Enhancing systematic tolerance in Bermuda grass (Cynodon dactylon L.) through amplified alkB gene expression and bacterial-driven hydrocarbon degradation.

This study aimed to access the impact of soil polluted with petroleum (5, 10 g petroleum kg-1 soil) on Bermuda grass (Cynodon dactylon L.) with and without applied bacterial inoculants (Arthrobacter oxydans ITRH49 and Pseudomonas sp. MixRI75). Both soil and seed were given bacterial inoculation. The evaluated morphological parameters of Bermuda grass were fresh and dry weight. The results demonstrated that applied bacterial inoculants enhanced 5.4%, 20%, 28% and 6.4%, 21%, and 29% shoot and root fresh/dry weights in Bermuda grass under controlled environment. The biochemical analysis of shoot and root was affected deleteriously by the 10 g petroleum kg-1 soil pollution. Microbial inoculants enhanced the activities of enzymatic (catalase, peroxidase, glutathione reductase, ascorbate peroxidase, superoxide dismutase) and non-enzymatic (ɑ-tocopherols, proline, reduced glutathione, ascorbic acid) antioxidant to mitigate the toxic effects of ROS (H2O2) under hydrocarbon stressed condition. The maximum hydrocarbon degradation (75%) was recorded by Bermuda grass at 5 g petroleum kg-1 soil contamination. Moreover, bacterial persistence and alkane hydroxylase gene (alkB) abundance and expression were observed more in the root interior than in the rhizosphere and shoot interior of Bermuda grass. Subsequently, the microbe used a biological tool to propose that the application of plant growth-promoting bacteria would be the most favorable choice in petroleum hydrocarbon polluted soil to conquer the abiotic stress in plants and the effective removal of polyaromatic hydrocarbons in polluted soil.

Incorporating microbial inoculants to reduce nitrogen loss during sludge composting by suppressing denitrification and promoting ammonia assimilation.

To address the challenge of increasing nitrogen retention in compost, this study investigated the effects of microbial communities on denitrification and ammonia assimilation during sludge composting by inoculating microbial inoculants. The results showed that the retention rates of total Kjeldahl nitrogen (TKN) and humic acid (HA) in MIs group (with microbial inoculants) were 4.94 % and 18.52 % higher than those in the control group (CK), respectively. Metagenomic analysis showed that Actinobacteria and Proteobacteria were identified as main microorganisms contributing to denitrification and ammonia assimilation. The addition of microbial agents altered the structure of the microbial community, which in turn stimulated the expression of functional genes. During cooling period, the ammonia assimilation genes glnA, gltB and gltD in MIs were 15.98 %, 24.84 % and 32.88 % higher than those in CK, respectively. Canonical correspondence analysis revealed a positive correlation between the dominant bacterial genera from the cooling stage to the maturity stage and the levels of NO3--N, NH4+-N, HA, and TKN contents. NH4+-N was positively correlated with HA, indicating NH4+-N might be incorporated into HA. Heat map and network analyses revealed NH4+-N as a key factor affecting functional genes of denitrification and ammonia assimilation, with Nitrospira identified as the core bacteria in the microbial network. Therefore, the addition of microbial agents could increase nitrogen retention and improve compost product quality.

Autumn grass treated with a hydrolysable tannin extract versus lactic acid bacteria inoculant: Effects on silage fermentation characteristics and nutritional value and on performance of lactating dairy cows.

Hydrolysable tannins (HT) show potential as silage additive for autumn herbage silages, high in (rumen degradable) protein, as they may reduce proteolysis. Additionally, they have abilities to form pH-reversible tannin-protein complexes, non-degradable in the rumen but degradable in the abomasum and intestines of ruminants. Therefore they can improve milk N efficiency and shift N excretions from urine to faeces, possibly mitigating the environmental impact of ruminants. In this study, two small bunker silos were filled with autumn grass. One was treated with 20 g/kg DM HT extract (TAN) (TannoSan-L), the other with 8 mg/kg DM inoculant containing lactic acid bacteria (INO) (Bonsilage Fit G). Secondly, micro-silos (2.75 L) were filled with four treatments; (1) grass without additive (CON) (n = 5); (2) TAN (n = 5); (3) INO (n = 5); and (4) TAN + INO (n = 5). The bunker silos were used in a cross-over feeding experiment with periods of 4 weeks involving 22 lactating Holstein cows (average ± SD: 183 ± 36.3 days in milk, 665 ± 71.0 kg body weight, and 33.8 ± 3.91 kg/day milk yield). The HT dose was insufficient to reduce proteolysis or alter chemical composition and nutritional value in the micro- and bunker silages. Including grass silage added with TAN (3.2 g HT/kg DM) in the diet, did not affect feed intake nor fat and protein corrected milk yield in comparison to feeding the grass silage added with INO in a similar diet. The TAN-fed cows had an increased faecal N excretion and decreased apparent total-tract N and organic matter digestibility, but no improvement in the cows' N utilization could be confirmed in milk and blood urea levels. Overall, feeding an autumn grass silage treated with 20 g/kg chestnut HT extract did not affect the performance of dairy cows in comparison to feeding an autumn grass silage treated with a lactic acid bacteria inoculant.

Organic matter stabilization and phosphorus activation during vegetable waste composting: Multivariate and multiscale investigation.

The conversion of organic matter and P in the waste composting process affects the efficiency of the composted product. However, the addition of microbial inoculants may improve the conversion characteristics of organic matter and P. In this study, straw-decomposing microbial inoculant (SDMI) was added to investigate its effects on the organic matter stabilization and phosphorus activation during the composting of vegetable waste (VWs). Aliphatic carboxyl-containing compounds were degraded during composting, but the stability of the organic matter and P was improved. The addition of SDMI promoted the degradation of dissolved organic carbon by 81.7 % and improved P stability and thermal stability of organic matter. Hedley sequential P fractionation showed a decrease in the H2O-P proportion by >12 % and increased in the HCl-P proportion by >4 % by the end of composting. Stable forms of P, such as AlPO4 and iron-containing phosphate, were the main forms of P in the final compost. The results provide a basis for producing high-quality vegetable compost products and improving the reutilization potential of VWs.

Community Synergy of Lactic Acid Bacteria and Cleaner Fermentation of Oat Silage Prepared with a Multispecies Microbial Inoculant.

To investigate community synergy of lactic acid bacteria (LAB) and cleaner fermentation of oat silage, oat silages were prepared with or without (control) commercial LAB inoculants LI1 (containing Lactiplantibacillus plantarum, Lentilactobacillus buchneri, Lacticaseibacillus paracasei, and Pediococcus acidilactici) and LI2 (containing Lactiplantibacillus plantarum and Lentilactobacillus buchneri). The microbial community, LAB synergy, and cleaner fermentation were analyzed at 1, 3, 6, 15, 35, and 90 days of ensiling. The LAB inoculant improved fermentation quality, with significantly (P < 0.05) lower pH, ammonia nitrogen content, and gas production and higher lactic acid and acetic acid contents than those of the control. Enterobacteriaceae was the main bacterial community in early stage of fermentation, which utilizes sugar to produce CO2 gas, causing dry matter (DM) and energy loss. As fermentation progressed, the microbial diversity decreased, and the microbial community shifted from Gram-negative to Gram-positive bacteria. The inoculation of multispecies LAB displayed community synergy; Pediococcus acidilactici formed a dominant community in the early stage of fermentation, which produced an acid and anaerobic environment for the subsequent growth of Lentilactobacillus and Lacticaseibacillus species, thus forming a LAB-dominated microbial community. The predicted functional profile indicated that the silage inoculated with LI1 enhanced the carbohydrate metabolism pathway but inhibited the amino acid metabolism pathway, which played a role in promoting faster lactic acid production, reducing the decomposition of protein to ammonia nitrogen, and improving the fermentation quality of silage. Therefore, oat silage can be processed to high-quality and cleaner fermented feed by using an LAB inoculant, and LI1 showed better efficiency than LI2. IMPORTANCE Oat natural silage is rich in Enterobacteriaceae, increasing gas production and fermentation loss. Lactic acid bacteria interact synergistically to form a dominant community during ensiling. Pediococci grow vigorously in the early stage of fermentation and create an anaerobic environment. Lactobacilli inhibit the harmful microorganisms and result in cleaner fermentation of oat silage.

Mitigation of arsenic toxicity in rice by the co-inoculation of arsenate reducer yeast with multifunctional arsenite oxidizing bacteria.

The study aimed to explicate the role of microbial co-inoculants for the mitigation of arsenic (As) toxicity in rice. Arsenate (AsV) reducer yeast Debaryomyces hansenii NBRI-Sh2.11 (Sh2.11) with bacterial strains of different biotransformation potential was attempted to develop microbial co-inoculants. An experiment to test their efficacy (yeast and bacterial strains) on plant growth and As uptake was conducted under a stressed condition of 20 mg kg-1 of arsenite (AsIII). A combination of Sh2.11 with an As(III)-oxidizer, Citrobacter sp. NBRI-B5.12 (B5.12), resulted in ∼90% decrease in grain As content as compared to Sh2.11 alone (∼40%). Reduced As accumulation in rice roots under co-treated condition was validated with SEM-EDS analysis. Enhanced As expulsion in the selected combination under in vitro conditions was found to be correlated with higher As content in the soil during their interaction with plants. Selected co-inoculant mediated enhanced nutrient uptake in association with better production of indole acetic acid (IAA) and gibberellic acid (GA) in shoot, support microbial co-inoculant mediated better biomass under stressful condition. Boosted defense response in association with enhanced glutathione-S-transferase (GST) and glutathione reductase (GR), activities under in vitro and in vivo conditions were observed. These results indicated that the As(III) oxidizer-B5.12 accelerated the As detoxification property of the As(V) reducer-Sh2.11. Henceforth, the results confer that the coupled reduction-oxidation process of the co-inoculant reduces the accumulation of As in rice grain. These co-inoculants can be further developed for field trials to achieve higher biomass with alleviated As toxicity in rice.

Ensiling pretreatment fortified with laccase and microbial inoculants enhances biomass preservation and bioethanol production of alfalfa stems.

This study investigated the potential of ensiling pretreatment fortified with laccase and a lactic acid bacteria (LAB) inoculant on improving the utilization of alfalfa stems for bioethanol production. The alfalfa stems were ensiled with no additives (Con), 0.04 % laccase (LA), a LAB inoculant containing Pediococcus pentosaceus at 1 × 106 fresh weight (FW) and Pediococcus acidilactici at 3 × 105 cfu/g FW (PP), and a combination of LA and PP (LAP) for 120 days. By reshaping the bacterial community structure of alfalfa stem silages toward a higher abundance of Lactobacillus, the addition of laccase and LAB inoculant either alone or in combination facilitated lactic acid fermentation to reduce fermentation losses, as evidenced by low concentrations of ammonia nitrogen (53.7 to 68.9 g/kg total nitrogen) and ethanol (2.63 to 3.55 g/kg dry matter). All additive treatments increased lignocellulose degradation and soluble sugars concentrations of alfalfa stem silages. Due to delignification and polyphenol removal, glucan and xylan conversion (70.3 % vs. 35.7 % and 51.6 % vs. 27.9 %, respectively) and ethanol conversion efficiency (53.9 % vs. 26.4 %) of alfalfa stems were greatly increased by ensiling fortified with LA versus Con, and these variables (79.8 % for glucan, 58.7 % for xylan, and 60.1 % for ethanol conversion efficiency) were further enhanced with a synergistic effect of LA and PP fortification. The spearman correlation analysis revealed that bioethanol fermentation of silage biomass was closely related to ensiling parameters and total phenols. In conclusion, ensiling pretreatment with LA and PP combination offered a feasible way to efficient utilization of alfalfa stems for bioethanol production.

Exploring the PAHs dissipation and indigenous bacteria response in soil amended with two different microbial inoculants.

This study investigated the bioremediation of PAHs in soil by two different microbial inoculants prepared with Paracoccus aminovorans HPD-2 and the carrier humic acid (HA) or montmorillonite (Mont). After incubation for 42 d, the greatest removal of PAHs, 42.8 % or 41.6 %, was observed in microcosms with 0.2 % HA inoculant or 2 % Mont inoculant. The PAH removal efficiency in these treatments was significantly greater than that in soil amended only with planktonic HPD-2. Bacterial community analysis showed that the survival of Paracoccus aminovorans was enhanced in the treatments with Mont inoculant compared with the treatments with HA inoculant or with HPD-2 alone. Moreover, the diversity of PAH-degrading bacterial genera was greater in the treatments containing Mont inoculant than in the treatments containing HA inoculant. These results indicate that the organic material HA and inorganic material Mont promote PAH removal in different ways. Specifically, HA promotes PAHs bioavailability to accelerate the degradation of PAHs in soil, whereas Mont protects PAH-degrading microorganisms to promote pollutant removal. Overall, the findings suggest that HA and Mont are promising materials for microbial immobilization for the bioremediation of PAH-contaminated soil.

Changes in Composition and Diversity of Epiphytic Microorganisms on Field Pea Seeds, Partial Crop Peas, and Whole Crop Peas during Maturation and Ensiling with or without Lactic Acid Bacteria Inoculant.

The present study was conducted under the hypothesis that, in field peas, type of plant material, stage of maturity, ensiling, silage additive, and aerobic stress affect the composition and diversity of epiphytic microbial communities. Epiphytic microbial composition and diversity of pea seeds, partial crop peas, and whole crop peas was analyzed at different stages of late maturity, before and after ensiling, and with or without the use of lactic acid bacteria (LAB) as inoculant. Suitable combinations among pea crop variants, maturity stages, and inoculant use for the production of stable silages with sufficient aerobic stability after opening and during feed-out were identified. Genomic DNA was extracted, and 16S and 18S rRNA gene amplicons were sequenced. To assess the quality of the various silages, nutrient concentration, pH value, concentration of lactic acid, short chain fatty acids, and alcohols, and aerobic stability were determined. Pea seeds were barely colonized by epiphytic microorganisms. In partial and whole crop peas, composition and α-diversity (Shannon index) of bacterial communities did not differ between crop variants but differed among maturity stages. Epiphytic eukaryotes were rarely found on partial and whole crop peas. Bacterial composition and α-diversity were affected by ensiling and subsequent aerobic storage. In partial and whole crop peas, plant maturation caused an increase of the relative abundance of naturally occurring LAB (Weissella, Pediococcus, and Lactobacillus spp.). As a possible result, natural LAB support stable ensiling conditions even without the use of inoculants beginning with a maturity of 78 on the BBCH scale. This corresponded with a dry matter (DM) concentration of 341 and 363 g/kg in partial and whole crop peas, respectively. Addition of LAB inoculants, however, reduced ammonia, acetic acid, and butanol concentrations, and supported aerobic stability. Earlier stages of plant maturity (BBCH 76 and 77, 300 g DM/kg or less) were more prone to microbial spoilage. Stable pea seed silages can be produced at a maturity between BBCH 78 (427 g DM/kg) and 79 (549 g DM/kg), but they undoubtedly require LAB inoculation or application of other ensiling agents. IMPORTANCE Field peas are important protein suppliers for human and animal nutrition. They can be grown in many areas of the world, which may reduce imports of protein plants and has beneficial economic and ecological effects. Ensiling is a method of preserving feed that can be implemented easily and cost-effectively at the farm. Peas harvested as seeds, partial crop, or whole crop at different maturities enable a wide range of applications. The study characterized epiphytic microbial communities on peas in terms of composition and diversity depending on the maturity of the plants and feed conservation by ensiling as they play an essential role for the production of silages. Even if this study did not consider year, site, or cultivar effects, the results would show which part of the plant is probably well suited for the production of stable and high-quality silages and at which stage of maturity.

Bacterial inoculant-assisted phytoremediation affects trace element uptake and metabolite content in Salix atrocinerea.

Natural plant-associated microorganisms are of critical importance to plant growth and survival in field conditions under toxic concentrations of trace elements (TE) and these plant-microbial processes can be harnessed to enhance phytoremediation. The total bacterial diversity from grey willow (Salix atrocinerea) on a brownfield heavily-polluted with lead (Pb) and arsenic (As) was studied through pyrosequencing. Culturable bacteria were isolated and in vitro tested for plant growth-promotion (PGP) traits, arsenic (As) tolerance and impact on As speciation. Two of the most promising bacterial strains - the root endophyte Pantoea sp. AV62 and the rhizospheric strain Rhodococcus erythropolis AV96 - were inoculated in field to S. atrocinerea. This bioaugmentation resulted in higher As and Pb concentrations in both, roots and leaves of bacterial-inoculated plants as compared to non-inoculated plants. In consequence, bacterial bioaugmentation also affected parameters related to plant growth, oxidative stress, the levels of phytochelatins and phenylpropanoids, together with the differential expression of genes related to these tolerance mechanisms to TE in leaves. This study extends our understanding about plant-bacterial interactions and provides a solid basis for further bioaugmentation studies aiming to improve TE phytoremediation efficiency and predictability in the field.

Local Network Properties of Soil and Rhizosphere Microbial Communities in Potato Plantations Treated with a Biological Product Are Important Predictors of Crop Yield.

Understanding the effectiveness and potential mechanism of action of agricultural biological products under different soil profiles and crops will allow more precise product recommendations based on local conditions and will ultimately result in increased crop yield. This study aimed to use bulk soil and rhizosphere microbial composition and structure to evaluate the potential effect of a Bacillus amyloliquefaciens inoculant (strain QST713) on potatoes and to explore its relationship with crop yield. We implemented next-generation sequencing (NGS) and bioinformatics approaches to assess the bacterial and fungal biodiversity in 185 soil samples, distributed over four different time points-from planting to harvest-from three different geographical locations in the United States. In addition to location and sampling time (which includes the difference between bulk soil and rhizosphere) as the main variables defining the microbiome composition, the microbial inoculant applied as a treatment also had a small but significant effect in fungal communities and a marginally significant effect in bacterial communities. However, treatment preserved the native communities without causing a detectable long-lasting effect on the alpha- and beta-diversity patterns after harvest. Using information about the application of the microbial inoculant and considering microbiome composition and structure data, we were able to train a Random Forest model to estimate if a bulk soil or rhizosphere sample came from a low- or high-yield block with relatively high accuracy (84.6%), concluding that the structure of fungal communities gives us more information as an estimator of potato yield than the structure of bacterial communities. IMPORTANCE Our results reinforce the notion that each cultivar on each location recruits a unique microbial community and that these communities are modulated by the vegetative growth stage of the plant. Moreover, inoculation of a Bacillus amyloliquefaciens strain QST713-based product on potatoes also changed the abundance of specific taxonomic groups and the structure of local networks in those locations where the product caused an increase in the yield. The data obtained, from in-field assays, allowed training a predictive model to estimate the yield of a certain block, identifying microbiome variables-especially those related to microbial community structure-even with a higher predictive power than the geographical location of the block (that is, the principal determinant of microbial beta-diversity). The methods described here can be replicated to fit new models in any other crop and to evaluate the effect of any agricultural input in the composition and structure of the soil microbiome.

Effect of Microbial Inoculation on Carbon Preservation during Goat Manure Aerobic Composting.

Carbon is the crucial source of energy during aerobic composting. There are few studies that explore carbon preservation by inoculation with microbial agents during goat manure composting. Hence, this study inoculated three proportions of microbial agents to investigate the preservation of carbon during goat manure composting. The microbial inoculums were composed of Bacillus subtilis, Bacillus licheniformis, Trichoderma viride, Aspergillus niger, and yeast, and the proportions were B1 treatment (1:1:1:1:2), B2 treatment (2:2:1:1:2), and B3 treatment (3:3:1:1:2). The results showed that the contents of total organic carbon were enriched by 12.21%, 4.87%, and 1.90% in B1 treatment, B2 treatment, and B3 treatment, respectively. The total organic carbon contents of B1 treatment, B2 treatment, and B3 treatment were 402.00 ± 2.65, 366.33 ± 1.53, and 378.33 ± 2.08 g/kg, respectively. B1 treatment significantly increased the content of total organic carbon compared with the other two treatments (p < 0.05). Moreover, the ratio of 1:1:1:1:2 significantly reduced the moisture content, pH value, EC value, hemicellulose, and lignin contents (p < 0.05), and significantly increased the GI value and the content of humic acid carbon (p < 0.05). Consequently, the preservation of carbon might be a result not only of the enrichment of the humic acid carbon and the decomposition of hemicellulose and lignin, but also the increased OTU amount and Lactobacillus abundance. This result provided a ratio of microbial agents to preserve the carbon during goat manure aerobic composting.

Effect of exopolysaccharides of Paenibacillus polymyxa rhizobacteria on physiological and morphological variables of wheat seedlings.

Paenibacillus polymyxa is a promising plant-growth-promoting rhizobacterium that associates with a wide range of host plants, including agronomically important ones. Inoculation of wheat seedlings with P. polymyxa strains CCM 1465 and 92 was found to increase the mitotic index of the root cells 1.2- and 1.6-fold, respectively. Treatment of seedlings with the exopolysaccharides (EPSs) of these strains increased the mitotic index 1.9-fold (P. polymyxa CCM 1465) and 2.8-fold (P. polymyxa 92). These increases indicate activation of cell division in the root meristems. Analysis of the morphometric variables of the seedlings showed that P. polymyxa CCM 1465, P. polymyxa 92, and their EPSs promoted wheat growth, increasing root and shoot length up to 22% and root and shoot dry weight up to 28%, as compared with the control. In addition, both strains were found to intensely colonize the seedling root surface. Thus, P. polymyxa EPSs are active metabolites that, along with whole cells, are responsible for the contact interactions of the bacteria with wheat roots and are implicated in the induction of plant responses to these interactions. The strains used in this work are of interest for further study to broaden the existing understanding of the mechanisms of plant-bacterial interactions and to develop effective biofertilizers for agricultural purposes.

Response of the microbial community to phosphate-solubilizing bacterial inoculants on Ulmus chenmoui Cheng in Eastern China.

Phosphate-solubilizing bacteria (PSB) have beneficial effects on plant health and soil composition. To date, studies of PSB in soil have largely been performed under field or greenhouse conditions. However, less is known about the impact of introducing indigenous PSB in the field, including their effects on the local microbial community. In this study, we conducted greenhouse and field experiments to explore the effects of the addition of indigenous PSB on the growth of Chenmou elm (Ulmus chenmoui) and on the diversity and composition of the bacterial community in the soil. We obtained four bacterial isolates with the highest phosphate-solubilizing activity: UC_1 (Pseudomonas sp.), UC_M (Klebsiella sp.), UC_J (Burkholderia sp.), and UC_3 (Chryseobacterium sp.). Sequencing on the Illumina MiSeq platform showed that the inoculated PSB did not become the dominant strains in the U. chenmoui rhizosphere. However, the soil bacterial community structure was altered by the addition of these PSB. The relative abundance of Chloroflexi decreased significantly in response to PSB application in all treatment groups, whereas the populations of several bacteria, including Proteobacteria and Bacteroidetes, increased. Network analysis indicated that Chloroflexi was the most strongly negatively correlated with Proteobacteria, whereas Proteobacteria was strongly positively correlated with Bacteroidetes. Our findings indicate that inoculation with PSB (UC_1, UC_M, UC_J, and UC_3) can improve the growth of U. chenmoui and regulate its rhizosphere microbial community. Therefore, inoculation with these bacterial strains could promote the efficient cultivation and production of high-quality plant materials.

Mobilization of recalcitrant phosphorous and enhancement of pepper P uptake and yield by a new biocontrol and bioremediation bacterium Burkholderia cepacia CQ18.

AIMS: Phosphorus (P) is a finite resource and inoculation of phosphorus-mobilizing bacteria (PMB) is a promising approach for the enhancement of soil P availability and plant P uptake. This drives scientists to search for the microbes effective in mobilizing legacy P in soils. METHODS AND RESULTS: The current incubation and greenhouse pot experiments were conducted to investigate P mobilization and pepper P uptake as affected by a new biocontrol and bioremediation bacterium Burkholderia cepacia CQ18. This bacterium converted Ca3 (PO4 )2 , FePO4 , AlPO4 , and lecithin into soluble inorganic P in the culture solutions and increased available P (including water-soluble P and Olsen P) in the soil. There were positive correlations between the soluble inorganic phosphorus and the exudates (protons, organic acids (oxalate and gluconate), siderophores and phosphatases) in culture solutions. Pepper plant biomass, fruit yield and P uptake changed in the sequence: chemical fertilizers plus bacterial inoculant >only chemical fertilizers >only bacterial inoculant >blank control. CONCLUSIONS: Taking into account the wide spectrums of P mobilization and simultaneous production of acid, neutral and alkaline phosphatases at a given pH, B.cepacia CQ18 may be a potential PMB used in soils with wide pH ranges. The mechanisms employed by this bacterium in the solubilization of recalcitrant inorganic P could be the efflux of protons, organic acids (oxalate and gluconate) and siderophores. Phosphatases could be of utmost importance in the mineralization of the organic P. The production of siderophores and phosphatases by of B.cepacia CQ18 could thus be crucial for not only the antagonism against plant pathogens but also the mobilization of soil sparingly available P. SIGNIFICANCE AND IMPACT OF THE STUDY: Burkholderia cepacia CQ18 could be potentially developed into a biofertilizer.

Novel sulphur-oxidizing bacteria consummate sulphur deficiency in oil seed crop.

Plants absorb sulphate, the oxidized form of elemental sulphur (S°), from soil. Sulphur-oxidizing bacteria play a key role in transformation of sulphur in soil. Oil seed crops require high amount of sulphur and it plays an important role in the formation of proteins, vitamins and enzymes. It increases yield, oil content and protein content in oil seed crops. Sulphur is the important constituent of amino acids, viz. methionine, cystine, and cysteine. It necessitates various enzymatic, metabolic processes such as photosynthesis and nitrogen fixation. In the last few years, the prominence of sulphur in oil seed crop nutrition has been accepted as widespread occurrence of its inadequacy in agricultural soil. Approximately 41% of Indian soil is deficient in sulphur. The soil microbial population is the major enforcement behind sulphur transformation. They mineralize, immobilize, oxidize and reduce the elemental and other reduced forms of sulphur. The main step in transformation is oxidation carried out by microorganisms to convert sulphur into sulphate. The chemolithotrophic bacteria belonging to genus Thiobacillus are of primary importance; there are heterotrophic bacteria also which can oxidize sulphur in soil. The pH reduction at the time of oxidation helps in mineralization and absorption of other essential nutrients also. This property of sulphur-oxidizing bacteria (SOB) shows their potential to be used as bioinoculants. Bioformulations prepared using carrier-based formulations, immobilization, biostimulation, etc., are sustainable forms of fertilizers. These SOB inoculants can be used to increase the fertility and sulphate production in soil.

Trichoderma strains accelerate maturation and increase available phosphorus during vermicomposting enriched with rock phosphate.

AIMS: To suggest microbial inoculation as a tool to shorten organic residues stabilization and increase rock phosphate (RP) solubilization through vermicomposting, thus increasing nutrient content in plants and making it more appealing to farmers. Two Trichoderma strains were inoculated alone or combined in a RP apatite-enriched vermicompost. Stability and plant-available phosphorus levels were monitored for 120 days. METHODS AND RESULTS: Observable higher total organic carbon reduction in the treatment with the combined Trichoderma strains, followed by the inoculation with T. asperellum and T. virens. Combined Trichoderma and inoculation with T. virens increased humic acids (HA) content in 38·2 and 25·0%, respectively; non-inoculated vermicompost with T. asperellum increased it by 15·0%. The combined Trichoderma strains and T. virens achieved the stability index based on the humic/fulvic acids (HA/FA) ratio after 120 days. T. asperellum, combined Trichoderma and T. virens increased the citric acid soluble-P content in 83·2, 62·2 and 49·5%, respectively, compared to the non-inoculated vermicompost. CONCLUSIONS: Inoculation with combined T. asperellum and T. virens efficiently accelerated vermicompost stabilization; T. asperellum increased the citric acid soluble-P in the final product. SIGNIFICANCE AND IMPACT OF THE STUDY: Combined Trichoderma inoculation and RP enrichment improves the vermicompost quality, increasing HA and citric acid soluble-P, recycling organic waste nutrients and reducing agricultural dependence on phosphate fertilizers.

Integrated use of phosphate-solubilizing Bacillus subtilis strain IA6 and zinc-solubilizing Bacillus sp. strain IA16: a promising approach for improving cotton growth.

Mineral nutrition of crop plants is one of the major challenges faced by modern agriculture, particularly in arid and semi-arid regions. In alkaline calcareous soils, the availability of phosphorus and zinc is critically less due to their fixation and precipitation as complexes. Farmers use fertilizers to fulfill crop requirements, but their efficacy is less, which increases production costs. Plant growth-promoting rhizobacteria (PGPR) can improve the availability of crop nutrients through solubilizing the insoluble compounds of phosphorus and zinc in soil. In the present study, a total of 40 rhizobacterial isolates were isolated from cotton rhizosphere and screened for improving cotton growth through the solubilization of phosphorus and zinc. Out of these 40 isolates, seven isolates (IA2, IA3, IA6, IA7, IA8, IA13, and IA14) efficiently solubilized insoluble rock phosphate while seven isolates (IA10, IA16, IA20, IA23, IA24, IA28, and IA30) were more efficient in solubilizing insoluble zinc oxide. In liquid media, strain IA7 (2.75 µg/mL) solubilized the highest amount of phosphate while the highest concentration of soluble zinc was observed in the broth inoculated with strain IA20 (3.94 µg/mL). Seven phosphate-solubilizing and seven zinc-solubilizing strains were evaluated using jar trial to improve the growth of cotton seedlings, and the results were quite promising. All the inoculated treatments showed improvement in growth parameters in comparison with control. Best results were shown by the combined application of IA6 and IA16, followed by the combination of strains IA7 and IA20. Based on the jar trial, the selected isolates were further characterized by plant growth-promoting characters such as siderophores production, HCN production, ammonia production, and exopolysaccharides production. These strains were identified through 16S rRNA sequencing as Bacillus subtilis IA6 (accession # MN005922), Paenibacillus polymyxa IA7 (accession # MN005923), Bacillus sp. IA16 (accession # MN005924), and Bacillus aryabhattai IA20 (accession # MN005925). It is hence concluded that the integrated use of phosphate-solubilizing and zinc-solubilizing strains as potential inoculants can be a promising approach for improving cotton growth under semi-arid conditions.

Bioaugmentation: possible scenarios due to application of bacterial preparations for remediation of oil-contaminated soil.

Although bioaugmentation is known as effective and environmentally friendly method increasing removal of hydrocarbons from oil-contaminated soil, it sometimes fails in soil restoration and disturbs the ecological state of soil. We studied possible scenarios of the introduction of oil-degrading bacteria into oil-contaminated podzolic soil assessing the environmental safety of different bacterial preparations in a long-term field experiment. Integral indicators characterizing the state of biocenosis included biological activity of soil and aboveground biomass of grasses. It has been established that bacterial preparations can have both positive and negative effects on the ecological state of soil and oil biodegradation. Of the five bacterial preparations studied, one had a pronounced positive effect on soil biological activity and oil mineralization processes. Two preparations did not accelerate oil biodegradation and were characterized by a weaker positive effect or even a lack of influence. Two more bacterial preparations had a significant negative impact on soil biological properties. These preparations slowed oil mineralization in soil. Both positive and negative effects of bacterial preparations were observed only during the first two years after their application. All preparations were not effective during the latter stages of long-term remediation processes. The results indicate that successful application of bioaugmentation for the restoration of oil-contaminated soil requires testing of environmental safety of bacterial preparations in a long-term field experiments prior to any treatment processes.

Improvement of the yield-related response of mycorrhized Lallemantia iberica to salinity through sulfur-oxidizing bacteria.

BACKGROUND: To investigate the effects of salinity as a serious environmental limiter of productivity on the yield-related traits of Lallemantia iberica, a split-plot experiment was performed for 2 years (2017-2018) based on a randomized complete block design with three replications at Urmia University (37°33'09″N, 45°05'53″E). The main plots included salinity stress at two levels (6.72 dS m-1 , and 0.91 dS m-1 as control), and subplots were inoculants at four levels (Funneliformis mosseae, Thiobacillus sp., F. mosseae + Thiobacillus sp., and no inoculation). RESULTS: In the saline condition, serious reductions in yield and yield components (numbers of capsules per plant, seeds per capsule, and seeds per plant, 1000-seed weight, seed and biological yields), concentrations of leaf phosphorus and potassium, and relative mycorrhizal dependency were observed, but against the harvest index the leaf sulfur and sodium contents were increased. Moreover, all morphological traits (plant height, number of branches and leaves, leaf weight, stem weight, and ratio of leaf weight to stem weight) were decreased under salinity conditions. Mycorrhizal inoculation enhanced the salinity-induced reduction of yield and morphological traits to some extent. Inoculation with Thiobacillus had superiority in some of the yield and morphological characteristics compared with those in the non-inoculated plants. CONCLUSION: Salinity stress can significantly affect the yield, morphological characteristics, nutrients content, and mycorrhizal dependency of L. iberica plants. This study exhibited the significant effects of single and simultaneous applications of F. mosseae and Thiobacillus on plant growth and yield in saline soils. © 2020 Society of Chemical Industry.