Co-inoculation Effect of Rhizobia and Plant Growth Promoting Rhizobacteria on Common Bean Growth in a Low Phosphorus Soil

Nitrogen (N) fixation through legume-Rhizobium symbiosis is important for enhancing agricultural productivity and is therefore of great economic interest. Growing evidence indicates that other soil beneficial bacteria can positively affect symbiotic performance of rhizobia. Nodule endophytic plant growth promoting rhizobacteria (PGPR) were isolated from common bean nodules from Nakuru County in Kenya and characterized 16S rDNA partial gene sequencing. The effect of co-inoculation of rhizobium and PGPR, on nodulation and growth of common bean (Phaseolus vulgaris L.) was also investigated using a low phosphorous soil under greenhouse conditions. Gram-positive nodule endophytic PGPR belonging to the genus Bacillus were successfully isolated and characterized. Two PGPR strains (Paenibacillus polymyxa and Bacillus megaterium), two rhizobia strains (IITA-PAU 987 and IITA-PAU 983) and one reference rhizobia strain (CIAT 899) were used in the co-inoculation study. Two common bean varieties were inoculated with Rhizobium strains singly or in a combination with PGPR to evaluate the effect on nodulation and growth parameters. Co-inoculation of IITA-PAU 987 + B. megaterium recorded the highest nodule weight (405.2 mg) compared to IITA-PAU 987 alone (324.8 mg), while CIAT 899 + B. megaterium (401.2 mg) compared to CIAT 899 alone (337.2 mg). CIAT 899 + B. megaterium recorded a significantly higher shoot dry weight (7.23 g) compared to CIAT 899 alone (5.80 g). However, there was no significant difference between CIAT 899 + P. polymyxa and CIAT 899 alone. Combination of IITA-PAU 987 and B. megaterium led to significantly higher shoot dry weight (6.84 g) compared to IITA-PAU 987 alone (5.32 g) but no significant difference was observed when co-inoculated with P. polymyxa. IITA-PAU 983 in combination with P. polymyxa led to significantly higher shoot dry weight (7.15 g) compared to IITA-PAU 983 alone (5.14 g). Plants inoculated with IITA-PAU 987 and B. megaterium received 24.0 % of their nitrogen demand from atmosphere, which showed a 31.1% increase compared to rhizobium alone. Contrast analysis confirmed the difference between the co-inoculation of rhizobia strains and PGPR compared to single rhizobia inoculation on the root dry weight. These results show that co-inoculation of PGPR and Rhizobia has a synergistic effect on bean growth. Use of PGPR may improve effectiveness of Rhizobium biofertilizers for common bean production. Testing of PGPR under field conditions will further elucidate their effectiveness on grain yields of common bean.

The Oenological Potential of Hanseniaspora uvarum in Simultaneous and Sequential Co-fermentation with Saccharomyces cerevisiae for Industrial Wine Production

In oenology, the utilization of mixed starter cultures composed by Saccharomyces and non-Saccharomyces yeasts is an approach of growing importance for winemakers in order to enhance sensory quality and complexity of the final product without compromising the general quality and safety of the oenological products. In fact, several non-Saccharomyces yeasts are already commercialized as oenological starter cultures to be used in combination with Saccharomyces cerevisiae, while several others are the subject of various studies to evaluate their application. Our aim, in this study was to assess, for the first time, the oenological potential of H. uvarum in mixed cultures (co-inoculation) and sequential inoculation with S. cerevisiae for industrial wine production. Three previously characterized H. uvarum strains were separately used as multi-starter together with an autochthonous S. cerevisiae starter culture in lab-scale micro-vinification trials. On the basis of microbial development, fermentation kinetics and secondary compounds formation, the strain H. uvarum ITEM8795 was further selected and it was co- and sequentially inoculated, jointly with the S. cerevisiae starter, in a pilot scale wine production. The fermentation course and the quality of final product indicated that the co-inoculation was the better performing modality of inoculum. The above results were finally validated by performing an industrial scale vinification The mixed starter was able to successfully dominate the different stages of the fermentation process and the H. uvarum strain ITEM8795 contributed to increasing the wine organoleptic quality and to simultaneously reduce the volatile acidity. At the best of our knowledge, the present report is the first study regarding the utilization of a selected H. uvarum strain in multi-starter inoculation with S. cerevisiae for the industrial production of a wine. In addition, we demonstrated, at an industrial scale, the importance of non-Saccharomyces in the design of tailored starter cultures for typical wines.

Co-inoculation of Bacillus sp. and Pseudomonas putida at different development stages acts as a biostimulant to promote growth, yield and nutrient uptake of tomato

AIMS

This study builds upon the premise that roots culture distinct bacteria at specific stages of plant growth to benefit of specific microbial services needed at that particular growth stage. Accordingly, we hypothesized that the co-inoculation of beneficial microbes with distinct properties at specific stages of plant development would enhance plant performance.

METHODS AND RESULTS

The chosen microbes were Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus mojavensis and Pseudomonas putida. These microbes were selected based on their specific services ranging from nutrient solubilization, root growth promotion and disease resistance, and were applied to the roots of tomato plants at specific time points when those services were needed the most by the plant. Laboratory and greenhouse studies were conducted to evaluate the effects of co-inoculation at specific stages of development compared to single microbial applications.

CONCLUSION

In general, the combination of three microbes gave the highest biomass and yield without the presence of disease. Applications of three microbes showed the highest root/shoot ratio, and applications of four microbes the lowest ratio. Pseudomonas putida significantly increased fruit macronutrient and micronutrient contents.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our studies suggest that co-inoculation of three or four microbes is a good strategy for healthy crop production.

Root colonization dynamics of two ectomycorrhizal fungi of contrasting life history strategies are mediated by addition of organic nutrient patches

•  Here we investigated whether root colonization dynamics of ectomycorrhizal fungi (EMF) of contrasting life history strategies (i.e. early vs late successional dominants) were affected by resource availability, as mediated either directly via the soil, or indirectly via host nutrition. •  In a two phase experiment, Pinus muricata seedlings were co-inoculated with spores of early (Rhizopogon occidentalis) and late (Tomentella sublilacina) successional dominant EMF, with or without squirrel faecal pellets added as a nutrient source, in single chambers (Phase A) subsequently converted to split-root chambers (Phase B). •  R. occidentalis colonized seedlings earlier than T. sublilacina. R. occidentalis root tip numbers peaked then declined in both treatments, but earlier in the minus pellet treatment than the plus. T. sublilacina increased steadily regardless of treatment. In the split-root treatment, we found no response by R. occidentalis, and a complex response by T. sublilacina, suggesting that plant nutrition may affect colonization dynamics. •  The strategy of R. occidentalis may be to colonize roots early in high resource environments; whereas that of T. sublilacina may be based upon slower colonization rates and greater competitive ability. The effect of nutrient additions on R. occidentalis may be highly dependent upon their timing.

Simultaneous and successive inoculations of yeasts and lactic acid bacteria on the fermentation of an unsulfited Tannat grape must

Interactions between yeasts and lactic acid bacteria are strain specific, and their outcome is expected to change in simultaneous alcoholic--malolactic fermentations from the pattern observed in successive fermentations. One Oenococcus oeni strain Lalvin VP41™ was inoculated with two Saccharomyces cerevisiae strains either simultaneously, three days after the yeast inoculation, or when alcoholic fermentation was close to finish. Early bacterial inoculations with each yeast strain allowed for the growth of the bacterial populations, and the length of malolactic fermentation was reduced to six days. Alcoholic fermentation by Lalvin ICV D80® yeast strain left the highest residual sugar, suggesting a negative effect of the bacterial growth and malolactic activity on its performance. In sequential inoculations the bacterial populations did not show actual growth with either yeast strain. In this strategy, both yeast strains finished the alcoholic fermentations, and malolactic fermentations took longer to finish. Lalvin ICV D80® allowed for higher viability and activity of the bacterial strain than Fermicru UY4® under the three inoculation strategies. This was beneficial for the sequential completion of both fermentations, but negatively affected the completion of alcoholic fermentation by Lalvin ICV D80® in the early bacteria additions. Conversely, Fermicru UY4®, which was rather inhibitory towards the bacteria, favored the timely completion of both fermentations simultaneously. As bacteria in early inoculations with low or no SO2 addition can be expected to multiply and interact with fermenting yeasts, not only are the yeast-bacterium strains combination and time point of the inoculation to be considered, but also the amount of bacteria inoculated.

Colonization and plant growth promoting characterization of endophytic Pseudomonas chlororaphis strain Zong1 isolated from Sophora alopecuroides root nodules

The endophytic strain Zong1 isolated from root nodules of the legume Sophora alopecuroides was characterized by conducting physiological and biochemical tests employing gfp-marking, observing their plant growth promoting characteristics (PGPC) and detecting plant growth parameters of inoculation assays under greenhouse conditions. Results showed that strain Zong1 had an effective growth at 28 ºC after placed at 4–60 ºC for 15 min, had a wide range pH tolerance of 6.0–11.0 and salt tolerance up to 5% of NaCl. Zong1 was resistant to the following antibiotics (μg/mL): Phosphonomycin (100), Penicillin (100) and Ampicillin (100). It could grow in the medium supplemented with 1.2 mmol/L Cu, 0.1% (w/v) methylene blue and 0.1–0.2% (w/v) methyl red, respectively. Zong1 is closely related to Pseudomonas chlororaphis based on analysis the sequence of 16S rRNA gene. Its expression of the gfp gene indicated that strain Zong1 may colonize in root or root nodules and verified by microscopic observation. Furthermore, co-inoculation with Zong1 and SQ1 (Mesorhizobium sp.) showed significant effects compared to single inoculation for the following PGPC parameters: siderophore production, phosphate solubilization, organic acid production, IAA production and antifungal activity in vitro. These results suggest strains P. chlororaphi Zong1 and Mesorhizobium sp. SQ1 have better synergistic or addictive effect. It was noteworthy that each growth index of co-inoculated Zong1+SQ1 in growth assays under greenhouse conditions is higher than those of single inoculation, and showed a significant difference (p < 0.05) when compared to a negative control. Therefore, as an endophyte P. chlororaphis Zong1 may play important roles as a potential plant-growth promoting agent.

Characterization of Verticillium dahliae and V. tricorpus Isolates from Lettuce and Artichoke

Verticillium isolates collected from lettuce and artichoke were characterized for morphology, growth and pathogenicity. Several isolates were identified as Verticillium tricorpus based on morphological and cultural characteristics, including the production of dark resting mycelia, chlamydospores, microsclerotia, and yellow to orange pigmentation in culture. Compared with isolates of V. dahliae, these isolates also produced microsclerotia and conidia that were significantly larger and exhibited a distinct growth pattern at varying temperatures. Using database sequence information, primers were developed from the internal transcribed spacer region to produce a diagnostic 337-bp product specific to V. tricorpus and used to confirm the identification of isolates. Pathogenicity tests indicated that isolates of V. tricorpus were weak pathogens, causing a median disease severity (DS) of <1 (0-to-5 scale) on lettuce and artichoke. In contrast, isolates of V. dahliae consistently caused severe wilt with a median DS of >3.5 on lettuce and 5.0 on artichoke. Although lettuce and artichoke inoculated with isolates of V. tricorpus exhibited reduced height and fresh foliar and root weight, the reductions were not statistically significant, unlike in plants inoculated with isolates of V. dahliae. Lettuce co-inoculated with isolates of V. tricorpus and V. dahliae exhibited reduced symptoms of Verticillium wilt and improved growth relative to those inoculated with V. dahliae alone. The early introduction of V. tricorpus in soil-drench inoculations appeared to provide better relief from subsequent V. dahliae inoculation than when the two species were co-inoculated simultaneously using the root-dip method, suggesting competitive exclusion as a plausible mechanism. A spore-polymerase chain reaction assay developed using cultured spores directly as template and primers specific to V. tricorpus confirmed the presence of V. tricorpus on inoculated roots. This work demonstrates the potential use of V. tricorpus to directly reduce the effect of V. dahliae on lettuce and artichoke and, to our knowledge, is the first reported characterization of V. tricorpus isolates collected from lettuce and artichoke.

Sequential inoculation versus co-inoculation in Cabernet Franc wine fermentation

A study has been carried out in order to determine the effect of the lactic acid bacteria inoculation time on the kinetic of vinification and on chemical and sensory characteristics of Cabernet Franc wines. Traditional vinifications, with lactic acid bacteria inoculated after completion of alcoholic fermentation were compared with vinifications where yeast and bacteria were co-inoculated at the beginning of vinification. One commercial yeast strain and an autochthonous Oenococcus oeni strain (C22L9), previously identified and selected at our laboratory, were used. Monitoring of alcoholic and malolactic fermentations was carried out by yeast and lactic acid bacteria counts and by measuring l-malic acid concentration. Wines were chemically characterized and analysed for volatile compounds content. A sensory analysis, consisting of a descriptive and a triangular test, was also carried out. Results from this study showed that the concurrent yeast/bacteria inoculation of musts at the beginning of vinification produced a reduction in duration of the process without an excessive increase in volatile acidity. Differences in volatile compounds content and the corresponding impact on the sensorial profile of wines were also displayed. These results suggest that co-inoculation is a worthwhile alternative for winemaking of Cabernet Franc wines, if compared with traditional post-alcoholic fermentation lactic acid bacteria inoculation.

Managing your wine fermentation to reduce the risk of biogenic amine formation

Biogenic amines are nitrogenous organic compounds produced in wine from amino acid precursors mainly by microbial decarboxylation. The concentration of biogenic amines that can potentially be produced is dependent on the amount of amino acid precursors in the medium, the presence of decarboxylase positive microorganisms and conditions that enable microbial or biochemical activity such as the addition of nutrients to support the inoculated starter cultures for alcoholic and malolactic fermentation (MLF). MLF can be conducted using co-inoculation or an inoculation after the completion of alcoholic fermentation that may also affect the level of biogenic amines in wine. This study focused on the impact of the addition of complex commercial yeast and bacterial nutrients and the use of different MLF inoculation scenarios on the production of biogenic amines in wine. Results showed that the addition of complex nutrients to real grape must could potentially increase histamine concentrations in wine. The same experiment in synthetic grape must showed a similar trend for putrescine and cadaverine. The effect of different MLF inoculation scenarios was examined in two cultivars, Pinotage and Shiraz. Conflicting results was obtained. In the Shiraz, co-inoculation resulted in lower biogenic amine concentrations after MLF compared to before MLF, while the concentration was higher in the Pinotage. However, the production of biogenic amines was affected more by the presence of decarboxylase positive lactic acid bacteria than by the addition of complex nutrients or the inoculation scenario.

Complementary Effects of Dark Septate Endophytes and Trichoderma Strains on Growth and Active Ingredient Accumulation of Astragalus mongholicus under Drought Stress

Drought is a major abiotic stress factor affecting plant growth and production, while utilizing beneficial endophytic fungi is one of the most promising strategies for enhancing plant growth and drought tolerance. In the current study, a pot experiment was conducted to investigate the beneficial effects of dark septate endophyte (DSE) (Macrophomina pseudophaseolina, Paraphoma radicina) and Trichoderma (Trichoderma afroharzianum, Trichoderma longibrachiatum) inoculum on Astragalus mongholicus grown in sterile soil under drought stress, alone, or in combination. The addition of Trichoderma enhanced the DSE colonization in roots regardless of the water condition. Under well-watered conditions, M. pseudophaseolina inoculation significantly enhanced the biomass and root length of A. mongholicus. The two DSE and Trichoderma inoculum significantly improved calycosin-7-O-β-D-glucoside content. However, M. pseudophaseolina + T. afroharzianum inoculation better promoted root growth, whereas co-inoculation had higher active ingredient contents compared with single inoculation, except for P. radicina + T. afroharzianum. Under drought stress, DSE and Trichoderma inoculum significantly improved root biomass, root length, calycosin-7-O-β-D-glucoside content, and activities of nitrate reductase and soil urease. P. radicina + T. afroharzianum and P. radicina + T. longibrachiatum better increased root length, and all combinations of DSE and Trichoderma had a greater impact on the increase in formononetin content compared with the single treatments. Additionally, Trichoderma relies on antioxidant enzymes, growth hormones, and the redox system (ascorbic acid−glutathione) to resist drought, while DSE strains have an additional osmotic regulation system in addition to the drought resistance function possessed by Trichoderma, and the effect of co-inoculation (especially M. pseudophaseolina + T. longibrachiatum and P. radicina + T. afroharzianum) on plant physiological parameters was greater than that of single inoculation. This study provides a new research direction for the effects of DSE and Trichoderma on medicinal plant cultivated in dryland.

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

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

Product and Microbial Population Kinetics During Balsamic-Styled Vinegar Production

Balsamic-styled vinegar is a nutraceutical product obtained from a two-stage fermentation process of grape must. However, little is known about how fermentation conditions affect growth kinetics, bio-product development, population dynamics and the final product quality. As a result, the current study investigated the effect of fermentation temperature and inoculation strategy on the fermentation dynamics of Balsamic-styled vinegar production. A microbial consortium of non-Saccharomyces yeasts (n = 13) and acetic acid bacteria (n = 5) was tested at various fermentation temperatures (22 °C, 28 °C and a fluctuating temperature regimen). Different inoculation strategies (co-inoculation and sequential inoculation) were investigated, and population dynamics of the product selected due to a rapid fermentation period were confirmed using a 16S and 18S gene sequencing. A higher fermentation temperature (28 °C) and co-inoculation strategy resulted in a shorter fermentation cycle, whilst the desired acetic acid concentration of 60 g/L was achieved within 38 days. 16S and 18S gene sequencing showed that 50.84% of Acetobacter species were abundant at the end of the fermentation cycle, while 40.18% bacteria were unculturable. The study provides a better understanding of how fermentation temperature and inoculation strategy affect the fermentation period, population dynamics and the growth kinetics of the microbial consortium during the production of Balsamic-styled vinegar. PRACTICAL APPLICATION: Lower quality South African wine grapes could be channelled to an alternative high-priced product (Balsamic-styled vinegar), with low technological input requirements. Thus, making it easier to incorporate a low capital start-up business while empowering small business entrepreneurs and boosting the economy.

Profound Change in Soil Microbial Assembly Process and Co-occurrence Pattern in Co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 on Soybean

Rhizosphere microbial communities are vital for plant growth and soil sustainability; however, the composition of rhizobacterial communities, especially the assembly process and co-occurrence pattern among microbiota after the inoculation of some beneficial bacteria, remains considerably unclear. In this study, we investigated the structure of rhizomicrobial communities, their assembly process, and interactions contrasting when Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 are co-inoculated or Bradyrhizobium japonicum 5038 mono-inoculated in black and cinnamon soils of soybean fields. The obtained results indicated that the Chao and Shannon indices were all higher in cinnamon soil than that in black soil. In black soil, the co-inoculation increased the Shannon indices of bacteria comparing with that of the mono-inoculation. In cinnamon soil, the co-inoculation decreased the Chao indices of fungi comparing with that of mono-inoculation. Compared with the mono-inoculation, the interactions of microorganisms of co-inoculation in the co-occurrence pattern increased in complexity, and the nodes and edges of co-inoculation increased by 10.94, 40.18 and 4.82, 16.91% for bacteria and fungi, respectively. The co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 increased the contribution of stochastic processes comparing with Bradyrhizobium japonicum 5038 inoculation in the assembly process of soil microorganisms, and owing to the limitation of species diffusion might restrict the direction of pathogenic microorganism movement. These findings support the feasibility of rebuilding the rhizosphere microbial system via specific microbial strain inoculation and provide evidence that the co-inoculation of Bradyrhizobium japonicum 5038 and Bacillus aryabhattai MB35-5 can be adopted as an excellent compound rhizobia agent resource for the sustainable development of agriculture.

Inoculation With Indigenous Rhizosphere Microbes Enhances Aboveground Accumulation of Lead in Salix integra Thunb. by Improving Transport Coefficients

The application of plant-microbial remediation of heavy metals is restricted by the difficulty of exogenous microbes to form large populations and maintain their long-term remediation efficiency. We therefore investigated the effects of inoculation with indigenous heavy-metal-tolerant rhizosphere microbes on phytoremediation of lead (Pb) by Salix integra. We measured plant physiological indexes and soil Pb bioavailability and conducted widespread targeted metabolome analysis of strains to better understand the mechanisms of enhance Pb accumulation. Growth of Salix integra was improved by both single and co-inoculation treatments with Bacillus sp. and Aspergillus niger, increasing by 14% in co-inoculated plants. Transfer coefficients for Pb, indicating mobility from soil via roots into branches or leaves, were higher following microbial inoculation, showing a more than 100% increase in the co-inoculation treatment over untreated plants. However, Pb accumulation was only enhanced by single inoculation treatments with either Bacillus sp. or Aspergillus niger, being 10% greater in plants inoculated with Bacillus sp. compared with uninoculated controls. Inoculation mainly promoted accumulation of Pb in aboveground plant parts. Superoxide dismutase and catalase enzyme activities as well as the proline content of inoculated plants were enhanced by most treatments. However, soil urease and catalase activities were lower in inoculated plants than controls. Proportions of acid-soluble Pb were 0.34 and 0.41% higher in rhizosphere and bulk soil, respectively, of plants inoculated with Bacillus sp. than in that of uninoculated plants. We identified 410 metabolites from the microbial inoculations, of which more than 50% contributed to heavy metal bioavailability; organic acids, amino acids, and carbohydrates formed the three major metabolite categories. These results suggest that both indigenous Bacillus sp. and Aspergillus niger could be used to assist phytoremediation by enhancing antioxidant defenses of Salix integra and altering Pb bioavailability. We speculate that microbial strains colonized the soil and plants at the same time, with variations in their metabolite profiles reflecting different living conditions. We also need to consider interactions between inocula and the whole microbial community when applying microbial inoculation to promote phytoremediation.

Effects of Bradyrhizobium Co-Inoculated with Bacillus and Paenibacillus on the Structure and Functional Genes of Soybean Rhizobacteria Community

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve soil nutrients and promote plant growth and health. However, the growth-promoting effect of a single PGPR on plants is limited. Here, we evaluated the effect of applying rhizobium Bradyrhizobium japonicum 5038 (R5038) and two PGPR strains, Bacillus aryabhattai MB35-5 (BA) and Paenibacillus mucilaginosus 3016 (PM), alone or in different combinations on the soil properties and rhizosphere bacterial community composition of soybean (Glycine max). Additionally, metagenomic sequencing was performed to elucidate the profile of functional genes. Inoculation with compound microbial inoculant containing R5038 and BA (RB) significantly improved nodule nitrogenase activity and increased soil nitrogen content, and urease activity increased the abundance of the nitrogen cycle genes and Betaproteobacteria and Chitinophagia in the rhizosphere. In the treatment of inoculant-containing R5038 and PM (RP), significant changes were found for the abundance of Deltaproteobacteria and Gemmatimonadetes and the phosphorus cycle genes, and soil available phosphorus and phosphatase activity were increased. The RBP inoculants composed of three strains (R5038, BA and PM) significantly affected soybean biomass and the N and P contents of the rhizosphere. Compared with RB and RP, RBP consistently increased soybean nitrogen content, and dry weight. Overall, these results showed that several PGPR with different functions could be combined into composite bacterial inoculants, which coordinately modulate the rhizosphere microbial community structure and improve soybean growth.

Functional Transcomplementation between Wheat Dwarf Virus Strains in Wheat and Barley

Wheat dwarf virus, transmitted by the leafhopper Psammotettix alienus in a persistent, non-propagative manner, infects numerous species from the Poaceae family. Data associated with wheat dwarf virus (WDV) suggest that some isolates preferentially infect wheat while other preferentially infect barley. This allowed to define the wheat strain and the barley strain. There are contradictory results in the literature regarding the ability of each of these two strains to infect its non-preferred host. To improve knowledge on the interactions between WDV strains and barley and wheat, transmission experiments were carried out using barcoded P. alienus and an experimental design based on single/sequential acquisitions of WDV strains and on transmissions to wheat and barley. Results showed that (I) WDV strains are transmitted with similar efficiencies by P. alienus males, females and larvae, (II) WDV wheat and barley strains do not infect barley and wheat plants, respectively, and (III) a functional transcomplementation between the wheat and barley strains allows a mixed infection of barley and wheat. The described ability of each WDV strain to infect a non-host plant in the presence of the other viral strain must be considered to analyze data available on WDV host range.

Influence on Soybean Aphid by the Tripartite Interaction between Soybean, a Rhizobium Bacterium, and an Arbuscular Mycorrhizal Fungus

The inoculation of arbuscular mycorrhizal (AM) fungi and rhizobia in legumes has been proven to increase plant growth and yield. To date, studies of the effects of these interactions on phytophagous insects have shown them to be context-dependent depending on the inoculant strain, the plant, and the insect species. Here, we document how a symbiosis involving an AM fungus, Rhizophagus irregularis; a rhizobium, Bradyrhizobium japonicum; and soybean, Glycine max, influences the soybean aphid, Aphis glycines. Soybean co-inoculated with the AM fungus–rhizobium pair increased the plant’s biomass, nodulation, mycorrhizal colonization, nitrogen, and carbon concentrations, but decreased phosphorus concentration. Similar effects were observed with rhizobium alone, with the exception that root biomass was unaffected. With AM fungus alone, we only observed an increase in mycorrhizal colonization and phosphorus concentration. The aphids experienced an increased reproductive rate with the double inoculation, followed by rhizobium alone, whereas no effect was observed with the AM fungus. The size of individual aphids was not affected. Furthermore, we found positive correlation between nitrogen concentration and aphid population density. Our results confirm that co-inoculation of two symbionts can enhance both plant and phytophagous insect performance beyond what either symbiont can contribute alone.

Quorum sensing communication: Bradyrhizobium-Azospirillum interaction via N-acyl-homoserine lactones in the promotion of soybean symbiosis

Quorum-sensing (QS) mechanisms are important in intra- and inter-specific communication among bacteria. We investigated QS mechanisms in Bradyrhizobium japonicum strain CPAC 15 and Azospirillum brasilense strains Ab-V5 and Ab-V6, used in commercial co-inoculants for the soybean crop in Brazil. A transconjugant of CPAC 15-QS with partial inactivation of N-acyl-homoserine lactones (AHLs) was obtained and several parameters were evaluated; in vitro, CPAC 15 and the transconjugant differed in growth, but not in biofilm formation, and no differences were observed in the symbiotic performance in vivo. The genome of CPAC 15 carries functional luxI and luxR genes and low amounts of three AHL molecules were detected: 3-OH-C12-AHL, 3-OH-C14-AHL, and 3-oxo-C14-AHL. Multiple copies of luxR-like genes, but not of luxI are present in the genomes of Ab-V5 and Ab-V6, and differences in gene expression were observed when the strains were co-cultured with B. japonicum; we may infer that the luxR-genes of A. brasilense may perceive the AHL molecules of B. japonicum. Soybean symbiotic performance was improved especially by co-inoculation with Ab-V6, which, contrarily to Ab-V5, did not respond to the AHLs of CPAC 15. We concluded that A. brasilense Ab-V5, but not Ab-V6, responded to the QS signals of CPAC 15, and that the synergistic interaction may be credited, at least partially, to the QS interaction. In addition, we confirmed inter- and intra-species QS communication between B. japonicum and A. brasilense and, for Azospirillum, at the strain level, impacting several steps of the symbiosis, from cell growth to plant nodulation and growth.

Plant-microbe-microbe interactions influence the faba bean nodule colonization by diverse endophytic bacteria

Legume root nodules harbor rhizobia and other non-nodulating endophytes known as nodule-associated bacteria (NAB) whose role in the legume symbiosis is still unknown. We analysed the genetic diversity of 34 NAB isolates obtained from the root nodules of faba bean grown under various soil conditions in Egypt using 16S rRNA and concatenated sequences of three housekeeping genes. All isolates were identified as members of the family Enterobacteriaceae belonging to the genera Klebsiella, Enterobacter and Raoultella. We identified nine enterobacterial genospecies, most of which have not been previously reported as NAB. All isolated strains harbored nifH gene sequences and most of them possessed plant growth-promoting (PGP) traits. Upon co-inoculation with an N2 fixing rhizobium (Rlv NGB-FR128), two strains (Enterobacter sichanensis NGB-FR97 and Klebsiella variicola NGB-FR116) significantly increased nodulation, growth and N-uptake of faba bean plants over the single treatments or the uninoculated control. The presence of these enterobacteria in nodules was significantly affected by the host plant genotype, symbiotic rhizobium genotype and endophyte genotype, indicating that the nodule colonization process is regulated by plant-microbe-microbe interactions. This study emphasizes the importance of nodule-associated enterobacteria and suggests their potential role in improving the effectiveness of rhizobial inoculants.

Synergetic Effect of Metschnikowia pulcherrima and Lachancea thermotolerans in Acidification and Aroma Compounds in Airén Wines

On the one hand, the species Lachancea thermotolerans is known for its high genetic diversity, allowing for the existence of strains that produce high concentrations of lactic acid. In contrast, the species Metschnikowia pulcherrima is renowned for its high enzymatic activity capable of producing aromatic esters during fermentation. By enhancing acidity and boosting the concentration of aromatic compounds, both species are currently used to enhance the organoleptic profile of wines. In this regard, ternary fermentations with M. pulcherrima and L. thermotolerans were carried out and the wines produced were further analysed with GC-FID, FTIR, and UV-Vis spectrophotometry. The outcomes showed that the species M. pulcherrima favored an increase in ethyl lactate (between 37 and 41 mg/L) along with an increased concentration of 2-phenylethyl alcohol (between 30 and 35 mg/L), whereas the species L. thermotolerans was able to produce 1 g/L of lactic acid in ternary fermentations. Additionally, pH levels were slightly lower in these fermentations and the color of the white wines produced showed less chemical oxidation as hue values were lower than the control. Finally, the ternary fermentations of L. thermotolerans and M. pulcherrima had higher overall rating in the tasting. In conclusion, ternary fermentations involving these two non-Saccharomyces species are suggested as a substitute for spontaneous fermentations in the production of wines from neutral varieties to express freshness more vividly. This biotechnology may be further favored by the possibility of applying emerging technologies for the removal of microorganisms in grapes and musts.

Enhanced pathogenicity of Leptosphaeria maculans Pycnidiospores from paired co-inoculation of Brassica napus cotyledons with ascospores

BACKGROUND AND AIMS

Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus) worldwide, including Australia. In most cases, the severity of the disease in the field is related to infections caused by airborne ascospores. In contrast, pycnidiospores originating from leaf and stem lesions and stubble are widely assumed to play only a relatively minor role in the epidemiology of blackleg. It is not clear whether, under certain conditions, pycnidiospores can cause severe disease in the field. The aim of the work reported was to determine if the pathogenicity of pycnidiospores is enhanced by paired co-inoculation of B. napus cotyledons with ascospores.

METHODS

Three investigations were carried out under controlled-environment conditions using various L. maculans isolates and B. napus cultivars with different levels of host resistance to blackleg.

KEY RESULTS

In all three experiments, co-inoculation with ascospores increased the ability of pycnidiospores to cause more disease on B. napus than when inoculations consisted of pycnidiospores alone. This effect was significantly influenced by the host resistance of the cultivar, but overall was independent of the L. maculans isolate used in the different experiments. This effect was also independent of timing of inoculation with the ascospores, with increased disease from pycnidiospores occurring on the cotyledon of the seedling in situations where inoculations with ascospores were carried out 0, 1 or 2 d after pycnidiospore inoculation. This enhanced pathogenicity of pycnidiospores was evident even when low concentrations of pycnidiospores were applied to the other cotyledon of the same seedling.

CONCLUSIONS

These results may explain continuing severe blackleg disease cycles throughout the cropping season even when ascospore fallout was low or constrained only to a brief period or phase of the cropping season, and suggest that disease epidemics may be polycyclic rather than monocyclic.

Varying Inocula Permutations (Aspergillus oryzae and Bacillus amyloliquefaciens) affect Enzyme Activities and Metabolite Levels in Koji

In this study, we investigated the altered enzymatic activities and metabolite profiles of koji fermented using varying permutations of Aspergillus oryzae and/or Bacillus amyloliquefaciens. Notably, the protease and β-glucosidase activities were manifold increased in co-inoculated (CO) koji samples (co-inoculation of A. oryzae and B. amyloliquefaciens). Furthermore, gas chromatography-mass spectrometry (GC-MS)-based metabolite profiling indicates that levels of amino acids, organic acids, sugars, sugar alcohols, fatty acids, nucleosides, and vitamins were distinctly higher in CO, SA (sequential inoculation of A. oryzae, followed by B. amyloliquefaciens), and SB (sequential inoculation of B. amyloliquefaciens, followed by A. oryzae). The multivariate principal component analysis (PCA) plot based on GC-MS datasets indicated a clustered pattern for MA and MB (koji samples inoculated either with A. oryzae or B. amyloliquefaciens) across PC2 (20.0%). In contrast, the CO, SA, and SB metabolite profiles displayed segregated patterns across PLS1 (22.2%) and PLS2 (21.1%) in the partial least square discriminant analysis (PLS-DA) model. Intriguingly, the observed disparity in the levels of primary metabolites was engendered largely by higher relative levels of sugars and sugar alcohols in MA, SA, and CO koji samples, which was commensurate with the relative amylase activities in respective samples. Collectively, the present study emphasizes the utility of integrated biochemical and metabolomic approaches for achieving the optimal permutation of fermentative inocula for industrial koji preparation.

The Effectiveness of Co-Inoculation by Consortia of Microorganisms Depends on the Type of Plant and the Soil Microbiome

The amalgamation of mineral and targeted bacterial preparations represents a new generation of agricultural technology. Inoculation with combined preparations of microorganisms is more effective than inoculation with a single microorganism in stimulating plant growth by providing a more balanced diet for various crops. In this work, the effect of inoculation of 20 consortium variants on the yield indicators of three crops (wheat, buckwheat, corn) and the soil microbiome in the open field was investigated. The soil microbiome was defined by 16S rRNA sequences through NGS. The species richness of the soil microbial community (alpha diversity) was similar for all studied samples. A beta-diversity analysis revealed that the microbial diversity of three soil samples (C.bw, F.bw and Soil.bw) differed significantly from all others. At the phylum level, the number of Acidobacteriota and Firmicutes in these samples was increased. For the combination "Consortium C (Rothia endophytic GMG9 and Azotobacter chroococcum GMG39)-buckwheat", a systemic positive improvement in all growth and yield indicators was observed. The soil of the site where buckwheat grew, inoculated by Consortium C, contained significantly more available phosphorus than all other soil samples. Such results can be explained both by the direct action of a consortium of phosphate-immobilizing and nitrogen-fixing bacteria and acidification of the medium due to an increase in phylum Acidobacteriota bacteria in the soil.

Effects of biosurfactant-producing bacteria on biodegradation and transport of phenanthrene in subsurface soil

This study investigated the effects of surfactant-producing microorganism, Pseudomonas aeruginosa ATCC 9027, on phenanthrene (PHE) biodegradation by two different PHE-degrading bacteria (Isolate P5-2 and Pseudomonas strain R) in soil. Phenanthrene mineralization experiments were conducted with soils inoculated with one of PHE-degraders and/or the surfactant-producer. Influence of co-inoculation with the surfactant-producing bacteria on phenanthrene transport and biodegradation was also examined in soil columns. P. strain R mineralized phenanthrene faster and to a greater extent than Isolate P5-2 in the test soil. Co-inoculation with the surfactant-producing bacteria significantly enhanced phenanthrene biodegradation by P. strain R but it did not affect the biodegradation by Isolate P5-2 in both batch and column systems. Production of biosurfactants by P. aeruginosa ATCC 9027 was negligible under the given conditions. This study demonstrated that bioaugmentation with surfactant-producing bacteria could enhance in situ bioremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and the beneficial effect of the bioaugmentation depended on types of PAH-degrading microorganisms present.

Remediation of copper-contaminated soils using Tagetes patula L., earthworms and arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) and earthworms have potential uses in the bioremediation of contaminated soils. In recent years, heavy metal-contaminated sites have been remediated by adding plants and AMF or earthworms to the soil. However, there are few studies on remediation using combinations of plants, animals, and microbes, especially for the remediation of Cu-contaminated soil. The present study investigated the separate and combined effects of AMF and earthworms on Cu-contaminated soil in which Tagetes patula L. was grown. The results show that the combined application of AMF and earthworms markedly increased the biomass of plant shoots and roots by more than 100%. It also increased Cu extraction by T. patula by 270%. The combined treatment was effective in increasing the CEC, contents of OM, and available Cu, P and K, but reduced the soil pH. Furthermore, the combined treatment significantly increased the abundance and diversity of the soil microbial community. In particular, the abundances of the bacteria Bacteroides, Proteobacteria, and Actinobacteria were increased, with the genera Flavobacterium, Pedobacter, Algoriphagus, Gaetbulibacter, Pseudomonas, Luteimonas, and Arthrobacter dominating. Meanwhile, the abundance of the fungus Zygomycota was increased, with Mortierella dominating. Moreover, inoculation with earthworms greatly improved the structure of the soil microbial community.