N2-fixing Bacteria Research Articles

Contribution of Biofertilizers to Pulse Crops: From Single-Strain Inoculants to New Technologies Based on Microbiomes Strategies.

Pulses provide distinct health benefits due to their low fat content and high protein and fiber contents. Their grain production reaches approximately 93,210 × 103 tons per year. Pulses benefit from the symbiosis with atmospheric N2-fixing bacteria, which increases productivity and reduces the need for N fertilizers, thus contributing to mitigation of environmental impact mitigation. Additionally, the root region harbors a rich microbial community with multiple traits related to plant growth promotion, such as nutrient increase and tolerance enhancement to abiotic or biotic stresses. We reviewed the eight most common pulses accounting for almost 90% of world production: common beans, chickpeas, peas, cowpeas, mung beans, lentils, broad beans, and pigeon peas. We focused on updated information considering both single-rhizobial inoculation and co-inoculation with plant growth-promoting rhizobacteria. We found approximately 80 microbial taxa with PGPR traits, mainly Bacillus sp., B. subtilis, Pseudomonas sp., P. fluorescens, and arbuscular mycorrhizal fungi, and that contributed to improve plant growth and yield under different conditions. In addition, new data on root, nodule, rhizosphere, and seed microbiomes point to strategies that can be used to design new generations of biofertilizers, highlighting the importance of microorganisms for productive pulse systems.

Reduced cadmium toxicity in rapeseed via alteration of root properties and accelerated plant growth by a nitrogen-fixing bacterium

Cd accumulation in crops has become a global environmental problem because it endangers human health. Screening for microorganisms that can reduce Cd accumulation in crops is a possible measure to address this issue. However, success has been limited, and most previous work did not involve bacteria. In the present study, a strain of N-fixing bacteria (Burkholderia spp.) that exhibits high levels of Cd tolerance was screened. The ability of this bacterium to reduce Cd in rapeseed was then assessed in sterile hydroponic and open soil culture systems. In the hydroponic system, the Burkholderia inoculum promoted Cd fixation in rapeseed roots and thus reduced Cd enrichment in aboveground edible tissues (leaves). The mechanisms were related to increased activity of pectin methylesterase in root cell walls, and the transformation of the chemical form of root Cd from “active” (NaCl-extracted) to “inert” (HCl-extracted and residual Cd) states. Additionally, Burkholderia accelerated plant growth, thus shortening the period in which the plant is available for Cd absorption. In the soil culture system, Burkholderia also reduced Cd enrichment in rapeseed leaves in the presence of other microorganisms. Thus, the bacterial strain shows potential for broad application for reducing the accumulation of Cd in crops.

Fate of a biodegradable plastic in forest soil: Dominant tree species and forest types drive changes in microbial community assembly, influence the composition of plastisphere, and affect poly(butylene succinate-co-adipate) degradation

Poly(butylene succinate-co-adipate) (PBSA) degradation and its plastisphere microbiome in cropland soils have been studied; however, such knowledge is limited in the case of forest ecosystems. In this context, we investigated: i) the impact of forest types (conifer and broadleaved forests) on the plastisphere microbiome and its community assembly, ii) their link to PBSA degradation, and iii) the identities of potential microbial keystone taxa. We determined that forest type significantly affected microbial richness (F = 5.26–9.88, P = 0.034 to 0.006) and fungal community composition (R2 = 0.38, P = 0.001) of the plastisphere microbiome, whereas its effects on microbial abundance and bacterial community composition were not significant. The bacterial community was governed by stochastic processes (mainly homogenizing dispersal), whereas the fungal community was driven by both stochastic and deterministic processes (drift and homogeneous selection). The highest molar mass loss was found for PBSA degraded under Pinus sylvestris (26.6 ± 2.6 to 33.9 ± 1.8 % (mean ± SE) at 200 and 400 days, respectively), and the lowest molar mass loss was found under Picea abies (12.0 ± 1.6 to 16.0 ± 0.5 % (mean ± SE) at 200 and 400 days, respectively). Important fungal PBSA decomposers (Tetracladium) and atmospheric dinitrogen (N2)-fixing bacteria (symbiotic: Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium and Methylobacterium and non-symbiotic: Mycobacterium) were identified as potential keystone taxa. The present study is among the first to determine the plastisphere microbiome and its community assembly processes associated with PBSA in forest ecosystems. We detected consistent biological patterns in the forest and cropland ecosystems, indicating a potential mechanistic interaction between N2-fixing bacteria and Tetracladium during PBSA biodegradation.

Effects of Co-Inoculating Saccharomyces spp. with Bradyrhizobium japonicum on Atmospheric Nitrogen Fixation in Soybeans (Glycine max (L.)).

Crop production encounters challenges due to the dearth of nitrogen (N) and phosphorus (P), while excessive chemical fertilizer use causes environmental hazards. The use of N-fixing microbes and P-solubilizing microbes (PSMs) can be a sustainable strategy to overcome these problems. Here, we conducted a greenhouse pot experiment following a completely randomized blocked design to elucidate the influence of co-inoculating N-fixing bacteria (Bradyrhizobium japonicum) and PSMs (Saccharomyces cerevisiae and Saccharomyces exiguus) on atmospheric N2-fixation, growth, and yield. The results indicate a significant influence of interaction on Indole-3-acetic acid production, P solubilization, seedling germination, and growth. It was also found that atmospheric N2-fixation, nodule number per plant, nodule dry weight, straw, and root dry weight per plant at different growth stages were significantly increased under dual inoculation treatments relative to single inoculation or no inoculation treatment. Increased seed yield and N and P accumulation were also noticed under co-inoculation treatments. Soil available N was highest under sole bacterial inoculation and lowest under the control treatment, while soil available P was highest under co-inoculation treatments and lowest under the control treatment. We demonstrated that the co-inoculation of N-fixing bacteria and PSMs enhances P bioavailability and atmospheric N2-fixation in soybeans leading to improved soil fertility, raising crop yields, and promoting sustainable agriculture.

Mutual supply of carbon and nitrogen sources in the co-culture of aerial microalgae and nitrogen-fixing bacteria

This study investigated co-culture for supply of carbon (C) and nitrogen (N) sources by aerial microalgae and N-fixing bacteria. The aerial microalga Coelastrella sp. KGU-HN001 was isolated from the surface of steel signs in Japan. After examining monocultures of the microalga and N-fixing bacterium Rhodobacter sphaeroides, mutual nutrient supply was evaluated in co-culture using a medium without C and N sources. In co-culture under aerobic conditions, the cell number, biomass, total organic C in cells and the total N of cell suspensions increased. Carbohydrate was secreted from the microalga and nitrogenase activity was expressed by the bacterium. Addition of an N source enhanced N fixation in the co-culture. These results indicated that C and N fixation by the microalga and the bacterium occurred under aerobic conditions, and the microorganisms were able to grow by self-supplying nutrients even under nutrient deficiencies.

Application of bio and NPK fertilizer to improve yield soybean and acid sulfate soil properties in Indonesia

In Indonesia, soybean (Glycine max (L.) Merr.) is the second most important staple food with low production compared to the demand. This problem can be overcome by using marginal land such as acid sulfate soil of tidal swampland, however, the optimal application of fertilizer in such soil is minimal. Therefore, this study aims to examine the application of fertilizer in acid sulfate soil in South Kalimantan, Indonesia. It was conducted using a split-plot design with three replicates and the main plot was biofertilizer, which consisted of no-biofertilizer (P1); biofertilizer consortium of decomposer fungi, P-solubilizing bacteria, N-fixing bacteria (P2), and biofertilizer consortium of N-fixing bacteria symbiotic and nonsymbiotic, P-solubilizing bacteria and phytohormone-producing bacteria (P3). Meanwhile, the subplot was NPK fertilizer dosage, consisting of no-fertilizer (A1), dose of 150% (A2), dose of 100% (A3), and dose of 50% (A4) of the recommendation. The results showed that the biofertilizer and NPK fertilization dose did not show an interaction with soil pH and Al3+. The highest N and K nutrient uptake was in P2 at 50% NPK fertilizer dosage, while P in P3 at 150% NPK fertilization dose. The highest soybean yields were obtained in the application of biofertilizer P3 with 150% NPK, i.e., 1.6 t ha-1, followed by the 1.5 t ha-1 in the application of P2 + 50% NPK. This showed that the use of P2 biofertilizer can reduce NPK fertilizer application to 50% in soybean plants in acid soil tidal lands. Furthermore, the application of biofertilizers can increase soybean productivity in acid sulfate soil in Indonesia.

The role of halotolerant N-fixing bacteria on rice agronomic traits on saline soils by path analysis

Nitrogen-fixing bacteria (NFB) play a significant role in saline soil ecosystems. However, little is known about the correlation between NFB application on growth and yield components of rice plants on saline soils. Exploration and experimental methods were performed to obtain the potential of NFB from a rice field in saline soil and reinoculated in a pot experiment. The experiment was arranged as a randomised block design consisting of 8 treatments, namely inoculation application (control and seed treatments with 20 g inoculant/kg of seed) combined with soil application dosage (0, 500, 1 000 and 1 500 g/ha). The results showed that grain yield increased by 43.8–130.6% with seed treatment of 20 g inoculant/kg of seed combined with soil application 500–1 500 g inoculant/ha. Rice yield was affected by multiple variables NFB population, plant height, number of tillers, and grain straw ratio (R2 = 0.926). Path analysis findings showed that the greatest effective contribution (45.45%) yield of rice in saline soil was contributed NFB population. This finding concludes that the application of NFB inoculants as seed treatments and soil applications can serve as an effective as well as the environmentally friendly microbial-based strategy of rice cultivation on saline soil ecosystems.

Denitrification by Bradyrhizobia under Feast and Famine and the Role of the bc1 Complex in Securing Electrons for N2O Reduction.

Rhizobia living as microsymbionts inside nodules have stable access to carbon substrates, but also must survive as free-living bacteria in soil where they are starved for carbon and energy most of the time. Many rhizobia can denitrify, thus switch to anaerobic respiration under low O2 tension using N-oxides as electron acceptors. The cellular machinery regulating this transition is relatively well known from studies under optimal laboratory conditions, while little is known about this regulation in starved organisms. It is, for example, not known if the strong preference for N2O- over NO3- reduction in bradyrhizobia is retained under carbon limitation. Here, we show that starved cultures of a Bradyrhizobium strain with respiration rates 1 to 18% of well-fed cultures reduced all available N2O before touching provided NO3-. These organisms, which carry out complete denitrification, have the periplasmic nitrate reductase NapA but lack the membrane-bound nitrate reductase NarG. Proteomics showed similar levels of NapA and NosZ (N2O reductase), excluding that the lack of NO3- reduction was due to low NapA abundance. Instead, this points to a metabolic-level phenomenon where the bc1 complex, which channels electrons to NosZ via cytochromes, is a much stronger competitor for electrons from the quinol pool than the NapC enzyme, which provides electrons to NapA via NapB. The results contrast the general notion that NosZ activity diminishes under carbon limitation and suggest that bradyrhizobia carrying NosZ can act as strong sinks for N2O under natural conditions, implying that this criterion should be considered in the development of biofertilizers. IMPORTANCE Legume cropped farmlands account for substantial N2O emissions globally. Legumes are commonly inoculated with N2-fixing bacteria, rhizobia, to improve crop yields. Rhizobia belonging to Bradyrhizobium, the microsymbionts of several economically important legumes, are generally capable of denitrification but many lack genes encoding N2O reductase and will be N2O sources. Bradyrhizobia with complete denitrification will instead act as sinks since N2O-reduction efficiently competes for electrons over nitrate reduction in these organisms. This phenomenon has only been demonstrated under optimal conditions and it is not known how carbon substrate limitation, which is the common situation in most soils, affects the denitrification phenotype. Here, we demonstrate that bradyrhizobia retain their strong preference for N2O under carbon starvation. The findings add basic knowledge about mechanisms controlling denitrification and support the potential for developing novel methods for greenhouse gas mitigation based on legume inoculants with the dual capacity to optimize N2 fixation and minimize N2O emission.

Plants Recruit Peptides and Micro RNAs to Regulate Nutrient Acquisition from Soil and Symbiosis.

Plants engage in symbiotic relationships with soil microorganisms to overcome nutrient limitations in their environment. Among the best studied endosymbiotic interactions in plants are those with arbuscular mycorrhizal (AM) fungi and N-fixing bacteria called rhizobia. The mechanisms regulating plant nutrient homeostasis and acquisition involve small mobile molecules such as peptides and micro RNAs (miRNAs). A large number of CLE (CLAVATA3/EMBRYO SURROUNDING REGION-RELATED) and CEP (C-TERMINALLY ENCODED PEPTIDE) peptide hormones as well as certain miRNAs have been reported to differentially respond to the availability of essential nutrients such as nitrogen (N) and phosphorus (P). Interestingly, a partially overlapping pool of these molecules is involved in plant responses to root colonization by rhizobia and AM fungi, as well as mineral nutrition. The crosstalk between root endosymbiosis and nutrient availability has been subject of intense investigations, and new insights in locally or systemically mobile molecules in nutrient- as well as symbiosis-related signaling continue to arise. Focusing on the key roles of peptides and miRNAs, we review the mechanisms that shape plant responses to nutrient limitation and regulate the establishment of symbiotic associations with beneficial soil microorganisms.

Chemical and microbiological characterization of organic supplements and compost used in agriculture

Excessive use of chemical fertilizers in agriculture enhances crop production but it may pose a risk to food quality and soil environment. One alternative to agrochemicals is the natural make organic supplements to supply essential nutrients for crop growth and promote healthy soil function. Therefore, an experimental study was performed to analyze the chemical and microbiological properties of locally produced supplements based on cow dung, such as vermicompost, farmyard manure, Beejamrit, Jeevamrit, and Ghanjeevarmrit. The Jeevamrit and farmyard manure had the lowest pH (4.93) and electrical conductivity (1.73 dS m-1), whereas Ghanjeevamrit and Jeevamrit observed highest values (7.80 and 3.62 dS m-1). Vermicompost had the highest concentrations of total N (1.76%), P (0.77%), K (0.81 %), Fe (398 mg kg-1), Mn (65.9 mg kg-1), Cu (15.5 mg kg-1), and Zn (18.2 mg kg-1). Under Ghanjeevamrit, 35.9 % of the total carbon was found, followed by farmyard manure (34.5 %) and vermicompost (24.1%). The counts of soil heterotrophic bacteria, fungi, actinomycetes, and beneficial microbial diversity such as P solubilizer, and nitrogen (N) fixer were found highest in vermicompost. However, in Jeevamrit there was no growth of actinomycetes and N-fixing bacteria whereas, in Beejamrit preparation except actinomycetes all other microbial growth was visible. Organic supplements such as farmyard manure had the lowest indole acetic acid production (1.66 μg ml-1), while Ghanjeevamrit showed the highest (6.38 μg ml-1). The liquid formulation (Beejamrit and Jeevamrit) indicated more levels of indole acetic acid than the farmyard manure (2.18 and 1.87 times more, respectively). The application of organic supplements had a great role in supplying available nutrients and modulating microbial diversity and plant growth hormone production.

Seasonal changes in total mercury and methylmercury in subtropical decomposing litter correspond to the abundances of nitrogen-fixing and methylmercury-degrading bacteria.

Previous research has found total mercury (THg) and methylmercury (MeHg) levels increase with litterfall decay, thus suggesting litterfall decomposition plays an essential role in the biogeochemical transformation of mercury (Hg). However, it remains unclear how Hg accumulates in the decaying litter, how bacterial taxa networks vary and what roles various microorganisms play during litterfall decomposition, especially nitrogen (N)-fixing, MeHg-degrading and Hg-methylating microbes. Here, we demonstrated as degradation proceeded, a gradually-complex network evolved for litterfall bacteria for the subtropical mixed broadleaf-conifer (MBC) forest, whereas a relatively static network existed for the evergreen broadleaf (EB) forest. N-fixing and MeHg-degrading bacteria dominated throughout litterfall decomposition process, with relative abundances of N-fixing genera and nifH copies maximum and relative abundances of MeHg-degrading bacteria and merAB copies minimum in summer. Hence, N-fixing bacteria likely mediate THg increase in the decomposing litterfall, while MeHg enhancement may be regulated by aerobic MeHg-degrading microbes which can transform MeHg to inorganic divalent Hg (Hg2+) or further to elemental Hg (Hg0). Together, this work elucidates variations of N-fixing and MeHg-degrading microbes in decaying litterfall and their relationships with Hg accumulation, providing novel insights into understanding the biogeochemical cycle of Hg in the forest ecosystem.

Plant species, nitrogen status and endophytes are drivers of soil microbial communities in grasslands

Context There is concern that the introduction of ‘novel’ plant germplasm/traits could outpace our capacity to measure and so assess their impacts on soil microbial communities and function. Aim This study aimed to investigate the effects of plant species/functional traits, nitrogen (N) fertilisation and endophyte infection on grassland soil microbial communities within a short time span of 2 years. Methods Two field experiments with monoculture plots were conducted in a common soil. Experiment 1 compared grasses and legumes, using two cultivars of perennial ryegrass (Lolium perenne) that varied in fructan content, along with the legumes white clover (Trifolium repens) and bird’s-foot trefoil (Lotus pedunculatus) that varied in tannin content. Grass treatments received high and low N application levels. Experiment 2 compared the presence/absence of Epichloë strains in ryegrass, tall fescue (Schedonorus phoenix) and meadow fescue (Schedonorus pratensis). Soil microbial communities were analysed by using high-throughput sequencing of DNA isolated from bulk soil cores. Key results Higher abundance of ligninolytic fungi was found in grass soils and pectinolytic fungi in legume soils. Levels of N fertilisation and fructan in ryegrass had only minor effects on soil fungal communities. By contrast, N fertilisation or fixation had a strong effect on bacterial communities, with higher abundance of nitrifiers and denitrifiers in high-N grass soils and in legume soils than in low-N grass soils. Epichloë affected soil microbiota by reducing the abundance of certain fungal phytopathogens, increasing mycorrhizal fungi and reducing N-fixing bacteria. Conclusions Chemical composition of plant cell walls, which differs between grasses and legumes, and presence of Epichloë in grasses were the main drivers of shifts in soil microbial communities. Implications Impacts of farming practices such as mono- or poly-culture, N fertilisation and presence of Epichloë in grasses on soil microbial communities should be considered in pasture management.

Secondary vegetation succession on the Loess Plateau altered the interaction between arbuscular mycorrhizal fungi and nitrogen-fixing bacteria

Arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (expressing the nifH gene) play an important role in maintaining plant growth and soil function, and the reconstruction and restoration of vegetation and degraded ecosystems should focus on these communities and the links between them. However, little is known about changes in these taxa and their interactions during the natural recovery of abandoned land. Here, we investigated the changes in and interactions between AMF and nifH gene-expressing bacteria in farmland (S1), grassland (S2), shrubland (S3), pioneer forests (S4), and climax forests (S5) as five typical stages of vegetation succession on the Loess Plateau, China. We found that vegetation succession significantly influenced the diversity of AMF and nifH communities. With the progression of secondary succession, the diversity of AMF increased from farmland to pioneer forest communities, and decreased in the climax vegetation, while the diversity of the nifH community first decreased and then gradually increased. The community structures of the AMF and nifH communities differed significantly between the five vegetation types. Specifically, the AMF community structure changed significantly during the later stages of succession, while the N-fixing bacteria community tended to be stable during late succession. The interactions between AMF and nifH bacteria gradually increased from the farmland to shrub stages but tended to weaken from the shrub to climax forest stages. Therefore, the relationships between microbial communities during the early and middle stages of vegetation succession following land abandonment on the Loess Plateau are mainly cooperative and mutually beneficial, while competition likely intensifies during later successional stages. Furthermore, we found that soil microbial biomass, enzyme activity, and total phosphorus content were the main drivers of microbial community changes. Overall, this study complements current understanding of the changes and interrelationships of AMF and N-fixing bacteria during vegetation succession in areas prone to soil erosion, and provides new insights into the natural recovery of degraded ecosystems as driven by soil microbial communities.

Exogenous glucose modulated the diversity of soil nitrogen-related bacteria and promoted the nitrogen absorption and utilisation of peanut

Exogenous carbon (C) not only regulates plant growth but also provides energy for microbes and improves the soil environment. We hypothesised that exogenous C could improve plant growth by affecting the soil environment. Therefore, pot experiments were conducted and peanut cvs. Huayu 22(H) and NN-1(B) were used under three different treatments (the control, single nitrogen (N), and N combined with glucose (CN)). The results showed that the abundance and diversity of N-fixing bacteria are obviously influenced by the C and N, and exogenous C can promote the restoration of microbial diversity. The relative abundances of Burkholderiales were increased under HCN and BCN to 9.8% and 9.5%, respectively, compared to the control (3.9%, 2.5%). The abundance of N fixation bacteria increased mainly due to the soil nutrient change. In comparison with the single N treatment, the addition of the C significantly decreased the soil NH4+-N and NO3–-N contents by 31.0% and 13.3%, respectively. And the activities of soil urease and nitrogenase were significantly increased. Compared to the control, single N significantly limited the root development, while the addition of C played a promoting role in root growth. Plant N accumulation increased compared with the control, but there was no significant difference between N treatment and CN treatment. These results indicated that exogenous C promoted soil microorganism activity and strengthened plant growth by changing the soil environment.

Analysis of Bacterial Microbiota of Aerated Compost Teas and Effect on Tomato Growth.

Mature composts and their water-based extracts, known as aerated compost teas (ACTs), are biofertilizers that share bioactive effects like soil restoration and plant health promotion, widely used for sustainable agriculture. Bioactive effects of compost and ACTs could be associated with their physicochemical and biological characteristics, like carbon/nitrogen (C/N) ratio and microbiota structure respectively. In our study, we elaborated ACTs using mature homemade compost, wheat bran, and grass clippings, following the C/N ratio criteria. Irrigation of tomato plantlets with ACT whose C/N ratio was close to the expected C/N ratio for mature compost evidenced plant growth promotion. Exploring the bacterial microbiota of elaborated ACTs and origin compost revealed significant structural differences, including phyla involved in N mineralization and free-living N-fixing bacteria. Therefore, ACTs harbor diverse bacterial microbiota involved in the N cycle, which would enrich plant and soil bacterial communities at the taxonomic and functional levels. Furthermore, ACTs are considered a part of agroecological and circular economy approaches.

Fe-Based Nanomaterial-Induced Root Nodulation Is Modulated by Flavonoids to Improve Soybean (Glycine max) Growth and Quality.

Innovative technology to increase efficient nitrogen (N) use while avoiding environmental damages is needed because of the increasing food demand of the rapidly growing global population. Soybean (Glycine max) has evolved a complex symbiosis with N-fixing bacteria that forms nodules to fix N. Herein, foliar application of 10 mg L-1 Fe7(PO4)6 and Fe3O4 nanomaterials (NMs) (Fe-based NMs) promoted soybean growth and root nodulation, thus improving the yield and quality over that of the unexposed control, EDTA-control, and 1 and 5 mg L-1 NMs. Mechanistically, flavonoids, key signaling molecules at the initial signaling steps in nodulation, were increased by more than 20% upon exposure to 10 mg L-1 Fe-based NMs, due to enhanced key enzyme (phenylalanine ammonia-lyase, PAL) activity and up-regulation of flavonoid biosynthetic genes (GmPAL, GmC4H, Gm4CL, and GmCHS). Accumulated flavonoids were secreted to the rhizosphere, recruiting rhizobia for colonization. Fe7(PO4)6 NMs increased Allorhizobium by 87.3%, and Fe3O4 NMs increased Allorhizobium and Mesorhizobium by 142.2% and 34.9%, leading to increased root nodules by 50.0% and 35.4% over the unexposed control, respectively. Leghemoglobin content was also noticeably improved by 8.2-46.5% upon Fe-based NMs. The higher levels of nodule number and leghemoglobin content resulted in enhanced N content by 15.5-181.2% during the whole growth period. Finally, the yield (pod number and grain biomass) and quality (flavonoids, soluble protein, and elemental nutrients) were significantly increased more than 14% by Fe-based NMs. Our study provides an effective nanoenabled strategy for inducing root nodules to increase N use efficiency, and then both yield and quality of soybean.

Isolation and molecular identification of halotolerant diazotrophic bacteria from The Northern Coastal of Pemalang, Central Java, Indonesia

Abstract. Purwanto, Oktaviani E, Leana NWA. 2022. Isolation and molecular identification of halotolerant diazotrophic bacteria from The Northern Coastal of Pemalang, Central Java, Indonesia. Biodiversitas 23: 5814-5821. Plant Growth Promoting Bacteria can fix nitrogen, a very important macronutrient for plant growth. However, the application of urea as a source of this macronutrient has a negative impact on the environment. Therefore, developing biofertilizers using N-fixing bacteria is an environmentally friendly technology. Therefore, this research aimed to isolate and analyze the diversity of N2-fixing bacteria from saline rice fields. The soil samples were taken from the rhizosphere of rice plants in Nyamplung Sari Village, Petarukan District, Pemalang Regency. Meanwhile, 9 (nine) isolates of nitrogen-fixing bacteria have been isolated, which can fix N2. The isolates can bind to N2, but only a few can produce IAA. The nitrogen-fixing ability of diazotrophic bacteria ranged from 17.85 ppm to 29.05 ppm. Isolate Jn3 has the highest ability to fix nitrogen, reaching 29.05 ppm, while Jn3, J, J12, J5, Kn1, and A3 can produce IAA with values of 2.00, 2.69, 2.22, 1.76, 3.47, and 1.79 ppm, respectively. Based on the 16S rRNA analysis and phylogeny construction, the isolated bacteria were identified in 3 (three) clusters. The first cluster was identified as Pseudomonas stutzeri and Acinetobacter junii (Kn1 and Jn3), while the second was identified as Bacillus cereus, Bacillus tropicus, Bacillus altitudinis, and Bacillus subtilis (Jn, Jn1, A3, and K3 isolates). The third cluster was identified as Bacillus pumilus, Acinetobacter baumanii, and Acinetobacter schindleri (J12, J5, and J). In addition, our study reported the findings of Acinetobacter baumannii and Acinetobacter schindleri species that can fix nitrogen.

Nitrogen-fixing symbiotic bacteria act as a global filter for plant establishment on islands

Island biogeography has classically focused on abiotic drivers of species distributions. However, recent work has highlighted the importance of mutualistic biotic interactions in structuring island floras. The limited occurrence of specialist pollinators and mycorrhizal fungi have been found to restrict plant colonization on oceanic islands. Another important mutualistic association occurs between nearly 15,000 plant species and nitrogen-fixing (N-fixing) bacteria. Here, we look for evidence that N-fixing bacteria limit establishment of plants that associate with them. Globally, we find that plants associating with N-fixing bacteria are disproportionately underrepresented on islands, with a 22% decline. Further, the probability of N-fixing plants occurring on islands decreases with island isolation and, where present, the proportion of N-fixing plant species decreases with distance for large, but not small islands. These findings suggest that N-fixing bacteria serve as a filter to plant establishment on islands, altering global plant biogeography, with implications for ecosystem development and introduction risks.

THE EFFECTIVENESS OF MULTIPLE INOCULATION OF BIODIVERSITY IN IMPROVING SOIL BIOLOGICAL PROPERTIES AND RESULTS OF TWO GOGO RICE VARIETIES IN COASTAL AREA

This study aims to obtain a combination of biological fertilizers and upland rice varieties that can improve soil biological properties and increase upland rice production in coastal areas. This research was conducted from September to December 2019, in Beringin Raya Village, Muara Bangkahulu District, Bengkulu City. Soil and plant analysis were carried out at the Soil Science Laboratory, Faculty of Agriculture, Bengkulu University. This study used a Completely Randomized Block Design (RAKL). The first factor tested was upland rice varieties consisting of Inpago 10 and Serantan. Furthermore, the second factor is the type of biological fertilizer which consists of control, a combination of P solubilizing bacteria, K solubilizing bacteria, and N2 fixing bacteria, as well as a combination of arbuscular mycorrhizal fungi, K solubilizing bacteria, and N2 fixing bacteria. Each treatment combination was repeated 4 times so that there were 24 experimental units. Each experiment consisted of 50 plants so that the total plant population was 50 x 24 = 1,200 plants. The results showed that the combination of double inoculants of biological fertilizers BPF + BPK + BPN and rice variety Inpago 10 resulted in the highest population of potassium solubilizing bacteria, plant dry weight and weight of pithy grain per clump. Double inoculants of BPF + BPK + BPN biofertilizers resulted in the highest population of potassium solubilizing bacteria, the heaviest plant dry weight and weight of pithy grain per clump. Inpago 10 variety also had a higher population of potassium solubilizing bacteria, and better growth and yield components of rice compared to the serantan variety.

Characteristics of bacterial and fungal communities and their impact during cow manure and agroforestry biowaste co-composting

Microbial communities and environmental conditions are both of great importance for efficient utilization of agroforestry resources. Nevertheless, knowledge about the role of soluble nutrients and enzymatic properties, and their inner links with microbial communities remain limited. This is especially the case for the co-composting of agricultural and forestry biowaste. Here, we investigate the succession of key microbes during co-composting (sawdust + cow manure, SA; straw + cow manure, ST), employing amplicon sequencing, enzyme assays, and physicochemical analyses. N-fixing bacteria (Pseudomonas) and C-degrading fungi (Acaulium) have been identified as dominant taxa during such co-composting. Although eight antibiotic resistance genes were found to persist during composting, pathogenic microbes declined with composting time. NO3−-N content was screened as a determinant structuring the bacterial and fungal communities, with importance also shown for C-degrading enzymes such as cellulose, laccase, and peroxidase activity.These results identify the key microbial taxa and their main interactive environmental factors, which are potentially valuable for the development of a mixed microbial inoculant to accelerate the maturation of agroforestry biowastes composting.