Inhibition of Polyphosphate Degradation in Synechocystis sp. PCC6803 through Inactivation of the phoU Gene

Phosphorus is an essential but non-renewable nutrient resource critical for agriculture. Luxury phosphorus uptake allows microalgae to synthesize polyphosphate and accumulate phosphorus, but, depending on the strain of algae, polyphosphate may be degraded within 4 hours of accumulation. We studied the recovery of phosphorus from wastewater through luxury uptake by an engineered strain of Synechocystis sp. with inhibited polyphosphate degradation and the effect of this engineered Synechocystis biomass on lettuce growth. First, a strain (ΔphoU) lacking the phoU gene, which encodes a negative regulator of environmental phosphate concentrations, was generated to inhibit polyphosphate degradation in cells. Polyphosphate concentrations in the phoU knock-out strain were maintained for 24 h and then decreased slowly. In contrast, polyphosphate concentrations in the wild-type strain increased up to 4 h and then decreased rapidly. In addition, polyphosphate concentration in the phoU knockout strain cultured in semi-permeable membrane bioreactors with artificial wastewater medium was 2.5 times higher than that in the wild type and decreased to only 16% after 48 h. The biomass of lettuce treated with the phoU knockout strain (0.157 mg P/m2) was 38% higher than that of the lettuce treated with the control group. These results indicate that treating lettuce with this microalgal biomass can be beneficial to crop growth. These results suggest that the use of polyphosphate-accumulating microalgae as biofertilizers may alleviate the effects of a diminishing phosphorous supply. These findings can be used as a basis for additional genetic engineering to increase intracellular polyphosphate levels.

Rhizoglomus variabile and Nanoglomus plukenetiae, Native to Peru, Promote Coffee Growth in Western Amazonia

Coffee (Coffea arabica) is among the world's most economically important crops. Coffee was shown to be highly dependent on arbuscular mycorrhizal fungi (AMF) in traditionally managed coffee plantations in the tropics. The objective of this study was to assess AMF species richness in coffee plantations of four provinces in Perú, to isolate AMF isolates native to these provinces, and to test the effects of selected indigenous AMF strains on coffee growth. AMF species were identified by morphological tools on the genus level, and if possible further to the species level. Two native species, Rhizoglomus variabile and Nanoglomus plukenetiae, recently described from the Peruvian mountain ranges, were successfully cultured in the greenhouse on host plants. In two independent experiments, both species were assessed for their ability to colonize coffee seedlings and improve coffee growth over 135 days. A total of 35 AMF morphospecies were identified from 12 plantations. The two inoculated species effectively colonized coffee roots, which resulted in 3.0-8.6 times higher shoot, root and total biomass, when compared to the non-mycorrhizal controls. R. variabile was superior to N. plukenetiae in all measured parameters, increasing shoot, root, and total biomass dry weight by 4.7, 8.6 and 5.5 times, respectively. The dual inoculation of both species, however, did not further improve plant growth, when compared to single-species inoculations. The colonization of coffee by either R. variabile or N. plukenetiae strongly enhances coffee plant growth. R. variabile, in particular, offers enormous potential for improving coffee establishment and productivity. Assessment of further AMF species, including species from other AMF families should be considered for optimization of coffee growth promotion, both alone and in combination with R. variabile.

Improvement in Essential Oil Quantity and Quality of Thyme (Thymus vulgaris L.) by Integrative Application of Chitosan Nanoparticles and Arbuscular Mycorrhizal Fungi under Water Stress Conditions

Water stress is one of the critical abiotic stresses and limiting factors in the productivity of plants, especially in arid and semi-arid regions. In recent years, the application of bio-fertilizer and stress-modulating nanoparticles (NPs) is known as one of the eco-friendly strategies for improving plants quantity and quality under stressful conditions. In order to achieve the desirable essential oil (EO) quality and quantity of thyme in water deficit conditions, a 2-year field experiment was carried out as a split plot based on the randomized complete block design (RCBD), with 12 treatments and three replications. The treatments included different irrigation levels, containing irrigation at 80% field capacity (FC80) as no stress, 60% FC as moderate water stress (FC60) and 40% FC as severe water stress (FC40), as well as four different fertilizer sources, including non-application of fertilizer (control), application of arbuscular mycorrhizal fungi (AMF), chitosan NPs (CHT) and co-application of AMF+CHT NPs. The results demonstrated that the dry yield of thyme decreased by 13% and 40.3% under FC60 and FC40 water stress conditions. However, co-application of AMF+CHT NPs enhanced the dry yield of thyme by 21.7% in comparison to the control (non-application of fertilizer). The maximum EO content (2.03%) and EO yield (10.04 g 7 g m^-2) of thyme were obtained under moderate water stress (FC60) fertilized with AMF+CHT NPs. Co-application of AMF+CHT NPs enhanced the EO content and EO yield of thyme by 17.1% and 42.7%, respectively. Based on the GC-MS and GC-FID analysis, 38 constituents were identified in the thyme EO, with the major constituents being thymol (35.64-41.31%), p-cymene (16.35-19.38%), γ-terpinene (12.61-13.98%) and carvacrol (2.78-3.93%) respectively. The highest content of thymol and γ-terpinene was obtained under moderate water stress (FC60) fertilized with AMF+CHT NPs. In addition, the highest content of p-cymene and carvacrol was observed in the severe water stress (FC40) fertilized with AMF+CHT NPs. The present research suggests that the co-application of AMF+CHT NPs represents a sustainable and eco-friendly strategy for improving the EO quantity and quality of thyme under water stress conditions.

Kernel color and fertilization as factors of enhanced maize quality

Maize is an important staple crop and a significant source of various nutrients. We aimed to determine the macronutrients, antioxidants, and essential elements in maize genotypes (white, yellow, and red kernel) using three different fertilizers, which could be used as a basis to increase the nutrient density of maize. The fertilizer treatments used bio- and organic fertilizers as a sustainable approach, urea, as a commonly used mineral fertilizer, and the control (no fertilization). We evaluated the yield, concentration of macronutrient (protein, oil, and starch), nonenzymatic antioxidants (phenolics, yellow pigment, total glutathione (GSH), and phytic phosphorus), and reduction capacity of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, as well as essential elements that are commonly deficient in the diet (Mg, Ca, Fe, Mn, Zn, Cu, and S) and their relationships with phytic acid. The genotype expressed the strongest effect on the variability of grain yield and the analyzed grain constituents. The red-kernel hybrid showed the greatest accumulation of protein, oil, phenolics, and essential elements (Ca, Fe, Cu, and S) than a yellow and white hybrid, especially in the biofertilizer treatment. The yellow kernel had the highest concentrations of yellow pigment, GSH, phytic phosphorous, Mg, Mn, and Zn (19.61 µg g^-1, 1,134 nmol g^-1, 2.63 mg g^-1, 1,963 µg g^-1, 11.7 µg g^-1, and 33.9 µg g^-1, respectively). The white kernel had a greater starch concentration (2.5% higher than that in the red hybrid) and the potential bioavailability of essential metals, particularly under no fertilization. This supports the significance of white maize as a staple food in many traditional diets across the world. Urea was important for the enhancement of the antioxidant status (with 88.0% reduction capacity for the DPPH radical) and increased potential Zn bioavailability in the maize kernels (13.3% higher than that in the biofertilizer treatment). This study underlines the differences in the yield potential and chemical composition of red, yellow, and white-kernel maize and their importance as a necessary part of a sustainable human diet. This information can help determine the most appropriate genotype based on the antioxidants and/or essential elements targeted for kernel improvement.

Pseudomonas fluorescens NK4 siderophore promotes plant growth and biocontrol in cucumber

AIMS

To test the effect of zinc oxide nanoparticle (ZnO-NP) supplementation for enhancing the efficacy of Pseudomonas fluorescens NK4 siderophore as a biocontrol agent against Pseudomonas viridiflava NK2 and a plant growth promoter.

METHODS AND RESULTS

Cucumber seedlings were treated with a suspension of P. fluorescens NK4 and its siderophore generated in siderophore-inducing medium (SIM), SIM supplemented with ZnO-NP (<100 nm), and SIM supplemented with Zn²⁺ ions from Zn(NO₃ )₂ . Supplementing SIM with ZnO-NP increased siderophore secretion in P. fluorescens NK4, and irrigation of cucumber seedlings with a filtrate containing the ZnO-NP-supplemented siderophore increased survival, improved vegetative and root growth, and thus increased yield similar to the effects of dipping seedlings in a P. fluorescens NK4 suspension. Both P. fluorescens NK4 and its ZnO-NP-supplemented siderophore inhibited P. viridiflava NK2 population growth in planta.

CONCLUSIONS

The siderophore of P. fluorescens NK4 produced by ZnO-NP supplementation can be employed as a bio-control agent and bio-fertilizer.

SIGNIFICANCE AND IMPACT OF THE STUDY

ZnO-NPs can boost the synthesis of siderophores, which can then be employed as bio-fertilizers to boost iron bioavailability in iron-deficient soils.

[Effects of chemical fertilizer reduction combined with humic acid bio-fertilizer on soil biological properties and dry matter mass of maize.]

A reduction of chemical fertilizers and improving fertilizer utilization rate are important for ensuring a balance between plant growth and minimizing the degradation of the black soil. We conducted a 2-year pot experiment with four treatments during 2019 and 2020, including T₀: no fertilizer, T₁: conventional use of chemical fertilizer, T₂: 15% reduction of the chemical fertilizer combined with 400 kg·hm^-2 of humic acid bio-fertilizer (HABF), and T₃: 30% reduction of the chemical fertilizer combined with 600 kg·hm^-2 of HABF, to examine the effect of reduction rates of chemical fertilizers combined with the HABF on soil microbial abundance, enzyme activity and nutrient content in maize cultivation. The results showed that the application of HABF significantly increased the abundance of soil bacteria and fungi, with the number of microbial colonies being positively correlated with the amount of HABF. When measured at the tassel stage of maize growth, T₂ and T₃ treatments significantly increased the activities of urease, sucrase, and catalase in soil by 11.4%-21.6%, 34.9%-46.7%, and 6.5%-13.4%, respectively. The available nitrogen contents in T₂ and T₃ treatments were higher than that in the T₁ treatment by 8.2%-18.1%, which ensured the sufficient nitrogen supply to maize after the tassel stage. Soil available phosphorus and available potassium contents increased by 17.1%-121.0% and 9.6%-57.3%, respectively, compared with T₁ treatment. With the increases of the amount of HABF, the activation effects of soil phosphorus and potassium and dry matter mass per plant increased significantly in T₂ and T₃ treatments compared with T₁ treatment. In conclusion, HABF promoted the proliferation of soil bacteria and fungi, improved activities of catalase, urease, and sucrase, soil nutrient contents, and dry matter mass per plant. The 15% reduction of chemical fertilizer combined with 400 kg·hm^-2 of HABF is the most suitable nutrient management strategy for maize production in black soil.

Nocardia acididurans sp. nov., an acid-tolerant actinobacterium isolated from bio-fertilizer of Musa species

A novel acid-tolerant actinobacterium (strain LPG 2^T), which formed fragmented substrate mycelia, was isolated from bio-fertiliser of Musa spp. collected from Lampang Province, Thailand. Its morphological and chemotaxonomic properties, e.g., the presence of mycolic acid and MK-8 (H_4ω-cycl) in the cells, showed that strain LPG 2^T was a member of the genus Nocardia. 16S rRNA gene sequence analysis revealed that this strain was closely related to Nocardia otitidiscaviarum NBRC 14405^T (98.7 %). The low average nucleotide identity-blast and digital DNA-DNA hybridization values (<78.6 and <24.0 %, respectively), and several phenotypic differences between strain LPG 2^T and its related Nocardia type strains, indicated that the strain merits classification as representing a novel species of the genus Nocardia, for which we propose the name Nocardia acididurans sp. nov. The type strain is LPG 2^T (=TBRC 11242^T=NBRC 114293^T).

Isolation, Characterization, and Evaluation of Native Rhizobacterial Consortia Developed From the Rhizosphere of Rice Grown in Organic State Sikkim, India, and Their Effect on Plant Growth

Eight rhizospheric bacteria were isolated from the organic paddy fields of Sikkim, India, and identified as Pseudomonas kribbensis KSB, Burkholderia cenocepacia SRD, Kosakonia oryzendophytica YMA7, Pseudomonas rhodesiae SRB, Bacillus sp. ARA, Paenibacillus polymyxa COW3, Bacillus aryabhattai PSB2, and Bacillus megaterium PSB1. They showed plant growth-promoting attributes in rice and have bio-control potential against phytopathogen Colletotrichum gloeosporioides of large cardamom (Amomum subulatum). Burkholderia cenocepacia SRD showed production of indole acetic acid and ammonia and solubilization of phosphate and potassium and also possessed nitrogen fixation potential. It showed antagonistic activity against two other plant pathogens of large cardamom, viz., Curvularia eragrostidis and Pestalotiopsis sp., under in vitro conditions. The liquid bacterial consortium was prepared using the bacterial strains SRB, PSB1, and COW3 (Consortia-1); PSB2, SRD, and COW3 (Consortia-2); and COW3, KSB, and YMA7 (Consortia-3) to increase the growth and yield of rice plants under organic farming conditions. Greenhouse and field studies showed that the Consortia-3 had the highest plant growth-promoting activity. Consortia-3 demonstrated better agronomic performance in terms of root length (9.5 cm),number of leaflets per plant (5.3), grains per panicle (110.6), test grain weight (27.4 g), dry root weight per plant (0.73 g), and total dry biomass per plant (8.26 g).

Biofertilizer Activity of Azospirillum sp. B510 on the Rice Productivity in Ghana

Rice production in Ghana has become unsustainable due to the extremely nutrient-poor soils. It is caused by inadequate soil fertility management, including the inefficient application of fertilizers. A practical solution could be the biofertilizers, Azospirillum sp. B510. We performed field trials in Ghana and Japan to compare the effects of B510 colonization on selected Ghanaian rice varieties grown. The B510 inoculation significantly enhanced the rice cultivars’ growth and yield. The phenotypic characteristics observed in rice varieties Exbaika, Ex-Boako, AgraRice, and Amankwatia were mainly short length and high tillering capacity. These features are attributed to the host plant (cv. Nipponbare), from which the strain B510 was isolated. Furthermore, Azospirillum species has been identified as the dominant colonizing bacterium of rice rhizosphere across a diverse range of agroecologies in all major rice-growing regions in Ghana. Our results suggest that the utilization of B510 as a bio-fertilizer presents a promising way to improve rice growth, enhance soil fertility, and sustain rice productivity in Ghana.

Yarrowia lipolytica: a multitalented yeast species of ecological significance

Yarrowia lipolytica is characterized by GRAS (Generally regarded as safe) status, the versatile substrate utilization profile, rapid utilization rates, metabolic diversity and flexibility, the unique abilities to tolerate to extreme environments (acidic, alkaline, hypersaline, heavy metal-pollutions and others) and elevated biosynthesis and secreting capacities. These advantages of Y. lipolytica allow us to consider it as having great ecological significance. Unfortunately, there is still a paucity of relevant review data. This mini-review highlights ecological ubiquity of Y. lipolytica species, their ability to diversify and colonize specialized niches. Different Y. lipolytica strains, native and engineered, are beneficial in degrading many environmental pollutants causing serious ecological problems worldwide. In agriculture has a potential to be a bio-control agent by stimulating plant defense response, and an eco-friendly bio-fertilizer. Engineered strains of Y. lipolytica have become a very promising platform for eco-friendly production of biofuel, commodities, chemicals and secondary metabolites of plant origin, obtaining which by other method were limited or economically infeasible, or were accompanied by stringent environmental problems. Perspectives to use potential of Y. lipolytica's capacities for industrial scale production of valuable compounds in an eco-friendly manner are proposed.

[Effects of lime and ammonium carbonate fumigation coupled with bio-organic fertilizer application on banana fusarium wilt and bacterial community.]

Taking banana continuous planting soil with high banana fusarium wilt disease incidence as a test site, we examined the effect of lime and ammonium carbonate fumigation coupled with bio-organic fertilizer on the suppression of banana fusarium wilt disease and the structure and composition of bacterial community, using real-time quantitative PCR and high-throughput sequencing. The results showed that the disease incidence was reduced by 13.3% and 21.7% in the treatments of LAOF (lime and ammonium carbonate fumigation coupled with organic fertilizer) and LABF (lime and ammonium carbonate fumigation coupled with bio-organic fertilizer), respectively, compared with OF (application of organic fertilizer without fumigation), while the copy number of Fusarium was decreased by 22.4% and 33.0%, respectively. Compared with non-fumigation treatment, lime and ammonium fumigation coupled with different fertilizer applications significantly reduced bacteria richness and diversity, with different community structure, while fumigation had a decisive effect on bacterial community composition. Bacterial richness and diversity of LABF were lower than those of other treatments, while microbial community structure was clearly disparate from other treatments. Compared with non-fumigation treatment, the relative abundance of Mizugakiibacter, Brucella, and Rhodanobacter were significantly improved in the fumigation coupled with different fertilization treatments. Those three genera in LABF were higher than those in LAOF, with significant differences for the relative abundances of Mizugakiibacter and Brucella. Therefore, fumigation combined with bio-organic fertilizer application could reduce the copy number of pathogen, alter soil bacterial community structure and stimulate beneficial bacteria in the resident soil, and thus reduce the occurrence of banana fusarium wilt.

A Universally Primed-Polymerase Chain Reaction (UP-PCR) Marker to Discriminate Clonostachys rosea ACM941 from Related Strains

Clonostachys rosea strain ACM941 is an effective biocontrol agent against several crop diseases including Fusarium head blight. In anticipation of its increased relevance going forward, the development of a reliable DNA-based molecular marker to track it is essential. Universally primed-PCR (UP-PCR) has been used successfully to differentiate other C. rosea strains. Herein, the development of a UP-PCR marker for ACM941 is described. A combination of two primers (AS15 and L45) produced a ~450 bp fragment that was unique to ACM941 compared to other commercial biocontrol agents. Primers subsequently designed based on the obtained fragment also produced a similarly unique band from ACM941 alone. BLAST analysis of the amplified sequence did not yield any homologous sequence in available online databases or within the closely related C. rosea IK726 and CBS125111 strains’ genomes. The specificity of this marker for ACM941 was validated against ten additional C. rosea strains isolated from Canada, with ACM941 producing the brightest band. Taken together, these results imply that the UP-PCR primers AS15 and L45 and the amplified fragment can be used to detect and monitor the ACM941 strain after its release into the environment.

Vermicompost Supply Modifies Chemical Composition and Improves Nutritive and Medicinal Properties of Date Palm Fruits From Saudi Arabia

To meet the increased demand for phytochemicals, plant cultivation in soil amended with biofertilizers has been developed. Here, we aimed to use vermicompost as an environmentally safe biofertilizer to enhance the nutritive and medicinal value of five common cultivars of Saudi date palm; namely Phoenix dactylifera L. var. Ajwa, Hulwa, Ruthana, Sefri, and Luban. To determine changes in the fruit nutritive composition, primary metabolites, antioxidants, phenolic compounds and mineral profiles were analyzed in the fruits from non-fertilized and vermicompost-fertilized date palms. We also tested how changes in the fruit chemical compositions due to vermicompost fertilization affected their medicinal potentials. Applying vermicomposts generally increased primary metabolites, vitamins, and mineral content as well as the medicinal potential of the date palm fruits. This positive effect is possibly explained by the role of vermicomposts in improving soil health and fertility. Furthermore, clustering analyses and principal component analysis (PCA) indicated cultivar-specific responses. PCA analysis also revealed that the bioactivities of the date palm fruit extracts and their antioxidants tended to display correlated output values. One of the highly accumulated phenolic compounds, β-D-glucogallin, was extracted and purified from P. dactylifera L. var. Ajwa fruits and showed significant antioxidant, anticancer, antibacterial, antimutagenic, and antiprotozoal activities. Overall, applying vermicompost is an innovative approach to increase the nutritive quality and medicinal potential of date palm fruits.

Research progress in arbuscular mycorrhizal technology

Arbuscular mycorrhizal (AM) symbiosis facilitates plant mineral nutrient acquisition and plays key roles in plant adaptation to environmental stresses. The application of AM fungi is a component of sustainable agriculture and ecological restoration. We introduced the current status of AM fungi collections, production of commercial inocula and AM fungi related patents, summarized the research advances in inoculum production, inoculation techniques, and factors influencing the success of inoculation practice in the field, based on case studies of mycorrhizal technology in agriculture, horticulture, and ecological restoration. Finally, we proposed some basic scientific questions and technical bottleneck that deserve futher studies, to promote the development and application of mycorrhizal technologies.

Unexpected results in Chernozem soil respiration while measuring the effect of a bio-fertilizer on soil microbial activity

The number of studies investigating the effect of bio-fertilizers is increasing because of their importance in sustainable agriculture and environmental quality. In our experiments, we measured the effect of different fertilizers on soil respiration. In the present study, we were looking for the cause of unexpected changes in CO2 values while examining Chernozem soil samples. We concluded that CO2 oxidizing microbes or methanotrophs may be present in the soil that periodically consume CO2 . This is unusual for a sample taken from the upper layer of well-ventilated Chernozem soil with optimal moisture content.

Beneficial Soil Bacterium Pseudomonas frederiksbergensis OS261 Augments Salt Tolerance and Promotes Red Pepper Plant Growth

Soil salinity, being a part of natural ecosystems, is an increasing problem in agricultural soils throughout the world. Pseudomonas frederiksbergensis OS261 has already been proved to be an effective bio-inoculant for enhancing cold stress tolerance in plants, however, its effect on salt stress tolerance is unknown. The main aim of the present study was to elucidate P. frederiksbergensis OS261 mediated salt stress tolerance in red pepper. The plants were exposed to a salt stress using NaCl at the concentrations of 50, 100, and 150 mM after 12 days of transplantation, while plant growth and enzyme activity were estimated 50 days after sowing. The height in P. frederiksbergensis OS261 inoculated plants was significantly increased by 19.05, 34.35, 57.25, and 61.07% compared to un-inoculated controls at 0, 50, 100, and 150 mM of NaCl concentrations, respectively, under greenhouse conditions. The dry biomass of the plants increased by 31.97, 37.47, 62.67, and 67.84% under 0, 50, 100, and 150 mM of NaCl concentrations, respectively. A high emission of ethylene was observed in un-inoculated red pepper plants under salinity stress. P. frederiksbergensis OS261 inoculation significantly reduced ethylene emission by 20.03, 18.01, and 20.07% at 50, 100, and 150 mM of NaCl concentrations, respectively. Furthermore, the activity of antioxidant enzymes (ascorbate peroxidase, superoxide dismutase, and catalase) also varied in the inoculated red pepper plants. Salt stress resistance in the bacterized plants was evident from the improved antioxidant activity in leaf tissues and the decreased hydrogen ion concentration. Thus, we conclude that P. frederiksbergensis OS261 possesses stress mitigating property which can enhance plant growth under high soil salinity by reducing the emission of ethylene and regulating antioxidant enzymes.