE bacterial community indicating that it can be incorporated into a system that uses FE as a nutrient source, e.g., aquaponics. Thus, A. brasilense could be a valuable agent to help maximize the usefulness of FE or wastewater from freshwater aquaculture to further support plant growth.

Synthesis and bactericidal activity of substituted cyclic acetals

A series of substituted cyclic acetals were synthesized and tested for their bactericidal activity against bacteria strain Azospirillum brasilense Sp245.