Azospirillum Strains Research Articles

Raman spectroscopic and TEM monitoring of selenite and selenate reduction by the bacterium Azospirillum thiophilum with the formation of selenium(0) nanoparticles: Effects of sulfate

Microbial reduction of selenium oxyanions, highly soluble, mobile and toxic inorganic selenium compounds, to insoluble selenium nanoparticles (Se NPs) is a widely spread phenomenon which is of geochemical, environmental and biotechnological importance. While selenite bioreduction is known for a wide variety of microorganisms, selenate bioreduction is not so common and has mostly been documented for anaerobes, with merely a few reported cases related to aerobic or microaerobic conditions. In some biogenic Se NPs of microbial origin, the presence of sulfur was detected together with selenium in Se NPs, particularly when increased concentrations of sulfate were present in the medium. In this work, the bacterial strain Azospirillum thiophilum BV-S, isolated earlier from a sulfur-containing aqueous environment (Lavrinenko et al. (2010), https://doi.org/10.1099/ijs.0.018853-0), has been shown to reduce selenite to Se NPs also in the presence of 7 mM sulfate in aerobic conditions. Raman spectroscopy was used to monitor the crystallinity and composition of Se NPs formed within the bacterial biomass in the presence of selenite and in the resulting isolated Se NPs, and their spherical morphology was visualised using transmission electron microscopy (TEM). While Se NPs both within the biomass and after isolation gave a typical strong broadened band at 248 cm−1 related to the stretching Se–Se vibrations in amorphous Se0, Raman spectrum of the biomass grown with 1 mM selenite + 7 mM sulfate showed also a weaker band at 348 cm−1 typical of the stretching Se–S mode. The absence of the latter band in Raman spectra of the isolated Se NPs indicates that the Raman-detected Se–S bonds most probably occur in intermediate substances such as selenodiglutathione (GS–Se–SG), an intermediary product in the Painter-type reaction of selenite reduction, which is known to undergo further enzymatic transformations in bacteria resulting in the formation of Se0.Strain A. thiophilum BV-S has also been found, for the first time for bacteria of the genus Azospirillum, to be capable of reducing selenate (SeVIO42–) under static conditions (similar to microaerobic conditions common to habitats of many Azospirillum species in different environments), but not in aerobic conditions, with the formation of Se NPs. The latter, giving a reddish coloration to the bacterial biomass, were characterised by TEM as round-shaped electron-dense structures over bacterial cell images. Raman spectra of the bacterial biomass after cultivation with 5 mM selenate (with or without added sulfate) showed a similar single band at ca. 248 cm−1 in amorphous Se NPs, although 5 mM sulfate slowed down their formation. However, no signs of sulfur covalently bound to Se were observed in Raman spectra in this case. These results indicate a possible negligible role of the selenodisulfide-involving pathway in selenate reduction by A. thiophilum with a noticeable possible interference of sulfate in the process of selenate uptake (i.e., a common transport route) by A. thiophilum cells.

The diazotrophic bacteria Azospirillum baldaniorum and A. brasilense improve wheat seedlings' nitrogen budget through ammonia scavenging

Besides N2 fixation, we consider that other diazotrophic traits can be explored to increase plants' nitrogen (N) budget. Here, we report initial results of the capacity of the diazotrophic plant growth promoting rhizobacteria Azospirillum baldaniorum and A. brasilense to improve wheat seedlings' N budget through ammonia (NH3) scavenging. We inoculated wheat seedlings with two Azospirillum strains (A. baldaniorum Sp245 and A. brasilense ARG2) and determined its effect on plant biomass, N content and N isotopic signatures (i.e., δ15N). Furthermore, using bipartite Petri dishes, we grew the Azospirillum strains under increasingly alkaline conditions (from pH 7.5 to 10.0), which created a gradient of atmospheric NH3 concentrations ([NH3]), and we used Saccharomyces cerevisiae mutants to explore the involvement of the AMT/MEP/Rh proteins in atmospheric NH3 scavenging. Wheat seedlings inoculated with A. baldaniorum Sp245 and A. brasilense ARG2 increased their N content by 65 and 94 % (respectively), and their negative N isotopic signatures (around −10 ‰, which contrasted with positive signatures in control plants) were compatible with NH3 transport through AMT/MEP/Rh transporters, but not with N2 fixation. Furthermore, increasing the atmospheric [NH3] stimulated the growth rate of the Azospirillum strains up to 5-fold in relation to ambient atmospheric [NH3], showing that both Azospirillum strains scavenged the atmospheric NH3 and used it to grow. Our data clearly show that: i) NH3 scavenging by A. baldaniorum Sp245 and A. brasilense ARG2 is involved in increasing plant's N budget; and ii) NH3 transport through AMT/MEP/Rh protein family transporters is involved in microbial NH3 scavenging. This overlooked microbial trait can be an interesting tool to mitigate atmospheric [NH3], especially in farming environments.

Secondary products and molecular mechanism of calcium oxalate degradation by the strain Azospirillum sp. OX-1

The oxalate-carbonate pathway (OCP) involves degradation of soil oxalate to carbonate. To exploit and manage this natural mineralization of assimilated atmospheric CO2 into stable carbonates, improved understanding of this complex biotransformation process is needed. A strain of oxalate-degrading bacteria, Azospirillum sp. OX-1, was isolated from soil, and its secondary products of calcium oxalate degradation were analyzed and characterized using SEM, XRD, TG/DTG-DTA and FTIR-spectroscopy. The molecular mechanism of calcium oxalate degradation was also analyzed using proteomics. The results showed, for the first time, that OX-1 could not only degrade calcium oxalate to calcium carbonate, but also that the process was accompanied by synthesis of methane. Proteomic analysis demonstrated that OX-1 has a dual enzyme system for calcium oxalate degradation, using formyl-CoA transferase (FRC) and thiamine pyrophosphate (ThDP)-dependent oxalyl-CoA decarboxylase (OXC) to form calcium carbonate. Up-regulated expression of enzymes related to methane synthesis was also detected during calcium oxalate degradation. Since methane is also a potent greenhouse gas, these new results suggest that the utility of exploiting the OCP to reduce atmospheric CO2 must be re-evaluated and that further studies should be conducted to reveal how widespread the methane producing capacity of strain OX-1 is in other bacteria and soil environments.

Tracking maize colonization and growth promotion by Azospirillum reveals strain-specific behavior and the influence of inoculation method

Inoculation of Azospirillum in maize has become a standard practice in Latin America. However, information on the behavior and population survival of the Azospirillum post-inoculation is scarce, making standardization difficult and generating variations in inoculation efficiency across assays. In this study, we tracked the colonization of three agriculturally relevant Azospirillum strains (Ab-V5, Az39, and the ammonium excreting HM053) after different inoculation methods in maize crops by qPCR. Besides, we assessed their ability to promote maize growth by measuring biometric parameters after conducting a greenhouse essay over 42 days. Inoculated plants exhibited Azospirillum population ranging from 103 to 107 cells plant−1 throughout the experiment. While all strains efficiently colonized roots, only A. argentinense Az39 demonstrated bidirectional translocation between roots and shoots, which characterizes a systemic behavior. Optimal inoculation methods for plant growth promotion varied among strains: soil inoculation promoted the best maize growth for the Ab-V5 and Az39 strains, while seed inoculation proved most effective for HM053. The findings of this study demonstrate that the inoculation method affects the behavior of Azospirillum strains and their effectiveness in promoting maize growth, thereby guiding practices to enhance crop yield.

Isolation of Azospirillum spp and Evaluation of its Plant Growth Promoting Abilities

Background: This study aimed to isolate Azospirillum species from the soil environment and assess their plant growth-promoting abilities. Soil samples were collected from 10 different agricultural sites. The bacteria were isolated by serially diluting the soil samples and each aliquot was transferred into a Nitrogen-free bromothymol blue medium and then incubated for 7 days at 37°C. The isolates were further screened based on their morphological, biochemical and plant growth phytohormone production. The Fourier Transform Infrared Spectrophotometer will be used to elucidate the functional groups present in the isolates. Furthermore, the isolates were subjected to molecular identification. The results showed that Seventeen (17) bacteria were isolated from the soil samples of different crop plants using nitrogen-free bromothymol blue medium with all forming a white subsurface pellicle and they were further screened to seven (7) isolates, based on their morphological, biochemical, and plant growth phytohormones production characteristics, they include A1, A2, A3, A4, A5, A6 and A7. Three of the isolates (A1, A3, and A6) were randomly selected for molecular identification. The Fourier Transform Infrared Spectrophotometer identified the functional groups that are present in the Azospirillum strains to be aromatic compounds. All isolates showed ammonium production potential with A7 having the highest production of 781.3 µg/ml. Only four (4) isolates showed the ability to solubilize Calcium triphosphate with A7 having the highest solubilization (776 µg/ml). Furthermore, all isolates exhibited the ability to produce Indole acetic acids in the growth medium with A6 having the highest production (798.5 µg/ml). The molecular analysis and the sequence analysis of the three isolates 16SrRNA showed two of the isolates to be Azospirillum brasilense (A1, A3) and the other Azospirillum lipoferum (A6). Therefore, this study shows that this strain of Azospirillum has a high ability to produce Indole Acetic Acids, which aids in the production of phytohormones such as Auxins, Solubilize Calcium triphosphate and hence proffer a sustainable solution to improving plant growth.

Azospirillum isscasi sp. nov., a bacterium isolated from rhizosphere soil of rice.

A Gram-negative and rod-shaped bacterium, designated C340-1T, was isolated and screened from paddy soil in Zhongshan County, Guangxi Province, PR China. This strain grew at 20-42 °C (optimum, 37 °C), pH 5.0-9.0 (optimum, pH 7.0) and 0-4 % (w/v) NaCl (optimum, 0-1 %) on Reasoner's 2A medium. The strain could fix atmospheric nitrogen and acetylene reduction activity was recorded up to 120.26 nmol ethylene h-1 (mg protein)-1. Q-10 was the only isoprenoid quinone component; phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, an unidentified aminolipid and an unidentified polar lipid were the major polar lipids. Summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) were the primary cellular fatty acids. The genome of strain C340-1T was 6.18 Mb, and the G+C content was 69.0 mol%. Phylogenetic tree analysis based on 16S rRNA gene and 92 core genes showed that strain C340-1T was closely related to and clustered with the type strains Azospirillum brasilense JCM 1224T, Azospirillum argentinense Az39T, Azospirillum baldaniorum Sp245T and Azospirillum formosense JCM 17639T. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridization (dDDH) values between strain C340-1T and the closely related type strains mentioned above were significantly lower than the threshold values for species classification (95-96 %, 95-96 % and 70 %, respectively). Based on phylogenetic, genomic, phenotypic, physiological and biochemical data, we have reason to believe that C340-1T represents a new species of the genus Azospirillum, for which the name Azospirillum isscasi sp. nov. is proposed. The type strain is C340-1T(=CCTCC AB 2023105T=KCTC 8126T).

In Vitro Screening for Abiotic Stress Tolerance and Biocontrol Ability of Plant Growth Promoting Strains of Azotobacter and Azospirillum spp.

The selection and deployment of microorganisms in stressed ecosystems with biocontrol ability is a major challenge. In this investigation, we sought to isolate and identify strains of Azotobacter and Azospirillum spp., which could withstand abiotic stresses and possess the potential to serve as biological control against five phytopathogenic fungi. Stress tolerance was evidently less obvious in Azospirillum strains than in Azotobacter strains, when bacterial strains were screened for high temperature (50 °C), salt (7% NaCl), and drought (1.2 MPa). Strains Asp30 and Asp 32 of Azospirillum and Azb 19, Azb20 and Azb27 of Azotobacter were found tolerant to temperature, drought and salinity stresses. Five strains of Azotobacter viz. Azb2, Azb6, Azb10, Azb16 and Azb18 and six strains of Azospirillum viz. Asp2, Asp10, Asp22, Asp30, Asp32 and Asp39 inhibited all the five fungal phytopathogens studied. Therefore, in vitro screening provided the basis for identification and selection of strains with abiotic stress tolerance and biocontrol ability.

In silico identification and characterization of nifH protein of Azospirillum strains isolated from Solanum tuberosum L.

Nitrogen (N) constitutes as a fundamental macronutrient necessary for maintaining plant health, metabolism, and overall survival. However, it exists in the soil in insoluble compound forms that plants cannot directly uptake. Biological N-fixation (BNF) is a fundamental process wherein atmospheric N2 is reduced to form biologically available ammonium, providing a key N source for plants. The process of BNF is carried out by a diverse yet limited group of microorganisms termed diazotrophs, using the nitrogenase enzyme. This enzyme complex includes two proteins: di-nitrogenase reductase iron protein (nifH), and di-nitrogenase molybdenum iron protein. Due to its significant conservation, the nifH gene serves as a valuable molecular marker for assessing the potential of N-fixation in various microorganisms. Therefore, the current study focused on a comprehensive computational exploration nifH gene and protein of Azospirillum strains (TN03 and TN22). This analysis includes the evaluation of their physicochemical traits, phylogenetic analysis, structural properties (including 3D models), quality assessment of models, and functional annotation analysis using various established bioinformatics tools. The protein of both strains showed an average molecular weight of approximately 14959 and 15313 Da, respectively, exhibited thermal stability and an acidic profile. Furthermore, this theoretical insight could aid researchers in understanding the structure of predicted protein and might facilitate the designing of genetically modified N-fixing bacteria through the design of specific primers.

Aldehyde Dehydrogenase Diversity in Azospirillum Genomes

Aldehyde dehydrogenases (ALDHs) are indispensable enzymes that play a pivotal role in mitigating aldehyde toxicity by converting them into less reactive compounds. Despite the availability of fully sequenced Azospirillum genomes in public databases, a comprehensive analysis of the ALDH superfamily within these genomes has yet to be undertaken. This study presents the identification and classification of 17 families and 31 subfamilies of ALDHs in fully assembled Azospirillum genomes. This classification system framework provides a more comprehensive understanding of the diversity and redundancy of ALDHs across bacterial genomes, which can aid in elucidating the distinct characteristics and functions of each family. The study also proposes the adoption of the ALDH19 family as a powerful phylogenetic marker due to its remarkable conservation and non-redundancy across various Azospirillum species. The diversity of ALDHs among different strains of Azospirillum can influence their adaptation and survival under various environmental conditions. The findings of this study could potentially be used to improve agricultural production by enhancing the growth and productivity of crops. Azospirillum bacteria establish a mutualistic relationship with plants and can promote plant growth by producing phytohormones such as indole-3-acetic acid (IAA). The diversity of ALDHs in Azospirillum can affect their ability to produce IAA and other beneficial compounds that promote plant growth and can be used as biofertilizers to enhance agricultural productivity.

INFLUÊNCIA DA COINOCULAÇÃO DE SOJA COM Bradyrhizobium E DIFERENTES CEPAS DE Azospirillum EM PARÂMETROS DE FIXAÇÃO BIOLÓGICA DE NITROGÊNIO

The objective was to evaluate the efficiency in parameters of biological nitrogen fixation (BNF) of new strains of Azospirillum for coinoculation with Bradyrhizobium in soybean. For this, a fiel experimentw was set up with the following treatments: 1 - negative control without inoculant; 2 - positive control com 200 kg ha-1 of chemical nitrogen fertilizer; 3- inoculation with Bradyrhizobium (B); 4 -coinoculation of B with Azospirillum brasilense; 5 - coinoculation B + strain 1; 6 - coinoculation B + strain 2; T7 - coinoculation B + strain 3 and 8 - coinoculation B + strains 1, 2 and 3. At flowering, 5 plants were collected per experimental plot. The evaluated parameters were: number and dry mass of nodules on the main root (NMR, DMMR), on the secondary roots (NSR, DMSR) and total (NTR, DMTR); dry mass of aerial part (DMAP) and of the root (DMR). In relation to NSR and NTR, treatment 4 provided a greater increment of nodules in the secondary roots and a total of respectively 25 and 31,87 nodules plant-1 in relation to the others tested. For NMR treatments 3 and 4 were similar with means of 6,7 and 6,87 nodules plant-1, not statistically diferente from treatments with others Azospirillum strains (5, 6 and 7). As for DMMR, DMSR and DMTR, 4 and 3 stood out in relation to these parameters and were superior to treatments (5, 6, 7 and 8). Only for DMR and DMAP chemical nitrogen fertilization (2) stood out statistically, with the first parameter statistically similar to treatment 4 and second to treatment 8. It can be concluded that the new strains did not stand out in the parameters of BNF, with coinoculation with Azospirillum brasilense more efficient. Keywords: Lineage selection, Mixed inoculation, Glycine max.

Azospirillum baldaniorum improves acclimation, lipid productivity and oxidative response of a microalga under salt stress

There is a growing interest in using microalgae for a variety of purposes, including production of pharmaceuticals, wastewater treatment, CO2 capture from flue gases, and biomass as a feedstock for biofuels and feed/food supplements. In addition to environmental conditions, the local availability of suitable water for massive production microalgal biomass often compromises biomass productivity, and thus, techno-economic feasibility towards implementation. Although salinity tends to promote accumulation of carbon reserves in some freshwater microalgae, which could be advantageous for producing feedstocks for biofuels, the negative effect on growth usually off-sets this benefit, and results in a lower productivity of the target. The aim of this study was to analyse whether inoculation with a plant growth-promoting bacterium could ameliorate the detrimental effect of NaCl on growth of a microalga. We showed that inoculation with Azospirillum baldaniorum Sp245 improved the early response of Scenedesmus obliquus CS1 to NaCl addition, and its overall growth performance. As a result, co-cultures attained higher biomass and lipids productivities than microalgal axenic cultures. Lipid productivity raised up due to both: an increased biomass production and a higher lipids enrichment in the biomass. Similar results were obtained under constant light and temperature or under climate-simulated conditions in environmental photobioreactors (Phenometrics™). Inoculation with the bacterium lowered the levels of reactive oxygen species, SH groups, chlorophyll and carotenoids in the algal cells, as well as cell damage, induced by salt stress. Inoculation with Azospirillum strains genetically modified to produce contrasting levels of IAA, suggested that although under non-stress conditions most of the algal growth promotion is IAA-dependent, under salt stress other still-unidentified factor(s) might play a more prominent role in algal stimulation.This study increased the current understanding of the mechanisms underpinning bacterial-microalgal associations, and helps to design alternative strategies to increase algal productivity under suboptimal growth conditions, as most applications demand.

Symbiotic Variations among Wheat Genotypes and Detection of Quantitative Trait Loci for Molecular Interaction with Auxin-Producing Azospirillum PGPR.

Crop varieties differ in their ability to interact with Plant Growth-Promoting Rhizobacteria (PGPR), but the genetic basis for these differences is unknown. This issue was addressed with the PGPR Azospirillum baldaniorum Sp245, using 187 wheat accessions. We screened the accessions based on the seedling colonization by the PGPR and the expression of the phenylpyruvate decarboxylase gene ppdC (for synthesis of the auxin indole-3-acetic acid), using gusA fusions. Then, the effects of the PGPR on the selected accessions stimulating Sp245 (or not) were compared in soil under stress. Finally, a genome-wide association approach was implemented to identify the quantitative trait loci (QTL) associated with PGPR interaction. Overall, the ancient genotypes were more effective than the modern genotypes for Azospirillum root colonization and ppdC expression. In non-sterile soil, A. baldaniorum Sp245 improved wheat performance for three of the four PGPR-stimulating genotypes and none of the four non-PGPR-stimulating genotypes. The genome-wide association did not identify any region for root colonization but revealed 22 regions spread on 11 wheat chromosomes for ppdC expression and/or ppdC induction rate. This is the first QTL study focusing on molecular interaction with PGPR bacteria. The molecular markers identified provide the possibility to improve the capacity of modern wheat genotypes to interact with Sp245, as well as, potentially, other Azospirillum strains.

Metal-Resistant PGPR Strain Azospirillum brasilense EMCC1454 Enhances Growth and Chromium Stress Tolerance of Chickpea (Cicer arietinum L.) by Modulating Redox Potential, Osmolytes, Antioxidants, and Stress-Related Gene Expression.

Heavy metal stress, including from chromium, has detrimental effects on crop growth and yields worldwide. Plant growth-promoting rhizobacteria (PGPR) have demonstrated great efficiency in mitigating these adverse effects. The present study investigated the potential of the PGPR strain Azospirillum brasilense EMCC1454 as a useful bio-inoculant for boosting the growth, performance and chromium stress tolerance of chickpea (Cicer arietinum L.) plants exposed to varying levels of chromium stress (0, 130 and 260 µM K2Cr2O7). The results revealed that A. brasilense EMCC1454 could tolerate chromium stress up to 260 µM and exhibited various plant growth-promoting (PGP) activities, including nitrogen fixation, phosphate solubilization, and generation of siderophore, trehalose, exopolysaccharide, ACC deaminase, indole acetic acid, and hydrolytic enzymes. Chromium stress doses induced the formation of PGP substances and antioxidants in A. brasilense EMCC1454. In addition, plant growth experiments showed that chromium stress significantly inhibited the growth, minerals acquisition, leaf relative water content, biosynthesis of photosynthetic pigments, gas exchange traits, and levels of phenolics and flavonoids of chickpea plants. Contrarily, it increased the concentrations of proline, glycine betaine, soluble sugars, proteins, oxidative stress markers, and enzymatic (CAT, APX, SOD, and POD) and non-enzymatic (ascorbic acid and glutathione) antioxidants in plants. On the other hand, A. brasilense EMCC1454 application alleviated oxidative stress markers and significantly boosted the growth traits, gas exchange characteristics, nutrient acquisition, osmolyte formation, and enzymatic and non-enzymatic antioxidants in chromium-stressed plants. Moreover, this bacterial inoculation upregulated the expression of genes related to stress tolerance (CAT, SOD, APX, CHS, DREB2A, CHI, and PAL). Overall, the current study demonstrated the effectiveness of A. brasilense EMCC1454 in enhancing plant growth and mitigating chromium toxicity impacts on chickpea plants grown under chromium stress circumstances by modulating the antioxidant machinery, photosynthesis, osmolyte production, and stress-related gene expression.

Response of different strains of Azospirillum towards nitrogen fixation and soil respiration on the application of substituted urea herbicides

Response of different strains of Azospirillum towards nitrogen fixation and soil respiration on the application of substituted urea herbicides

Protist–Lactic Acid Bacteria Co-Culture as a Strategy to Bioaccumulate Polyunsaturated Fatty Acids in the Protist Aurantiochytrium sp. T66

Thraustochytrids are aquatic unicellular protists organisms that represent an important reservoir of a wide range of bioactive compounds, such as essential polyunsaturated fatty acids (PUFAs) such as arachidonic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), which are involved in the regulation of the immune system. In this study, we explore the use of co-cultures of Aurantiochytrium sp. and bacteria as a biotechnological tool capable of stimulating PUFA bioaccumulation. In particular, the co-culture of lactic acid bacteria and the protist Aurantiochytrium sp. T66 induce PUFA bioaccumulation, and the lipid profile was evaluated in cultures at different inoculation times, with two different strains of lactic acid bacteria capable of producing the tryptophan dependent auxins, and one strain of Azospirillum sp., as a reference for auxin production. Our results showed that the Lentilactobacillus kefiri K6.10 strain inoculated at 72 h gives the best PUFA content (30.89 mg g-1 biomass) measured at 144 h of culture, three times higher than the control (8.87 mg g-1 biomass). Co-culture can lead to the generation of complex biomasses with higher added value for developing aquafeed supplements.

Degradation of iprodione by a novel strain Azospirillum sp. A1-3 isolated from Tibet.

A bacterial strain A1-3 with iprodione-degrading capabilities was isolated from the soil for vegetable growing under greenhouses at Lhasa, Tibet. Based on phenotypic, phylogenetic, and genotypic data, strain A1-3 was considered to represent a novel species of genus Azospirillum. It was able to use iprodione as the sole source of carbon and energy for growth, 27.96 mg/L (50.80%) iprodione was reduced within 108 h at 25°C. During the degradation of iprodione by Azospirillum sp. A1-3, iprodione was firstly degraded to N-(3,5-dichlorophenyl)-2,4-dioxoimidazolidine, and then to (3,5-dichlorophenylurea) acetic acid. However, (3,5-dichlorophenylurea) acetic acid cannot be degraded to 3,5-dichloroaniline by Azospirillum sp. A1-3. A ipaH gene which has a highly similarity (98.72-99.92%) with other previously reported ipaH genes, was presented in Azospirillum sp. A1-3. Azospirillum novel strain with the ability of iprodione degradation associated with nitrogen fixation has never been reported to date, and Azospirillum sp. A1-3 might be a promising candidate for application in the bioremediation of iprodione-contaminated environments.

Indigenous diazotrophs and their effective properties for organic agriculture

Nitrogen-fixing microorganisms (diazotrophs) converting the atmospheric N2 into usable form NH4 are considered the key players in the nitrogen cycle, chiefly responsible for the enriching nitrogen content in the soils. Globally, biological fixation of N2 greatly contributes to plant growth, lessens the need for chemical fertilizers, and thus contributes to the mitigation of greenhouse gases NOx. In this study, diazotrophic bacterial strains were isolated from rhizosphere soils and root nodules of legume and non-legume plants in Vietnam. Quantitative analyzes by the acetylene reduction assay showed that the isolates have high nitrogen fixation activity compared with that of reference strain Azospirillum vinelandii KCTC 2426. In addition, other effective capabilities of the isolated strains toward supporting agriculture were investigated, i.e. synthesizing IAA and siderophore for promoting plant growth, or producing exopolysaccharides for maintaining soil moisture. Taxonomic positions of the isolated strains were identified based on the comparative analyses of sequences of the 16S rDNA and gene related to nitrogen fixation (nifH), revealing a high taxonomic diversity among free-living and symbiotic diazotrophic isolates. Direct support of the selected isolates to plant growth was proven in experiments with mung beans under laboratory conditions. Thus, the native diazotrophic strains obtained in this study would be good microbial sources for application in organic agriculture and soil amendment.

Исследование влияния солей металлов на активность ферментов фенолоксидазного комплекса бактерий рода Azospirillum

Recently, much attention has been paid to the development of technologies for biodegradation of organopollutants and the search for promising biodestructors. The environmental accumulation of lignin-like compounds and synthetic dyes poses a huge threat not only to ecosystems and biodiversity, but also to human health. Phenol oxidases are enzymes with broad substrate specificity, with oxidizing ability towards various polyphenols and aromatic amines. Therefore the use of phenol oxydases as bioremediation agents is promising due to their unique catalytic properties. In this work we present the results of a study of the effect of metal ions on the activity of the azospirilla phenol oxidase complex. It was demonstrated that extracellular laccases of lignin- and Mn-peroxidases of strains Azospirillum baldaniorum Sp245 and Azospirillum brasilense SR80 are quite stable in the presence of the studied metal salts. The enzymatic activity decreased and the effectiveness of the organopollutants’ biodegradation efficacy was inhibited in the presence of Zn2+ ions. The laccase and lignin-peroxidase activity induced by copper ions positively correlated with the ability of lignin degradation by azospirillum. Analysis of the obtained data showed that inhibitors and inducers of authentic extracellular phenol oxidases of both fungi and bacteria are typical for azospirillum enzymes.

Formulation technology: Macrocystis pyrifera extract is a suitable support/medium for Azospirillum brasilense

Sustainable agricultural strategies include the use of inoculants that enhance plant growth (and therefore yield) through the action of living microorganisms. The extract of Macrocystis pyrifera, the largest and fastest growing macroalgal species, could be a suitable alternative as a support medium for the design of such inoculants, since it may ensure the long-term viability of the microorganisms. Moreover, certain physiological and biochemical aspects of this extract may prove beneficial when applied to plants. This study characterized and analyzed Macrocystis pyrifera in terms of its nutritional and hormonal composition and its metabolomic profile. Formulations made with different extract concentrations were evaluated for their impact on the growth, viability and cell survival of inoculant strain Azospirillum brasilense Az39. The results show that the most promising algae extracts (AE) are those formulated at 3 and 30 %. They contain a variety of mineral nutrients, such as magnesium, calcium, phosphorus, ferrum, zinc and boron. They also have a high concentration of organic matter and a high carbon/nitrogen ratio. These nutrients, as well as the production of phytohormones and compounds derived from alginic acid, promoted bacterial growth and viability in bacterium-algae formulations over a period of twenty-eight days. Several hormones were detected in the pure AE, in Az39 grown in NFb, and in the combinations of both (AE + Az39). Although these hormones (gibberellins, auxins and cytokinins) were found in all the samples, pure AE had the highest gibberellin content. Cytokinin production was additive in the formulations. Moreover, recovery of A. brasilense cells was significant in in vitro and in vivo assays on Zea mays seeds. These findings provide evidence in favor of using algae extracts as a renewable bioresource for the design of eco-friendly and effective inoculants.

Improving the efficacy of potato clonal micropropagation by inoculation with the rhizosphere bacteria Azospirillum baldaniorum Sp245 and Ochrobactrum cytisi IPA7.2.

Sustainable development of agriculture depends on the provision of quality seeds to the market. Inoculation with plant-growth-promoting rhizobacteria in in vitro culture can be used to improve the growth eff icacy and performance of microplants. We examined the effect of in vitro inoculation of microplants of the cultivars Nevsky and Kondor with the strains Azospirillum baldaniorum Sp245 and Ochrobactrum cytisi IPA7.2 separately and in combination. We examined the morphological variables of plant growth in in vitro culture and under ex vitro adaptation conditions; we also investigated the growth and performance of the plants in the greenhouse. The dependence of the inoculation eff icacy on potato genotype, growth stage, and inoculum composition was ascertained throughout the experiment. In vitro, A. baldaniorum Sp245 alone and in combination with O. cytisi IPA7.2 promoted the formation of roots on the microplants of both cultivars and the growth of Nevsky shoots. During plant growth ex vitro, all growth variables of the Nevsky microplants were promoted by O. cytisi IPA7.2 alone and in combination with A. baldaniorum Sp245. In both cultivars grown in the greenhouse, shoot growth was promoted in most inoculation treatments. The survival ability of the Nevsky microplants in the greenhouse increased 1.7-fold under the effect of simultaneous inoculation. Inoculation of microplants with a combination of A. baldaniorum Sp245 and O. cytisi IPA7.2 increased the number of Nevsky minitubers 1.5-fold and the number of Kondor minitubers 3.5-fold. Inoculation with the tested strains can be used to promote the growth of microplants and increase the yield of minitubers in potato seed breeding for the production of healthy planting material.