Rhizospheric Strains Research Articles

New Observation in Biocontrol of Penicillium caperatum against Fusarium oxysporum on Saposhnikovia divaricata and as a Plant Growth Promoter

Fusarium oxysporum, a common fungal pathogen that infects economic crops, causes Fusarium wilt disease to Saposhnikovia divaricata at an annual incidence rate of more than 15%. This study aimed to assess the potential of rhizospheric fungi as antifungal agents against Fusarium wilt of Saposhnikovia divaricata. In this study, 104 fungi were isolated from S. divaricata rhizospheric soil. Twelve rhizospheric strains that showed antagonistic activity against F. oxysporum, MR-16, MR-32, MR-38, etc., were screened out. Biocontrol activities of the twelve strains, especially MR-16, were subsequently characterized and evaluated. Strain MR-16 as potential stock for biocontrol had good antibiotic activity against F. oxysporum in vitro experiment. Based on the analysis of morphological properties and rDNA internal transcribed spacers (ITS), we identified an isolate MR-16 as Penicillium caperatum (GenBank No. OK287146.1), a new record of this species of China. The results of the in vitro antagonistic assay indicated that the conidial germination rate was significantly decreased, and the mycelia morphology of F. oxysporum induced change via the culture filtrate of P. caperatum MR-16, such as deformation and degradation. In an outdoor pot experiment, inoculation of S. divaricata plants with F. oxysporum created severe wilting symptoms; however, in inoculation trials, MR-16 effectively suppressed disease lesions, with a strong control efficacy of 60.76%. In addition, strain MR-16 could successfully colonize and form stable populations in the soil, and it showed a continuous positive growth-promoting effect on S. divaricata plants.

Comparative study of the rhizosphere microbiome of Coffea arabica grown in different countries reveals a small set of prevalent and keystone taxa

Coffee (Coffea arabica) is a globally important crop and its cultivation demands the use of agrochemicals and pesticides. Recently, plant-associated microorganisms have emerged as an unexploited resource to enhance crop performance and sustainability. In particular, the rhizosphere microbiome has been identified as a hotspot for plant health, by providing tolerance to biotic and abiotic stresses as well as regulating phenological traits. However, its composition varies widely across crops and environmental conditions. Hence, the knowledge of the “common core” taxa, which are a subset of the microbiome that is persistently associated, across different environmental gradients and conditions, to a host species, represent valuable targets for the development of microbiome-based management approaches. This study aimed to characterize and determine the rhizosphere-inhabiting microbial groups (common core and most prevalent taxa), associated with the Coffea arabica plants in different geographical locations. To assess the structure of the coffee rhizosphere microbiome, we performed the 16 S rRNA amplicon analysis of samples collected across six locations spanning four countries and grown under different climate conditions, soil type, agroecosystem management, plant vegetative stage and age. Our findings allowed us to delineate and identify a robust set of six bacterial taxa, namely Sphingobium, Rhizobium group, Acidibacter, Sphingomonas, Burkholderia group and Amycolatopsis, which are likely to play an important role for the growth and health of coffee plants. Using network analysis, we observed that some of the six “common core” taxa were highly interconnected with the resident community, being also keystone taxa of the coffee rhizosphere microbiome. Furthermore, we performed a high-throughput targeted isolation resulting into 162 rhizosphere bacterial strains, some of them related to the most prevalent taxa. These isolates represent a working bacterial culture collection to be used in the future for the development of microbiome-based solutions for a more sustainable coffee farming.

Interplay between rhizospheric Pseudomonas chlororaphis strains lays the basis for beneficial bacterial consortia.

Pseudomonas chlororaphis (Pc) representatives are found as part of the rhizosphere-associated microbiome, and different rhizospheric Pc strains frequently perform beneficial activities for the plant. In this study we described the interactions between the rhizospheric Pc strains PCL1601, PCL1606 and PCL1607 with a focus on their effects on root performance. Differences among the three rhizospheric Pc strains selected were first observed in phylogenetic studies and confirmed by genome analysis, which showed variation in the presence of genes related to antifungal compounds or siderophore production, among others. Observation of the interactions among these strains under lab conditions revealed that PCL1606 has a better adaptation to environments rich in nutrients, and forms biofilms. Interaction experiments on plant roots confirmed the role of the different phenotypes in their lifestyle. The PCL1606 strain was the best adapted to the habitat of avocado roots, and PCL1607 was the least, and disappeared from the plant root scenario after a few days of interaction. These results confirm that 2 out 3 rhizospheric Pc strains were fully compatible (PCL1601 and PCL1606), efficiently colonizing avocado roots and showing biocontrol activity against the fungal pathogen Rosellinia necatrix. The third strain (PCL1607) has colonizing abilities when it is alone on the root but displayed difficulties under the competition scenario, and did not cause deleterious effects on the other Pc competitors when they were present. These results suggest that strains PCL1601 and PCL1606 are very well adapted to the avocado root environment and could constitute a basis for constructing a more complex beneficial microbial synthetic community associated with avocado plant roots.

Bio-Functionalized Manganese Nanoparticles Suppress Fusarium Wilt in Watermelon (Citrullus lanatus L.) by Infection Disruption, Host Defense Response Potentiation, and Soil Microbial Community Modulation.

The use of nanofabricated materials is being explored for the potential in crop disease management. Chemically synthesized micronutrient nanoparticles (NPs) have been shown to reduce crop diseases; however, the potential of biogenic manganese NPs (bio-MnNPs) in disease control is unknown. Here, the potential and mechanism of bio-MnNPs in suppression of watermelon Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum (Fon) are reported. Bio-MnNPs are synthesized by cell-free cultural filtrate of a waterrmelon rhizosphere bacterial strain Bacillus megaterium NOM14, and are found spherical in shape with a size range of 27.0-65.7nm. Application of bio-MnNPs at 100µg mL-1 increases Mn content in watermelon roots/shoots and improves growth performance through enhancing multiple physiological processes, including antioxidative capacity. Bio-MnNPs at 100 µg mL-1 suppress Fusarium wilt through inhibiting colonization and invasive growth of Fon in watermelon roots/stems, and inhibit Fon vegetative growth, conidiation, conidial morphology, and cellular integrity. Bio-MnNPs potentiate watermelon systemic acquired resistance by triggering the salicylic acid signaling upon Fon infection, and reshape the soil microbial community by improving fungal diversity. These findings demonstrate that bio-MnNPs suppress watermelon Fusarium wilt by multiple ex planta and in planta mechanisms, and offer a promising nano-enabled strategy for the sustainable management of crop diseases.

Draft Genome Sequence of Bacillus halotolerans IcBac2.1, a Strain with Potential as a Phytopathogen Control Agent.

Several species of the genus Bacillus are used as plant growth-promoting bacteria. In particular, species of the subtilis group are known as good antagonists of phytopathogenic fungi. Here, we report the draft genome sequence of a rhizospheric Bacillus strain with promising abilities as a biocontrol agent.

Exploring plant growth-promoting, biocatalytic, and antimicrobial potential of salt tolerant rhizospheric Georgenia soli strain TSm39 for sustainable agriculture.

To explore the in vivo and in vitro plant growth promoting activities, biocatalytic potential, and antimicrobial activity of salt tolerance rhizoactinobacteria, rhizospheric soil of a halotolerant plant Saueda maritima L. was collected from Rann of Tiker, near Little Rann of Kutch, Gujarat (India). The morphology analysis of the isolated strain TSm39 revealed that the strain belonged to the phylum actinobacteria, as it was stained Gram-positive, displayed filamentous growth, showed spore formation and red pigment production on starch casein agar (SCA). It was identified as Georgenia soli based on 16S rRNA gene sequencing. The Georgenia soli strain TSm39 secreted extracellular amylase, pectinase, and protease. It showed in vitro plant growth-promoting (PGP) activities such as indole acetic acid (IAA) production, siderophore production, ammonia production, and phosphate solubilization. In vivo plant growth-promoting traits of strain TSm39 revealed 30% seed germination on water agar and vigor index 374.4. Additionally, a significant increase (p ≤ 0.05) was found in growth parameters such as root length (16.1 ± 0.22), shoot length (15.2 ± 0.17), the fresh weight (g), and dry weight (g) of the roots (0.43 ± 0.42 and 0.32 ± 0.12), shoots (0.62 ± 0.41 and 0.13 ± 0.03), and leaves (0.42 ± 0.161 and 0.14 ± 0.42) in treated seeds of Vigna radiata L. plant with the strain TSm39 compared to control. The antibiotic susceptibility profile revealed resistance of the strain TSm39 to erythromycin, ampicillin, tetracycline, and oxacillin, while it displayed maximum sensitivity to vancomycin (40 ± 0.72), chloramphenicol (40 ± 0.61), clarithromycin (40 ± 1.30), azithromycin (39 ± 0.42), and least sensitivity to teicoplanin (15 ± 0.15). Moreover, the antimicrobial activity of the strain TSm39 was observed against Gram's positive and Gram's negative microorganisms such as Shigella, Proteus vulgaris, and Bacillus subtilis. These findings indicated that the Georgenia soli strain TSm39 has multiple plant-growth-promoting properties and biocatalytic potential that signifies its agricultural applications in the enhancement of crop yield and quality and would protect the plant against plant pathogens.

Enhancement of Green Soybean Growth and Yield in Alluvial Soil by Potent N2-fixing Rhizospheric Bacteria

<b>Background and Objective:</b> Nitrogen fertilizer causes adverse effects on the environment aspect, so biological nitrogen sources should be applied in agriculture. The objective of the study was to evaluate the efficacy of N<sub>2</sub>-fixing rhizospheric bacteria in improving soil fertility, nitrogen (N) uptake, growth and yield of green soybean (<i>Glycine max</i> (L.) Merr). <b>Materials and Methods:</b> The pot experiment was conducted with 9 treatments (i) 100% N of recommendation of fertilizer formula (RFF), (ii) 85% N, (iii) 70% N, (iv) 55% N, (v) 85% N and a mixture of <i>Enterobacter cloacae</i> ASD-07 and ASD-28, (vi) 70% N and a mixture of ASD-07 and ASD-28, (vii) 55% N and a mixture of ASD-07 and ASD-28, (viii) 0% N and ASD-07 and ASD-28, and (ix) 0% N, without bacteria<i>,</i> with four replications in in-dyke alluvial soil collected from Chau Phu District, An Giang Province. <b>Results:</b> The use of a mixture of the two N<sub>2</sub>-fixing rhizospheric strains<i> </i>as biofertilizers at 85% N level improved NH<sub>4</sub><sup>+</sup> content and N uptake with an increase of 3.1 mg kg<sup></sup><sup>1</sup> and 95.8 mg pot<sup></sup><sup>1</sup>, respectively. They also produced higher values in growth including plant height, number of leaves, stem diameter and yield components including pod number, pod diameter, seed length, seed diameter and seed thickness. <b>Conclusion:</b> The application of a mixture of the two N<sub>2</sub>-fixing rhizospheric strains resulted in replacing 15% N of RFF, but it still improved the yield.

Rhizosphere Bacteria From Panax notoginseng Against Meloidogyne hapla by Rapid Colonization and Mediated Resistance.

Root-knot nematodes (RKNs) are soil-borne pathogens that severely affect Panax notoginseng growth and productivity. Thus, there is an urgent need for biological control agents or green nematicides to control root-knot nematodes. Rhizosphere bacteria can effectively control RKNs through different mechanisms. In this study, the three rhizosphere Bacillus strains, isolated from the root of P. notoginseng, were evaluated for the nematicidal activity and biological control efficacy against root-knot nematodes. In addition, we also evaluated the colonization ability of the two bacterial strains with significant biocontrol effect and dynamic regulation of genes related to systemic resistance in P. notoginseng. The rhizosphere Bacillus velezensis GJ-7 and Bacillus cereus NS-2 showed high nematicidal activity against Meloidogyne hapla in vitro and significantly reduced the number of root galls in three different control experiments. The results of colonization experiments showed that the strains GJ-7 and NS-2 colonized P. notoginseng root rapidly and stably. Additionally, the colonization of the strains NS-2 and GJ-7 activated the defense-responsive genes in P. notoginseng. These results indicated that the B. cereus strain NS-2 and B. velezensis strain GJ-7 have the potential for successful ecological niche occupation and enhance plant resistance and therefore could be considered as potential biocontrol agents against root-knot nematodes.

The impact of newly synthesized sulfonamides on soil microbial population and respiration in rhizospheric soil of wheat (Triticum aestivum L.).

Antibiotics released into agricultural fields through the manure of grazing animals could exert harmful impacts on soil microbes and plants. Antibiotics exert high impacts on environment than other pharmaceuticals due to their higher biological activity. However, little is known about their impacts on plants, despite indications that antibiotics exert negative effects on soil microorganisms, which ultimately harm the plants. It has been demonstrated that beneficial microorganisms promote plant growth and development under various stresses. This study evaluated the toxicity of four newly derived sulfonamides (SAs), i.e., 2-(phenylsulfonyl) hydrazine carbothioamide (TSBS-1), N, 2-bis phenyl hydrazine carbothioamide (TSBS-2), aminocarbonyl benzene sulfonamide (UBS-1), and N, N’-carbonyl dibenzene sulfonamide (UBS-2) on bacterial growth and soil microbial respiration. Each SA was tested at four different concentrations (i.e., 2.25, 2.5, 3, 4 mg/ml) against five rhizospheric bacterial strains, including AC (Actinobacteria sp.), RS-3a (Bacillus sp.), RS-7a (Bacillus subtilis), RS-4a (Enterobacter sp.), and RS-5a (Enterobacter sp.). Antimicrobial activity was checked by disc diffusion method, which showed that inhibition zone increased with increasing concentration of SAs. The UBS-1 resulted in the highest inhibition zone (11.47 ± 0.90 mm) against RS-4a with the highest concentration (4 mg/ml). Except TSBS-1, all sulfonamide derivatives reduced CO2 respiration rates in soil. Soil respiration values significantly increased till 6th day; however, exposure of sulfonamide derivatives suppressed microbial respiration after 6th day. On the 20th day, poor respiration activity was noted at 0.23, 0.2, and 0.4 (CO2 mg/g dry soil) for TSBS-1, UBS-1, and UBS-2, respectively. Our results demonstrate that sulfonamides, even in small concentrations, significantly affect soil microbial population and respiration. Soil microbial respiration changes mediated by sulfonamides were dependent on length of exposure and concentration. It is recommended that antibiotics should be carefully watched and their impact on plant growth should be tested in the future studies.

Insight into soil nitrogen and phosphorus availability and agricultural sustainability by plant growth-promoting rhizobacteria.

Nitrogen and phosphorus are critical for the vegetation ecosystem and two of the most insufficient nutrients in the soil. In agriculture practice, many chemical fertilizers are being applied to soil to improve soil nutrients and yield. This farming procedure poses considerable environmental risks which affect agricultural sustainability. As robust soil microorganisms, plant growth-promoting rhizobacteria (PGPR) have emerged as an environmentally friendly way of maintaining and improving the soil's available nitrogen and phosphorus. As a special PGPR, rhizospheric diazotrophs can fix nitrogen in the rhizosphere and promote plant growth. However, the mechanisms and influences of rhizospheric nitrogen fixation (NF) are not well researched as symbiotic NF lacks summarizing. Phosphate-solubilizing bacteria (PSB) are important members of PGPR. They can dissolve both insoluble mineral and organic phosphate in soil and enhance the phosphorus uptake of plants. The application of PSB can significantly increase plant biomass and yield. Co-inoculating PSB with other PGPR shows better performance in plant growth promotion, and the mechanisms are more complicated. Here, we provide a comprehensive review of rhizospheric NF and phosphate solubilization by PGPR. Deeper genetic insights would provide a better understanding of the NF mechanisms of PGPR, and co-inoculation with rhizospheric diazotrophs and PSB strains would be a strategy in enhancing the sustainability of soil nutrients.

Uncovering the phytochemicals of root exudates and extracts of lead (Pb) tolerant Chrysopogon zizanioides (L.) Roberty in response to lead contamination and their effect on the chemotactic behavior of rhizospheric bacteria.

The chemical composition of root exudates and root extracts from Chrysopogon zizanioides (L.) Roberty cv KS-1 was determined in the presence of lead [Pb(II)]. Hitherto, no information is available in the literature concerning the phytochemical components of root exudates of C. zizanioides. Significantly higher concentrations of total carbohydrates (26.75 and 42.62% in root exudates and root extract, respectively), reducing sugars (21.46 and 56.11% in root exudates and root extract, respectively), total proteins (9.22 and 23.70% in root exudates and root extract, respectively), total phenolic acids (14.69 and 8.33% in root exudates and root extract, respectively), total flavonoids (14.30 and 12.28% in root exudates and root extract, respectively), and total alkaloids (12.48 and 7.96% in root exudates and root extract, respectively) were observed in samples from plants growing under Pb(II) stress in comparison to the respective controls. GC-MS profiling showed the presence of a diverse group of compounds in root exudates and extracts, including terpenes, alkaloids, flavonoids, carotenoids, plant hormones, carboxylic/organic acids, and fatty acids. Among the detected compounds, many have an important role in plant development, regulating rhizosphere microbiota and allelopathy. Furthermore, the results indicated that C. zizanioides exudates possess a chemotactic response for rhizospheric bacterial strains Bacillus licheniformis, Bacillus subtilis, and Acinetobacter junii Pb1.

Behavior of fluorescent Pseudomonas under different concentrations of heavy metals (Zn and Cu)

The use of chemical fertilizers has resulted in the depletion of soils in mineral elements and telluric microorganisms. Thus, for an improvement in crop growth, the exploitation of telluric microorganisms such as Pseudomonas can be an alternative. Laboratory work has made it possible to isolate strains of Pseudomonas from the rhizospheres of tomato, eggplant and onion. These strains were also tested in the presence of different concentrations of certain metals (CuSO4 and ZnSO4 (0, 1, 3, 4, 5 and 6 mmol/l). The tests carried out in the laboratory in the presence of Cu and Zn revealed a very significant reduction in the number of colonies of the strains of Pseudomonas for the concentrations of 5 and 6 mmol/l. The results showed better zinc tolerance for both tomato and onion rhizosphere strains. In the presence of Cu, the strain isolated from tomato rhizosphere shows more tolerance to heavy metals. These results made it possible to isolate different strains of Pseudomonas and to specify their tolerance thresholds for heavy metals.

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.

Plant growth-promoting bacteria improve Triticum aestivum L. growth and photosynthetic activity in sulfonamide-contaminated soil

Antibiotics are disseminated by grazing animals or their feces throughout agricultural areas. These antibiotics, as environmental pollutants, have a negative impact on plant growth and physiology. Sulfonamides are frequently used to protect livestock production, but they also have a considerable negative impact on plant growth and rhizospheric bacteria. Plants are sensitive to their surroundings, and they employ their internal biological systems to deal with the threats to their growth and development. Soil microbes, which are the most common inhabitants, have amazing metabolic capacities that enable them to overcome abiotic constraints. The effects of sulfonamide stress on wheat cultivar Chakwal-50 were studied in terms of morphological and biochemical processes, as well as stress mitigation by microorganisms isolated from wheat rhizospheric soil. This research looked at the effects of four new derived sulfonamides (SAs): 2-phenylsulfonyl hydrazine carbothioamide (TSBS-1), N,2-bis phenylhydrazine carbothioamide (TSBS-2), aminocarbonyl benzene sulfonamide (UBS-1), and N, N'-carboxyl dibenzene sulfonamide (UBS-2). Five rhizospheric bacterial strains were used: AC (Actinobacteria sp.), RS-3a (Bacillus sp.), RS-7a (Bacillus subtilis), RS-4a (Enterobacter sp.), and RS-5a (Enterobacter sp.). T. aestivum seeds were sterilized before being cultivated in soil polluted with various sulfonamide derivatives and inoculated with various bacterial strains under natural environmental conditions. To analyze the effect of sulfonamides on several aspects of plant growth, data from each antibiotic and bacterial strain was used to determine shoot fresh weight, root fresh weight, root and shoot length, number of leaves, and photosynthetic activity on the 15th day of germination. According to the results, Inoculation of Bacillus spp. (RS-3a) produced a maximum shoot fresh weight (FW) and shoot length by 8.14 g and 15.19 cm, respectively. Actinobacteria sp. (AC) had the highest chlorophyll value of 37 μg/g FW, while Bacillus spp. (RS-3a) increased carotenoid values with the average value of 550 μg/g FW by reducing sulfonamide stress. Following this preliminary screening, some bacterial strains were found to be promising plant growth promoting rhizobacteria for improving plant growth in a way that was both safe and effective.

Optimization of cultural conditions using response surface methodology and modeling of indole-3-acetic acid production by Saccharothrix texasensis MB15

This study aimed to develop a low-cost medium based on wheat waste (leaves and roots) to enhance Indole-3-Acetic Acid (IAA) production by the actinobacterial strain Saccharothrix texasensis MB15, using the Response Surface Methodology (RSM). Among eighteen endophytic or rhizospheric actinobacterial strains, Saccharothrix texasensis MB15 secreted high levels of IAA under standard cultural conditions. A Placket-Burman screening design was conducted to estimate the composition of low-cost medium and cultural conditions for S. texasensis MB15. Three factors, l-tryptophan, leaves extract, and inoculum quantity, respectively, showed a significant effect on IAA production by S. texasensis MB15. The RSM optimization step, for the three main factors, showed that improvement of IAA production was very significant, passing from 47 μg/ml within 120 h to more than 148 μg/ml within 96 h under RSM optimized conditions. From RSM analysis, the amounts of produced IAA were increased to an overall 2.65-fold in fermentation liquor, with a coefficient of determination R2 of 0.993, which indicates that 99.30% of the variability in the response can be accounted for by the model. This is the first paper reporting RSM-based medium optimization of IAA by S. texasensis MB15, isolated from the hypersaline soil in an arid region of Algeria, exploring organic wastes.

Rhizospheric PGPR Strains of Wheat, Barley and Trefoil Grown in Ağrı Province

The present study aimed to isolate potential plant growth rhizobacteria (PGPR) from various crops in agricultural areas in Ağrı-Turkey and their characterization. For this goal, rhizospheric soil samples of wheat, barley and trefoil were collected from 12 different locations in Ağrı province. Bacteria isolation studies were carried out with these rhizospheric samples. Then, to determine the PGPR properties of each isolate; nitrogen fixation, phosphate dissolution, siderophore, ammonia and HCN production tests were performed. Molecular identification of active isolates determined as suitable for development of biofertilizers, biostimulants and/or bioprotectants was done by PCR and sequencing applications performed with universal 16S rRNA primers. According to the results, 29 potential PGPR isolates were determined and their molecular characterization was done. These isolates were distributed in Arthrobacter, Bacillus, Brevibacterium, Enterobacter, Pantoea, Pseudomonas, Microbacterium and Stenotrophomonas according to their 16S rRNA sequence similarities.

Analysis of the Genome of the Heavy Metal Resistant and Hydrocarbon-Degrading Rhizospheric Pseudomonas qingdaonensis ZCR6 Strain and Assessment of Its Plant-Growth-Promoting Traits.

The Pseudomonas qingdaonensis ZCR6 strain, isolated from the rhizosphere of Zea mays growing in soil co-contaminated with hydrocarbons and heavy metals, was investigated for its plant growth promotion, hydrocarbon degradation, and heavy metal resistance. In vitro bioassays confirmed all of the abovementioned properties. ZCR6 was able to produce indole acetic acid (IAA), siderophores, and ammonia, solubilized Ca3(PO4)2, and showed surface active properties and activity of cellulase and very high activity of 1-aminocyclopropane-1-carboxylic acid deaminase (297 nmol α-ketobutyrate mg−1 h−1). The strain degraded petroleum hydrocarbons (76.52% of the initial hydrocarbon content was degraded) and was resistant to Cd, Zn, and Cu (minimal inhibitory concentrations reached 5, 15, and 10 mM metal, respectively). The genome of the ZCR6 strain consisted of 5,507,067 bp, and a total of 5055 genes were annotated, of which 4943 were protein-coding sequences. Annotation revealed the presence of genes associated with nitrogen fixation, phosphate solubilization, sulfur metabolism, siderophore biosynthesis and uptake, synthesis of IAA, ethylene modulation, heavy metal resistance, exopolysaccharide biosynthesis, and organic compound degradation. Complete characteristics of the ZCR6 strain showed its potential multiway properties for enhancing the phytoremediation of co-contaminated soils. To our knowledge, this is the first analysis of the biotechnological potential of the species P. qingdaonensis.

Evaluation of the anti-oomycete bioactivity of rhizosphere soil-borne isolates and the biocontrol of soybean root rot caused by Phytophthora sojae

Phytophthora sojae is an important pathogen that causes soybean root rot. In this study, 200 rhizosphere bacteria were isolated from soybean rhizosphere soil. Six rhizosphere strains that showed antagonistic activity against Phytophthora sojae, SN337-SN342, were screened with further confrontation experiments. The biocontrol activities of the 6 strains, especially SN337, were subsequently characterized and evaluated. In vitro experiments showed that SN337, as a newly developed biocontrol agent, had good antagonistic activity against Phytophthora sojae. In the evaluation of soybean growth promotion, a fermented broth of strain SN337 increased shoot height and root length by 13% and 37.5%, respectively, compared with a control. Importantly, the incidence caused by P. sojae decreased in soybean plants treated with SN337. The fermentation broth of strain SN337 also clearly disintegrated zoospores of P. sojae. The biocontrol effects were further investigated based on the changes in rhizosphere soil microorganisms before and after inoculation with pathogens. Compared to P. sojae infection without SN337 treatment, the abundance of bacteria, fungi, actinomycetes and total microbes were increased, whereas P. sojae was decreased in the rhizosphere of soybean infected by P. sojae inoculation with SN337 treatment. The results indicated that strain SN337 played a role in the maintenance of the soybean rhizosphere environment by increasing the proportion of beneficial microorganism in the soil. In this study, the biocontrol effects of strain SN337 were evaluated based on antagonistic activity and biocontrol assays and on soil microbial analysis. Our results provide new practical clues for developing fungicides for the sustainable management of soybean root rot caused by P. sojae.

ISOLATION OF BEAUVERIA BASSIANA (DEUTEROMYCOTINA: HYPHOMYCETES) FROM THE SOILS OF COFFEE FIELDS AND INSECTICIDE ACTIVITY AGAINST HYPOTHENEMUS HAMPEI (COLEOPTERA: SCOLYTIDAE)

ABSTRACT Coffee berry borer (CBB), Hypothenemus hampei (Ferrari) is one of the most important pests of coffee marketed in Cameroon and the world. This insect lives an endophytic life in the berries and remains very difficult to fight with the spraying of synthetic pesticides. This study aims at investigating the potential impact of two native strains of Beauveria bassiana (Balsamo) Vuillemen (Deuteromycotina: Hyphomycetes) from Cameroon against the CBB. B. bassiana strains were isolated from rhizosphere strains of coffee farms. The efficiency tests were conducted on adult H. hampei. Five treatments of B.bassiana were used compared with Pyriforce (Chlorpyriphos-ethyl). Results indicate that, the B. bassiana strains were different in terms of their macromorphological characteristics. They were virulent against the CBB irrespective of the mode of application of spores directly to the borer as well as to the berries. These results clearly showed that the two isolates of B. bassiana, native to coffee growing areas in Cameroon, can be used as potential biological control agents against H. hampei and as alternatives to chemical insecticides in integrated pest management programmes for coffee.

Rhizosphere competent Pseudomonas indoloxydans (F3-47) as a plant growth promoter and enhancer of Zea mays L. under greenhouse and field trials

A rhizospheric bacterium belonging to the genus Pseudomonas isolated from the rhizosphere of maize was evaluated for the plant growth promoting and biocontrol traits. The strain was subjected to the different PGP and biocontrol traits such as ammonia, IAA, siderophores, phosphate solubilisation, ACC deaminase, HCN production, cellulase, pectinase and chitinase activity. 16S rRNA sequencing showed maximum homology with the strain Pseudomonas indoloxydans IPL-1(NR115922). In vivo plant growth promotion assay with the strains on maize seedlings showed a significant increase in the biometric parameters with respect to the number of shoots (32%) and roots (27%) and its fresh weight (20%) and dry weight (54%). Different formulations of the strain tested in fields revealed that the maize plants treated with the talc and lignite formulations showed a considerable increase in the growth of maize when compared to the plants without any treatment. The study concluded that the rhizosphere strains Pseudomonas indoloxydans (F3- 47) could be a potential plant growth promoter for future exploration in agriculture.