Enhancing drought stress tolerance and growth promotion in chiltepin pepper (Capsicum annuum var. glabriusculum) through native Bacillus spp

The drought can cause a decrease in food production and loss of biodiversity. In northern Mexico, an arid region, the chiltepin grows as a semi-domesticated crop that has been affected in its productivity and yield. An alternative to mitigate the effect of drought and aid in its conservation could be using Plant Growth-Promoting Bacteria (PGPB). The present study evaluated the capacity of native Bacillus spp., isolated from arid soils, as PGPBs and drought stress tolerance inducers in chiltepin under controlled conditions. Chiltepin seeds and seedlings were inoculated with native strains of Bacillus spp. isolated from arid soils, evaluating germination, vegetative, and drought stress tolerance parameters. The PGPBs improved vegetative parameters such as height, stem diameter, root length, and slenderness index in vitro. B. cereus (Bc25-7) improved in vitro survival of stressed seedlings by 68% at -1.02 MPa. Under greenhouse conditions, seedlings treated with PGPBs exhibited increases in root length (9.6%), stem diameter (13.68%), leaf fresh weight (69.87%), and chlorophyll content (38.15%). Bc25-7 alleviated severe water stress symptoms (7 days of water retention stress), and isolates B. thuringiensis (Bt24-4) and B. cereus (Bc25-7, and Bc30-2) increased Relative Water Content (RWC) by 51%. Additionally, the treated seeds showed improved germination parameters with a 46.42% increase in Germination Rate (GR). These findings suggest that using PGPBs could be an alternative to mitigate the effect of drought on chiltepin.

Drought stress tolerance and metabolomics of Medicago sativa induced by Bacillus amyloliquefaciens DGL1

Introduction

This study used Bacillus amyloliquefaciens DGL1 isolated from the arid sandy land of the Qinghai-Tibetan Plateau as the research strain and investigated the effects of DGL1 on the biomass, physiology, and metabolites of Medicago sativa under different intensities of drought stress to provide a high-quality bacterial source and a theoretical basis for the research and development of biological fertilizer suitable for arid areas.

Methods

The exopolysaccharides (EPS), 1-Aminocyclopropane-1-carboxylate deaminase (ACC), and phosphorus solubilizing capacity of DGL1 were determined. The effects of a DGL1 suspension on alfalfa biomass, physiological indexes, degree of peroxidation of cell membranes, and activity of antioxidant enzymes were determined after irrigating roots under drought stress. The effects on soil physicochemical properties were also evaluated, and metabolomics analysis was performed to explore the effect of DGL1 on the metabolites of alfalfa under drought stress.

Results

Strain DGL1 produced extracellular polysaccharide EPS and ACC deaminase and was capable of phosphorus solubilization. Treatment with DGL1 increased the biomass of alfalfa under different degrees of drought stress, significantly increased the activities of alfalfa antioxidant enzymes Super Oxide Dismutase (SOD), Peroxidase (POD), and catalase (CAT), reduced the content of MDA and H2O2, and increased the content of quick-acting phosphorus, quick-acting potassium, ammonium nitrogen, and nitrate nitrogen in the soil, thus improving soil fertility. Through metabolomics analysis, DGL1 was shown to affect amino acid metabolic pathways, such as arginine, leucine, glutamate, and tyrosine, as well as the levels of energy-providing polysaccharides and lipids, in alfalfa under 15% PEG-6000 drought stress, enhancing alfalfa's capacity to resist drought stress.

Discussion

Strain DGL1 enhances the drought suitability of alfalfa and has the potential for dryland development as a biological agent.

Temperature-regulated metabolites of Serratiamarcescens inhibited reproduction of pinewood nematode Bursaphelenchus xylophilus

The pinewood nematode Bursaphelenchus xylophilus is an invasive and destructive pathogen in forestry. Serratia marcescens AHPC29 was previously found to have nematicidal activity on B. xylophilus. The effect of AHPC29 growth temperature on B. xylophilus inhibition is unknown. Here we show that AHPC29 cultured at 15°C or 25°C, but not 37°C, inhibited B. xylophilus reproduction. Metabolomic analysis found 31 up-regulated metabolites as potential effective substances in this temperature-related difference, with five of them were tested to be effective in inhibiting B. xylophilus reproduction. Among the five metabolites, salsolinol was further verified in bacterial cultures with effective inhibition concentrations. This study found the inhibition of S. marcescens AHPC29 on B. xylophilus reproduction was temperature regulated and the differently expressed metabolites salsolinol played roles in this temperature-regulated effect, which implies the capability of S. marcescens and its metabolites as promising new agents for the management of B. xylophilus.

Biocontrol potential of bacteria belonging to the Bacillus subtilis group against pests and diseases of agricultural interest through genome exploration

The usage of microorganisms as biocontrol agents and biofertilizers has been recommended and recognized as an ecologically correct alternative to maintaining the productivity and safety of crops. Thus, the objectives of this work were to characterize twelve strains belonging to Invertebrate Bacteria Collection of Embrapa Genetic Resources and Biotechnology by molecular, morphological, and biochemical methods and to evaluate the pathogenicity of these strains against pests and diseases of agricultural interest. The morphological characteristic of the strains was performed according to the principles of Bergy's Manual of Systematic Bacteriology. The genomes of the 12 strains were sequenced in Macrogen, Inc. (Seoul, Korea) using the HiSeq2000 and GS-FLX Plus high-performance platforms. In the determination of antibiotic sensibility profiles, disc-diffusion methods (Cefar Diagnótica Ltda) were adopted©. Selective bioassays were carried out with insects of the Lepidoptera (Spodoptera frugiperda, Helicoverpa armigera, and Chrysodeixis includens), Coleoptera (Anthonomus grandis), Diptera (Aedes aegypti) and Hemiptera (Euschistus heros) orders, and with the nematode Caenorhabditis elegans. In addition, the antagonistic action of the phytopathogens Fusarium oxysporum f. sp. vasinfectum and Sclerotinia sclerotiorum against the strains under study, and in vitro assays of phosphate solubilization were also performed. Sequencing of the complete genome of the 12 strains determined that all of them belonged to the Bacillus subtilis sensu lato group. In the strains genome were detected genic clusters responsible for encoding secondary metabolites such as surfactin, iturin, fengycins/plipastatin, bacillomycin, bacillisin, and siderophores. Due to the production of these compounds, there was a survival reduction of the Lepidoptera order insects and a reduction in the phytopathogens mycelial growth. These results show that the species of group B. subtilis s.l. can become promising microbiological alternatives to pest and disease control.

Bioaugmentation potential of inoculum derived from anaerobic digestion feedstock for enhanced methane production using water hyacinth

The utilisation of water hyacinth for production of biogas is considered to be a solution to both its control and the global renewable energy challenge. In this instance, an investigation was conducted to evaluate the potential of water hyacinth inoculum to enhance methane production during anaerobic digestion (AD). Chopped whole water hyacinth (10% (w/v)) was digested to prepare an inoculum consisting mainly of water hyacinth indigenous microbes. The inoculum was incorporated in the AD of freshly chopped whole water hyacinth to set up different ratios of water hyacinth inoculum and water hyacinth mixture with appropriate controls. The results of batch tests with water hyacinth inoculum showed a maximal cumulative volume of 211.67 ml of methane after 29 days of AD as opposed to 88.6 ml of methane generated from the control treatment without inoculum. In addition to improving methane production, inclusion of water hyacinth inoculum reduced the electrical conductivity (EC) values of the resultant digestate, and, amplification of nifH and phoD genes in the digestate accentuates it as a potential soil ameliorant. This study provides an insight into the potential of water hyacinth inoculum to enhance methane production and contribute to the feasibility of the digestate as a soil fertility enhancer.

Unravelling the potential plant growth activity of halotolerant Bacillus licheniformis NJ04 isolated from soil and its possible use as a green bioinoculant on Solanum lycopersicum L

Immensely expanding world population and narrowing arable land for agriculture is a mighty concern faced by the planet at present. One of the major reasons for decline in arable lands is the increased soil salinity, making it unfavourable for crop cultivation. Utilisation of these saline land for agriculture is possible with suitable invention for improving the soil quality. Biofertizers manufactured out of Plant Growth Promoting Rhizobacteria is one such innovation. In the present study, Bacillus licheniformis NJ04 strain was isolated and studied for its halotolerance and other effective plant growth promoting traits. The NJ04 strain was able to tolerate salt up to 10% and highlighted remarkable antifungal activity against common fungal phytopathogens. The preliminary seed germination test in Solanum lycopersicum seeds revealed a significant increase in root length (16.29 ± 0.91 cm) and shoot length (9.66 ± 0.11 cm) of treated plants as compared with the control plants and thereby shows its possible use as a green bioinoculant in agriculture and an ideal candidate to compete with salt stress.

Diversity and Phosphate Solubilization Efficiency of Phosphate Solubilizing Bacteria Isolated from Semi-Arid Agroecosystems of Eastern Kenya

Phosphorus (P) is a major nutrient required for plant growth but it forms complexes with other elements in soil upon application. A cost-effective way of availing P to plants is by use of Phosphate Solubilizing Bacteria (PSB). There is a wide range of PSB suited for diverse agro-ecologies. A large part of Eastern Kenya especially the lower altitude regions are semi-arid with nutrient depleted soils and predominated by low-income smallholders farmers who do not afford costly inorganic fertilizers. To alleviate poor soil nutrition in this agroecosystem, we sought to study the diversity of phosphate solubilizing bacteria and their phosphate solubilization efficiency. The bacteria were selectively isolated in Pikovskaya’s agar media. Bacterial colonies were enumerated as Colony Forming Units and morphological characterization determined by analyzing morphological characteristics. Genetic characterization was determined based on sequencing of 16S rRNA. A total of 71 PSB were isolated and they were placed into 23 morphological groups. Correlation analysis showed a negative correlation between phosphate solubilizing bacteria and the levels of phosphorus, iron, calcium, magnesium and soil pH. Analysis of 16S rRNA sequences revealed that the genetic sequences of the isolates matched the strains from the genera Burkholderia, Pseudomonas, Bacillus, Enterobacter, Pantoea, Paraburkholderia, Cronobacter, Ralstonia, Curtobacterium, and Massilia deposited in NCBI Database. Analysis of Molecular Variance showed that variation within populations was higher than that of among populations. Phosphate solubilization index values ranged between 1.143 and 5.883. Findings on biodiversity of phosphate solubilizing bacteria led to identification of 10 candidate isolates for plant growth improvement and subsequently, bio-fertilizer development.

Isolation, Characterization, and Tea Growth-Promoting Analysis of JW-CZ2, a Bacterium With 1-Aminocyclopropane-1-Carboxylic Acid Deaminase Activity Isolated From the Rhizosphere Soils of Tea Plants

One of the major mechanisms underlying plant growth-promoting rhizobacteria (PGPR) is the lowering of ethylene level in plants by deamination of 1-aminocyclopropane-1-carboxylic acid (ACC) in the environment. In the present study, using ACC as the sole nitrogen source, we screened seven ACC deaminase-producing bacterial strains from rhizosphere soils of tea plants. The strain with the highest ACC deaminase activity was identified as Serratia marcescens strain JW-CZ2. Inoculation of this strain significantly increased shoot height and stem diameter of tea seedlings, displaying significant promotive effects. Besides, S. marcescens strain JW-CZ2 displayed high ACC deaminase activities in wide ranges of ACC concentration, pH, and temperature, suggesting the applicable potential of JW-CZ2 as a biofertilizer. Genome sequencing indicated that clusters of orthologous groups of proteins (COG) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of JW-CZ2 mainly included amino acid transport and metabolism, transcription, carbohydrate transport and metabolism, inorganic ion transport and metabolism, and membrane transport. Moreover, genes in relation to phosphate solubilization, indole acetic acid (IAA) production, and siderophore were observed in the genome of JW-CZ2, and further experimental evidence demonstrated JW-CZ2 could promote solubilization of inorganic phosphate, inhibit growth of pathogenic fungi, and produce IAA and siderophore. These aspects might be major reasons underlying the plant growth-promoting function of JW-CZ2. Overall, this study provides a new S. marcescens strain, which has applicable potential as a promising biofertilizer.

Dual activity of Serratia marcescens Pt-3 in phosphate-solubilizing and production of antifungal volatiles

Background

Soil fertility decline and pathogen infection are severe issues for crop production all over the world. Microbes as inherent factors in soil were effective in alleviating fertility decrease, promoting plant growth and controlling plant pathogens et al. Thus, screening microbes with fertility improving and pathogen controlling properties is of great importance to humans.

Results

Bacteria Pt-3 isolated from tea rhizosphere showed multiple functions in solubilizing insoluble phosphate, promoting plant growth, producing abundant volatile organic compounds (VOCs) and inhibiting the growth of important fungal pathogens in vitro. According to the 16S rRNA phylogenetic and biochemical analysis, Pt-3 was identified to be Serratia marcescens. The solubilizing zone of Pt-3 in the medium of lecithin and Ca3(PO4)2 was 2.1 cm and 1.8 cm respectively. In liquid medium and soil, the concentration of soluble phosphorus reached 343.9 mg.L− 1, and 3.98 mg.kg− 1, and significantly promoted the growth of maize seedling, respectively. Moreover, Pt-3 produced abundant volatiles and greatly inhibited the growth of seven important phytopathogens. The inhibition rate ranged from 75.51 to 100% respectively. Solid phase micro-extraction coupled with gas chromatography tandem mass spectrometry proved that the antifungal volatile was dimethyl disulfide. Dimethyl disulfide can inhibit the germination of Aspergillus flavus, and severely destroy the cell structures under scanning electron microscopy.

Conclusions

S. marcescens Pt-3 with multiple functions will provide novel agent for the production of bioactive fertilizer with P-solubilizing and fungal pathogens control activity.

Sorghum-Phosphate Solubilizers Interactions: Crop Nutrition, Biotic Stress Alleviation, and Yield Optimization

Sweet sorghum [Sorghum bicolor (L.) Moench] is a highly productive, gluten-free cereal crop plant that can be used as an alternative energy resource, human food, and livestock feed or for biofuel-ethanol production. Phosphate fertilization is a common practice to optimize sorghum yield but because of high cost, environmental hazards, and soil fertility reduction, the use of chemical P fertilizer is discouraged. Due to this, the impetus to search for an inexpensive and eco-friendly microbiome as an alternative to chemical P biofertilizer has been increased. Microbial formulations, especially phosphate solubilizing microbiome (PSM) either alone or in synergism with other rhizobacteria, modify the soil nutrient pool and augment the growth, P nutrition, and yield of sorghum. The use of PSM in sorghum disease management reduces the dependence on pesticides employed to control the phytopathogens damage. The role of PSM in the sorghum cultivation system is, however, relatively unresearched. In this manuscript, the diversity and the strategies adopted by PSM to expedite sorghum yield are reviewed, including the nutritional importance of sorghum in human health and the mechanism of P solubilization by PSM. Also, the impact of solo or composite inoculations of biological enhancers (PSM) with nitrogen fixers or arbuscular mycorrhizal fungi is explained. The approaches employed by PSM to control sorghum phytopathogens are highlighted. The simultaneous bio-enhancing and biocontrol activity of the PS microbiome provides better options for the replacement of chemical P fertilizers and pesticide application in sustainable sorghum production practices.

Erythrobacter aureus sp. nov., a plant growth-promoting bacterium isolated from sediment in the Yellow Sea, China

The application of plant growth-promoting (PGP) bacterium in agriculture is expanding rapidly in recent years. With the development of microbial technology, new bacterial species effective in promoting plant growth have been identified. In this study, a PGP bacterium was isolated from marine sediments of the Yellow Sea in China. The confrontation culture test and pot experiments showed that strain YH-07T inhibited the growth of Fusarium oxysporum f. sp. lycopersici (a plant pathogenic fungus), benefiting plant growth and reducing disease incidence of tomato wilt. We used polyphasic approaches including phenotypic, chemotaxonomic and phylogenetic information to determine its taxonomic status. In addition to profiling general features of the YH-07T genome, we identified genes related to PGP traits and genes involved in environmental stress tolerance. Metabolic assays showed that strain YH-07T could produce siderophores, solubilize phosphate, resist to salinity, and grow well within a wide range of temperature and pH, which is a promising PGP bacterium for future agricultural applications. These results provide evidence that strain YH-07T is a novel species of the genus Erythrobacter, for which the name Erythrobacter aureus sp. nov. is proposed. The type strain is YH-07T (= CGMCC 1.16784T = DSM 107319T).

Isolation, identification and plant growth promotion ability of endophytic bacteria associated with lupine root nodule grown in Tunisian soil

The present study aims to characterize nodule endophytic bacteria of spontaneous lupine plants regarding their diversity and their plant growth promoting (PGP) traits. The potential of PGPR inoculation was investigated to improve white lupine growth across controlled, semi-natural and field conditions. Lupinus luteus and Lupinus angustifolius nodules were shown inhabited by a large diversity of endophytes. Several endophytes harbor numerous plant growth promotion traits such as phosphates solubilization, siderophores production and 1-aminocyclopropane-1-carboxylate deaminase activity. In vivo analysis confirmed the plant growth promotion ability of two strains (Paenibacillus glycanilyticus LJ121 and Pseudomonas brenneri LJ215) in both sterilized and semi-natural conditions. Under field conditions, the co-inoculation of lupine by these strains increased shoot N content and grain yield by 25% and 36%, respectively. These two strains Paenibacillus glycanilyticus LJ121 and Pseudomonas brenneri LJ215 are effective plant growth-promoting bacteria and they may be used to develop an eco-friendly biofertilizer to boost white lupine productivity.