Biosynthesis of Cyclic Lipopeptides by Bacillus velezensis Bs006 and its Antagonistic Activity are Modulated by the Temperature and Culture Media Conditions.

Antagonistic activity of strains from Bacillus species has made them among the preferred agricultural biological control agents against phytopathogenic fungi. These microorganisms' success is mostly based on the production of antagonistic secondary metabolites, mainly those of the non-ribosomal cyclic lipopeptides (CLPs) nature, which can affect phytopathogens directly (iturins and fengycins) or indirectly (surfactins and fengycins). However, abiotic factors in the target site can influence the behavior of the biocontrol traits, but to date, few studies attempting to decipher this kind of interaction have been conducted. This work aimed to evaluate the effect of temperature and culture medium on growth, antagonistic activity against Fusarium oxysporum f. sp. physali (Foph), and the profile of CLPs produced by Bacillus velezensis Bs006. The data showed that measured traits in Bs006 varied with temperature and medium interaction. The concentration of CLPs, as well as the antagonistic activity against Foph, was increased as the nutritional wealth, temperature, and time of incubation increased. The concentration of fengycins and iturins was higher than surfactins at high temperatures. However, a bacteriostatic effect was detected with a combination of Landy medium and 15 °C, which prevented both the biosynthesis of CLPs and the antagonistic activity. The results of this work highlight the importance of abiotic conditions of the target site where a biocontrol agent will be applied to stay active and develop its full antagonistic potential. This response by Bs006 could partly explain the variability of its biocontrol efficacy in the Foph-golden berry pathosystem.

Combined Use of PGPRs and Reduced Rates of Azoxystrobin to Improve Management of Sheath Blight of Rice.

Farmers rely heavily on the use of strobilurin fungicides to manage sheath blight (ShB) caused by Rhizoctonia solani AG1-IA, the most important disease in rice in the southern United States. Greenhouse and field studies were conducted to evaluate the potential use of plant growth-promoting rhizobacteria (PGPRs) in combination with a reduced rate of azoxystrobin application as a strategy to improve the current fungicide-reliant management. Of the nine antagonistic PGPR strains screened in the greenhouse, Bacillus subtilis strain MBI600 provided the most significant and consistent suppression of ShB. Efficacy of strain MBI600 was further evaluated at the concentrations of 0, 103, 106, 109, and 1011 CFU/ml alone or in combinations with 0, 17, 33, 50, 67, 83, and 100% of the recommended application rate (0.16 kg a.i./ha) of azoxystrobin. Strain MBI600 applied at 106,109, and 1011 CFU/ml alone was effective in reducing ShB severity. Combinations of this strain at these rates with ≥33% of the recommended application rate of azoxystrobin further reduced ShB severity. A dose-response model defining the relationships between strain MBI600, azoxystrobin, and ShB severity was established. Estimates of the effective concentrations (EC50 and EC90) of strain MBI600 when applied in combination with 50% of the recommended application rate of azoxystrobin were 104 and 109 CFU/ml, respectively. A field trial was conducted over 4 years to verify the efficacy of their combinations. Strain MBI600 alone, when applied at 109 CFU/ml at the boot stage, reduced ShB severity but did not significantly increase grain yields each year. Combination of strain MBI600 with azoxystrobin at half of the recommended application rate improved efficacy of strain MBI600, reducing ShB severity to a level comparable to that of azoxystrobin applied at the full rate in all 4 years. The combined treatment also increased grain yield by 14 to 19%, comparable to the fungicide applied at the full rate in 3 of 4 years. Combined use of PGPR strain MBI600 with a reduced rate of azoxystrobin application can be a viable management option for control of ShB while allowing producers to use less fungicide on rice.

Enhanced biological control of root-knot nematode, Meloidogyne incognita, by combined inoculation of cotton or soybean seeds with a plant growth-promoting rhizobacterium and pectin-rich orange peel.

LC-MS analysis of plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis AP203 supernatants indicated the presence of nematode-inhibiting compounds that increased in abundance when B. velezensis AP203 was grown on orange peel. Meloidogyne incognita J2 were incubated with B. velezensis AP203 spores and orange peel, spores alone, orange peel alone, or with a non-inoculated control, and the combination of B. velezensis AP203 with orange peel resulted in 94% mortality of M. incognita juveniles (p ≤ 0.05). The J2 mortality rate for B. velezensis alone was 53%, compared to 59% mortality with orange peel, and the non-inoculated control exhibited 7% mortality. When tested on soybeans raised in a greenhouse, it was observed that when grown in the presence of orange peel, B. velezensis AP203 culture broth, cell suspension or supernatant reduced the numbers of M. incognita eggs per g of root at 45 days after planting (DAP) compared to inoculated controls in soybean and cotton (p ≤ 0.05). Likewise, soybean root length and fresh root weight significantly increased after inoculation with B. velezensis AP203 amended with orange peel. In cotton, shoot and root length significantly increased after inoculation with cell pellets of B. velezensis AP203 amended with orange peel compared to the M. incognita inoculated control. These data indicate that B. velezensis AP203 responds to growth on pectin-rich orange peel by production of biologically active secondary metabolites that can promote plant growth and inhibit root-knot nematode viability.

Plant-microbe-soil fertility interaction impacts performance of a Bacillus-containing bioproduct on bell pepper.

Limited information is available on the performance of plant growth-promoting inoculants or bioproducts under different soil nutritional or fertility conditions. Consequently, the objective of this study was to evaluate the effects of a commercially available Bacillus-containing bioproduct, Microlife Abundance, at concentrations of 5.5 and 6.5 log cfu/ml on early growth, fertilizer use-efficiency, and fruit yield of bell pepper (Capsicum annuum L.) under two different soil fertility conditions (25% and 100% recommended N rates). Two pot experiments were conducted with bell pepper: (a) a 4-week-long early growth test with inoculant treatments applied once at transplanting; and (b) a 13-week-long yield test with inoculant treatments applied at transplanting and again at first blossom-set. Results from the early growth test indicated that at both N fertilization levels, applying Abundance once at transplanting at 6.5 log cfu/ml rather than 5.5 log cfu/ml significantly increased root dry weight, total root length, root volume, root surface area, and total length of very fine roots compared with the noninoculated control by 20%, 13%, 17%, 15%, and 12%, respectively. In contrast to the early growth, results from the yield test showed that only at the 100% recommended N rate, applying Abundance twice at both concentrations significantly enhanced N fertilizer use-efficiency and marketable yield of bell pepper over the noninoculated control by 34% (5.5 log cfu/ml) and 30% (6.5 log cfu/ml). Therefore, the efficacy of the Bacillus-containing bioproduct Abundance in enhancing fertilizer use-efficiency and marketable yield of bell pepper varied between soil nutritional conditions, but the early growth promotion effect of Abundance did not. Our results also demonstrate that selected microbial-based bioproducts, like Abundance, can be compatible with chemical fertilizers to enhance fertilizer use-efficiency and crop yields, but cannot be used as complete substitutes for chemical fertilizers.

Filibacter tadaridae sp. nov., isolated from within a guano pile from a colony of Mexican free-tailed bats Tadarida brasiliensis.

A Gram-stain-positive, aerobic bacterium, TB-66T, was isolated from a pile of bat guano in a cave of New Mexico, USA. On the basis of 16S rRNA gene sequence similarity comparisons, strain TB-66Tgrouped together with Filibacter limicola showing a 16S rRNA gene sequence similarity of 98.5 % to the type strain. The quinone system of strain TB-66T consisted predominantly of menaquinone MK-7. The polar lipid profile contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylserine and three unidentified phospholipids. The peptidoglycan type was A4α l-Lys-d-Glu (A11.33). The major fatty acids were C15 : 0 anteiso, C16 : 0, and C16 : 1 ω7c. The G+C content of the genomic DNA was 37.6 (±1.8) mol%. On the basis of the genotypic and phenotypic properties it is clear that strain TB-66T represents a member of the genus Filibacter, but is distinct from the only other species in the genus, Filibacter limicola DSM 13886T. We propose a novel species with the name Filibacter tadaridae sp. nov. The type strain is TB-66T (= CIP 111629T= LMG 30660T= CCM 8866T).

Mixtures of Plant-Growth-Promoting Rhizobacteria Enhance Biological Control of Multiple Plant Diseases and Plant-Growth Promotion in the Presence of Pathogens.

Several studies have shown that mixtures of plant-growth-promoting rhizobacteria (PGPR) could enhance biological control activity for multiple plant diseases through the mechanisms of induced systemic resistance or antagonism. Prior experiments showed that four individual PGPR strains-AP69 (Bacillus altitudinis), AP197 (B. velezensis), AP199 (B. velezensis), and AP298 (B. velezensis)-had broad-spectrum biocontrol activity via antagonism in growth chambers against two foliar bacterial pathogens (Xanthomonas axonopodis pv. vesicatoria and Pseudomonas syringae pv. tomato) and one of two tested soilborne fungal pathogens (Rhizoctonia solani and Pythium ultimum). Based on these findings, the overall hypothesis of this study was that a mixture of two individual PGPR strains would exhibit better overall biocontrol and plant-growth promotion than the individual PGPR strains. Two separate greenhouse experiments were conducted. In each experiment, two individual PGPR strains and their mixtures were tested for biological control of three different diseases and for plant-growth promotion in the presence of the pathogens. The results demonstrated that the two individual PGPR strains and their mixtures exhibited both biological control of multiple plant diseases and plant-growth promotion. Overall, the levels of disease suppression and growth promotion were greater with mixtures than with individual PGPR strains.

Isolation and characterization of N2 -fixing bacteria from giant reed and switchgrass for plant growth promotion and nutrient uptake.

The aims of this study were to isolate and characterize N2 -fixing bacteria from giant reed and switchgrass and evaluate their plant growth promotion and nutrient uptake potential for use as biofertilizers. A total of 190 bacteria were obtained from rhizosphere soil and inside stems and roots of giant reed and switchgrass. All the isolates were confirmed to have nitrogenase activity, 96.9% produced auxin, and 85% produced siderophores. Then the top six strains, including Sphingomonas trueperi NNA-14, Sphingomonas trueperi NNA-19, Sphingomonas trueperi NNA-17, Sphingomonas trueperi NNA-20, Psychrobacillus psychrodurans NP-3, and Enterobacter oryzae NXU-38, based on nitrogenase activity, were inoculated on maize and wheat seeds in greenhouse tests to assess their potential benefits to plants. All the selected strains promoted plant growth by increasing at least one plant growth parameter or increasing the nutrient concentration of maize or wheat plants. NNA-14 outperformed others in promoting early growth and nutrient uptake by maize. Specifically, NNA-14 significantly increased root length, surface area, and fine roots of maize by 14%, 12%, and 17%, respectively, and enhanced N, Ca, S, B, Cu, and Zn in maize. NNA-19 and NXU-38 outperformed others in promoting both early growth and nutrient uptake by wheat. Specifically, NNA-19 significantly increased root dry weight and number of root tips of wheat by 25% and 96%, respectively, and enhanced Ca in wheat. NXU-38 significantly increased root length, surface area, and fine roots of wheat by 21%, 13%, and 26%, respectively, and enhanced levels of Ca and Mg in wheat. It is concluded that switchgrass and giant reed are colonized by N2 -fixing bacteria that have the potential to contribute to plant growth and nutrient uptake by agricultural crops.

Paenibacillus nebraskensis sp. nov., isolated from the root surface of field-grown maize.

A Gram-positive-staining, aerobic, non-endospore-forming bacterial strain (JJ-59T), isolated from a field-grown maize plant in Dunbar, Nebraska in 2014 was studied by a polyphasic approach. Based on 16S rRNA gene sequence similarity comparisons, strain JJ-59T was shown to be a member of the genus Paenibacillus, most closely related to the type strains of Paenibacillus aceris (98.6 % 16S rRNA gene sequence similarity) and Paenibacillus chondroitinus (97.8 %). For all other type strains of species of the genus Paenibacillus lower 16S rRNA gene sequence similarities were obtained. DNA-DNA hybridization values of strain JJ-59T to the type strains of P. aceris and P. chondroitinus were 26 % (reciprocal, 59 %) and 52 % (reciprocal, 59 %), respectively. Chemotaxonomic characteristics such as the presence of meso-diaminopimelic acid in the peptidoglycan, the major quinone MK-7 and spermidine as the major polyamine were in agreement with the characteristics of the genus Paenibacillus. Strain JJ-59T shared with its next related species P. aceris the major lipids diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified aminophospholipid, but the presence/absence of certain lipids was clearly distinguishable. Major fatty acids of strain JJ-59T were anteiso-C15 : 0, iso-C15 : 0 and iso-C16 : 0, and the genomic G+C content is 47.2 mol%. Physiological and biochemical characteristics of strain JJ-59T were clearly different from the most closely related species of the genus Paenibacillus. Thus, strain JJ-59T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus nebraskensis sp. nov. is proposed, with JJ-59T (=DSM 103623T=CIP 111179T=LMG 29764T) as the type strain.

Bacillus zeae sp. nov., isolated from the rhizosphere of Zea mays.

A Gram-positive-staining, aerobic organism, isolated from the rhizosphere of Zea mays, was investigated in detail. Based on 16S rRNA gene sequence similarity comparisons, strain JJ-247T was grouped into the genus Bacillus, most closely related to Bacillus foraminis (98.4 %). The 16S rRNA gene sequence similarity to the sequences of the type strains of other species of the genus Bacillus was <97.4 %. The fatty acid profile with the major fatty acids, anteiso-C15 : 0, iso-C15 : 0, iso-C14 : 0 and iso-C16 : 0 supported the grouping of the strain to the genus Bacillus. The polar lipid profile contained the major components diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified aminophospholipid. The major quinone was menaquinone MK-7, and the major polyamine was spermidine. The genomic DNA G+C content of strain JJ-247T was 44.5 mol%. DNA-DNA hybridizations with the type strain B. foraminis LMG 23147T resulted in values below 70 %. In addition, physiological and biochemical test results allowed a clear phenotypic differentiation of strain JJ-247T from B. foraminis. As a consequence, JJ-247T represents a novel species of the genus Bacillus, for which we propose the name Bacillus zeae sp. nov., with JJ-247T (=CCM 8726T=LMG 29876T) as the type strain.

Paenibacillus rhizoplanae sp. nov., isolated from the rhizosphere of Zea mays.

A Gram-stain-positive, aerobic, endospore-forming bacterial strain isolated from the rhizosphere of Zea mays was studied to determine its detailed taxonomic position. Based on 16S rRNA gene sequence similarity comparisons, strain JJ-64T was shown to be a member of the genus Paenibacillus, most closely related to the type strains of Paenibacillus silagei (99 %) and Paenibacillus borealis (97.5 %). 16S rRNA gene sequence similarity to all other Paenibacillus species was ≤97.5 %. DNA-DNA hybridization values to the type strains of P. silagei and P. borealis were 51 % (reciprocal 25 %) and 31 % (reciprocal 37 %), respectively. The presence of meso-diaminopimelic acid as the diagnostic diamino acid of the peptidoglycan, the major quinone MK-7 and the polyamine pattern with spermidine as the major component were well in line with the characteristics of the genus Paenibacillus. Furthermore, the polar lipid profile of strain JJ-64T with the predominant lipids diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylserine and two unidentified aminophospholipids reflected the close phylogenetic relatedness to P. silagei. Major fatty acids were iso- and anteiso-branched components. Physiological and biochemical characteristics allowed the further phenotypic differentiation of strain JJ-64T from the most closely related species. Thus, strain JJ-64T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus rhizoplanae sp. nov. is proposed. The type strain is JJ-64T (=LMG 29875T=CCM 8725T).

Selection and Assessment of Plant Growth-Promoting Rhizobacteria for Biological Control of Multiple Plant Diseases.

A study was designed to screen individual strains of plant growth-promoting rhizobacteria (PGPR) for broad-spectrum disease suppression in vitro and in planta. In a preliminary screen, 28 of 196 strains inhibited eight different tested pathogens in vitro. In a secondary screen, these 28 strains showed broad spectrum antagonistic activity to six different genera of pathogens, and 24 of the 28 strains produced five traits reported to be related to plant growth promotion, including nitrogen fixation, phosphate solubilization, indole-3-acetic acid production, siderophore production, and biofilm formation. In advanced screens, the 28 PGPR strains selected in vitro were tested in planta for biological control of multiple plant diseases including bacterial spot of tomato caused by Xanthomonas axonopodis pv. vesicatoria, bacterial speck of tomato caused by Pseudomonas syringae pv. tomato, damping-off of pepper caused by Rhizoctonia solani, and damping-off of cucumber caused by Pythium ultimum. In all, 5 of the 28 tested strains significantly reduced three of the four tested diseases, and another 19 strains showed biological control to two tested diseases. To understand the observed broad-spectrum biocontrol capacity, antiSMASH was used to predict secondary metabolite clusters of selected strains. Multiple gene clusters encoding for secondary metabolites, e.g., bacillibactin, bacilysin, and microcin, were detected in each strain. In conclusion, selected individual PGPR strains showed broad-spectrum biocontrol activity to multiple plant diseases.

Biological Control of Meloidogyne incognita by Spore-forming Plant Growth-promoting Rhizobacteria on Cotton.

In the past decade, increased attention has been placed on biological control of plant-parasitic nematodes using various fungi and bacteria. The objectives of this study were to evaluate the potential of 662 plant growth-promoting rhizobacteria (PGPR) strains for mortality to Meloidogyne incognita J2 in vitro and for nematode management in greenhouse, microplot, and field trials. Results indicated that the mortality of M. incognita J2 by the PGPR strains ranged from 0 to 100% with an average of 39%. Among the PGPR strains examined, 212 of 662 strains (or 33%) caused significantly greater mortality percent of M. incognita J2 than the untreated control. Bacillus was the major genus initiating a greater mortality percentage when compared with the other genera. In subsequent trials, B. velezensis strain Bve2 reduced M. incognita eggs per gram of cotton root in the greenhouse trials at 45 days after planting (DAP) similarly to the commercial standards Abamectin and Clothianidin plus B. firmus I-1582. Bacillus mojavensis strain Bmo3, B. velezensis strain Bve2, B. subtilis subsp. subtilis strain Bsssu3, and the Mixture 2 (Abamectin + Bve2 + B. altitudinis strain Bal13) suppressed M. incognita eggs per gram of root in the microplot at 45 DAP. Bacillus velezensis strains Bve2 and Bve12 also increased seed-cotton yield in the microplot and field trials. Overall, results indicate that B. velezensis strains Bve2 and Bve12, B. mojavensis strain Bmo3, and Mixture 2 have potential to reduce M. incognita population density and to enhance growth of cotton when applied as in-furrow sprays at planting.

Rhizobacteria activates (+)-δ-cadinene synthase genes and induces systemic resistance in cotton against beet armyworm (Spodoptera exigua).

Gossypol is an important allelochemical produced by the subepidermal glands of some cotton varieties and important for their ability to respond to changing biotic stress by exhibiting antibiosis against some cotton pests. Plant growth-promoting rhizobacteria (PGPR) are root-colonizing bacteria that increase plant growth and often elicit defence against plant pathogens and insect pests. Little is known about the effect of PGPR on cotton plant-insect interactions and the potential biochemical and molecular mechanisms by which PGPR enhance cotton plant defence. Here, we report that PGPR (Bacillus spp.) treated cotton plants showed significantly higher levels of gossypol compared with untreated plants. Similarly, the transcript levels of the genes (i.e. (+)-δ-cadinene synthase gene family) involved in the biosynthesis of gossypol were higher in PGPR-treated plants than in untreated plants. Furthermore, the levels of jasmonic acid, an octadecanoid-derived defence-related phytohormone and the transcript level of jasmonic acid responsive genes were higher in PGPR-treated plants than in untreated plants. Most intriguingly, Spodoptera exigua showed reduced larval feeding and development on PGPR-treated plants. These findings demonstrate that treatment of plants with rhizobacteria may induce significant biochemical and molecular changes with potential ramifications for plant-insect interactions.

Bacillus cucumis sp. nov. isolated from the rhizosphere of cucumber (Cucumis sativus).

A facultative anaerobic, Gram-positive staining, endospore-forming bacterium, isolated from the rhizosphere of cucumber (Cucumis sativus), was taxonomically investigated. Based on 16S rRNA gene sequence similarity comparisons, strain AP-6T clustered together with other species of the genus Bacillus and showed highest similarities with Bacillus drentensis LMG 21831T (99.1 %), Bacillus vireti LMG 21834T (98.7 %) and Bacillus soli LMG 21838T (98.5 %). The 16S rRNA gene sequence similarity to the sequences of the type strains of other species of the genus Bacillus was 98.5 % or less. Chemotaxonomic features supported the grouping of the strain in the genus Bacillus; for example, the major fatty acids were anteiso-C15 : 0, iso-C15 : 0 and C16 : 0, the polar lipid profile contained the major components diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified glycolipid, the major quinone was menaquinone MK-7 and the major compound in the polyamine pattern was spermidine. Additionally, DNA-DNA hybridization with B. drentensis LMG 21831T, B. vireti LMG 21834T and B. soli LMG 21838T resulted in relatedness values that were clearly below 70 %. Physiological and biochemical test results were also different from those of the most closely related species. As a consequence, AP-6T represents a novel species of the genus Bacillus, for which the name Bacillus cucumis sp. nov. is proposed, with AP-6T ( = CIP 110974T = CCM 8651T) as the type strain.

Paenibacillus cucumis sp. nov., isolated from a cucumber plant.

A Gram-positive-staining, aerobic, endospore-forming bacterial strain, isolated from the stem of a cucumber plant, was studied in detail for its taxonomic position. Based on 16S rRNA gene sequence similarity comparisons, strain AP-115T was grouped into the genus Paenibacillus, most closely related to Paenibacillus amylolyticus (98.8 %), Paenibacillus tundrae and Paenibacillus barcinonensis (both 98.4 %). The 16S rRNA gene sequence similarity to other species of the genus Paenibacillus was ≤98.4 %. Chemotaxonomic characterization supported allocation of the strain to the genus Paenibacillus. The quinone system contained exclusively menaquinone MK-7, and in the polar lipid profile diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylserine were predominating. The major component in the polyamine pattern was spermidine, and the diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid. The major fatty acids were iso- and anteiso-branched fatty acids. The results of physiological and biochemical tests allowed phenotypic differentiation of strain AP-115T from closely related species. Thus, AP-115T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus cucumis sp. nov. is proposed, with AP-115T (=LMG 29222T=CCM 8653T) as the type strain.

Isoptericola cucumis sp. nov., isolated from the root tissue of cucumber (Cucumis sativus).

A Gram-stain-positive, aerobic organism, showing an irregular cell morphology, was isolated from the root tissue of cucumber (Cucumis sativus) and investigated in detail for its taxonomic position. On the basis of the 16S rRNA gene sequence analysis, strain AP-38T was shown to be most closely related to Isoptericola variabilis (99.1 %) and Isoptericola nanjingensis (98.9 %). The 16S rRNA gene sequence similarity to all other species of the genus Isoptericola was ≤98.5 %. DNA-DNA relatedness to Isoptericola variablis DSM 10177T and Isoptericola nanjingensis DSM 24300T was 31(reciprocal 41 %) and 34 (reciprocal 34 %), respectively. The diagnostic diamino acid of the peptidoglycan was l-lysine. The quinone system contained predominantly menaquinones MK-9(H4) and MK-9(H2). In the polar lipid profile, major compounds were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two phosphatidylinositol mannosides. The polyamine pattern contained the major components spermidine and spermine and significant amounts of tyramine. In the fatty acid profile, anteiso-C15 : 0 and iso-C15 : 0 were present in major amounts. These data support the allocation of the strain to the genus Isoptericola. The results of physiological and biochemical characterization additionally provide phenotypic differentiation of strain AP-38T from I. variabilis and I. nanjingensis. AP-38T represents a novel species of the genus Isoptericola, for which we propose the name Isoptericola cucumis sp. nov., with AP-38T (= LMG 29223T=CCM 8653T) as the type strain.

The influence of microbial-based inoculants on N2O emissions from soil planted with corn (Zea mays L.) under greenhouse conditions with different nitrogen fertilizer regimens.

Nitrous oxide (N2O) emissions are increasing at an unprecedented rate owing to the increased use of nitrogen (N) fertilizers. Thus, new innovative management tools are needed to reduce emissions. One potential approach is the use of microbial inoculants in agricultural production. In a previous incubation study, we observed reductions in N2O emissions when microbial-based inoculants were added to soil (no plants present) with N fertilizers under laboratory incubations. This present study evaluated the effects of microbial-based inoculants on N2O and carbon dioxide (CO2) emissions when applied to soil planted with corn (Zea mays L.) under controlled greenhouse conditions. Inoculant treatments consisted of (i) SoilBuilder (SB), (ii) a metabolite extract of SoilBuilder (SBF), and (iii) a mixture of 4 strains of plant-growth-promoting Bacillus spp. (BM). Experiments included an unfertilized control and 3 N fertilizers: urea, urea - ammonium nitrate with 32% N (UAN-32), and calcium - ammonium nitrate with 17% N (CAN-17). Cumulative N2O fluxes from pots 41 days after planting showed significant reductions in N2O of 15% (SB), 41% (BM), and 28% (SBF) with CAN-17 fertilizer. When UAN-32 was used, reductions of 34% (SB), 35% (SBF), and 49% (BM) were obtained. However, no reductions in N2O emissions occurred with urea. Microbial-based inoculants did not affect total CO2 emissions from any of the fertilized treatments or the unfertilized control. N uptake was increased by an average of 56% with microbial inoculants compared with the control (nonmicrobial-based treatments). Significant increases in plant height, SPAD chlorophyll readings, and fresh and dry shoot mass were also observed when the microbial-based treatments were applied (with and without N). Overall, results demonstrate that microbial inoculants can reduce N2O emissions following fertilizer application depending on the N fertilizer type used and can enhance N uptake and plant growth. Future studies are planned to evaluate the effectiveness of these microbial inoculants in field-based trials and determine the mechanisms involved in N2O reduction.

Bacillusin A, an Antibacterial Macrodiolide from Bacillus amyloliquefaciens AP183.

Bioassay-guided fractionation of the organic extracts of a Bacillus amyloliquefaciens strain (AP183) led to the discovery of a new macrocyclic polyene antibiotic, bacillusin A (1). Its structure was assigned by interpretation of NMR and MS spectroscopic data as a novel macrodiolide composed of dimeric 4-hydroxy-2-methoxy-6-alkenylbenzoic acid lactones with conjugated pentaene-hexahydroxy polyketide chains. Compound 1 showed potent antibacterial activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium with minimum inhibitory concentrations in a range of 0.6 to 1.2 µg/mL. The biosynthetic significance of this unique class of antibiotic compounds is briefly discussed.

Microbial-based inoculants impact nitrous oxide emissions from an incubated soil medium containing urea fertilizers.

There is currently much interest in developing crop management practices that will decrease NO emissions from agricultural soils. Many different approaches are being investigated, but to date, no studies have been published on how microbial inoculants affect NO emissions. This study was conducted to test the hypothesis that microbial-based inoculants known to promote root growth and nutrient uptake can reduce NO emissions in the presence of N fertilizers under controlled conditions. Carbon dioxide and CH fluxes were also measured to evaluate microbial respiration and determine the aerobic and anaerobic conditions of the incubated soil. The microbial-based treatments investigated were SoilBuilder (SB), a metabolite extract of SoilBuilder (SBF), and a mixture of four strains of plant growth-promoting spp. Experiments included two different N fertilizer treatments, urea and urea-NHNO 32% N (UAN), and an unfertilized control. Emissions of NO and CO were determined from soil incubations and analyzed with gas chromatography. After 29 d of incubation, cumulative NO emissions were reduced 80% by SB and 44% by SBF in soils fertilized with UAN. Treatment with spp. significantly reduced NO production on Days 1 and 2 of the incubation in soils fertilized with UAN. In the unfertilized treatment, cumulative emissions of NO were significantly reduced 92% by SBF. Microbial-based treatments did not reduce NO emissions associated with urea application. Microbial-based treatments increased CO emissions from soils fertilized with UAN, suggesting a possible increase in microbial activity. Overall, the results demonstrated that microbial-based inoculants can reduce NO emissions associated with N fertilizer application, and this response varies with the type of microbial-based inoculant and fertilizer.

Biocontrol of the Reniform Nematode by Bacillus firmus GB-126 and Paecilomyces lilacinus 251 on Cotton.

Due to increased restrictions on the use of chemical nematicides, alternative nematode management strategies, including biocontrol, are needed. The objectives of this study were to evaluate the potential of Bacillus firmus GB-126 and Paecilomyces lilacinus 251 in commercial formulations applied separately or concomitantly to manage Rotylenchulus reniformis in cotton grown under greenhouse, microplot, and field conditions. In the greenhouse, seed treated with B. firmus (1.4 × 107 CFU/seed), an application of P. lilacinus (0.3% vol/vol of water), or the combination of B. firmus and P. lilacinus reduced the number of females, eggs, and vermiforms of R. reniformis (P ≤ 0.02) and increased populations of free-living nematodes (P ≤ 0.01). In microplots and field conditions, populations of R. reniformis vermiforms decreased when exposed to B. firmus and P. lilacinus biocontrol agents at midseason (P ≤ 0.04). Furthermore, stem diameter and free-living nematode numbers increased (P ≤ 0.01) with the combination of B. firmus and P. lilacinus. In the field, numbers of females, eggs, and vermiform life stages at the end of the growing season decreased in the presence of the biocontrol agents applied individually or concomitantly (P ≤ 0.01). Cotton yields from the application of B. firmus GB-126 and P. lilacinus 251 were similar to those from aldicarb, the chemical nematicide standard.