Non-inoculated Soil Research Articles

First report of basal rot of yellow dragon fruit (Selenicereus megalanthus) caused by Fusarium oxysporum in Peru.

Cultivation of yellow dragon fruit (Selenicereus megalanthus) in Peru has recently expanded (Verona-Ruiz et al. 2020). In August 2021, approximately 170 of 1,110 dragon fruit cuttings (15.3%) in the university's nursery (6°26'10'' S; 77°31'25'' W) showed basal rot symptoms. Initial symptoms included small brown spots on the base of stems, expanding towards the top that became soft and watery. All symptomatic plants eventually died, i.e., a severity of 100%. The disease was more prevalent on cuttings during the rooting phase than on well-established cuttings. We collected five symptomatic cuttings from throughout the nursery. Four sections of 1 × 1 cm2 of tissue adjacent to the diseased area were excised from each cutting, immersed for 1 min in 2% NaClO, rinsed twice with sterile distilled water, placed on potato dextrose agar (PDA) medium (four sections per Petri plate, five plates), and incubated at 25°C for 7 days. Morphologically similar mycelia grew from all sections, and five monosporic isolates were obtained, one per plate. Colonies grew fast, reaching 60 to 64 mm in 7 days, and produced violet-white cottony aerial mycelia with orange sporodochia on PDA, and abundant macro- and microconidia on synthetic nutrient-poor agar. Macroconidia were straight to slightly curved, typically with 2 to 3 septa, 16.6 to 23.3 × 1.7 to 3.7 µm (n = 30); microconidia were oval or kidney-shaped, and commonly hyaline, 6.7 to 16.4 × 2.5 to 4.7 µm (n = 40). Genomic DNA was extracted from isolate AFHP-100, then the ITS region and the TEF1 and RPB2 partial genes were amplified and sequenced (Accession numbers PP977433, OR437358, PP537149) following Gardes and Bruns (1993) and O'Donnell et al. (1998). We conducted a BLASTn search of ITS sequence against the NCBI "nr" database and local 'megablast' searches of TEF1 and RPB2 sequences against FUSARIUM-ID v.3.0 (Torres-Cruz et al. 2022). We found 100%, 98.19 to 99.84%, and 98.81 to 99.76% identities in ITS, TEF1, and RPB2 sequences, respectively, to the ex-epitype and other reference strains of Fusarium oxysporum (CBS 144134, NRRL26406, among others). A maximum likelihood phylogenetic analysis with a TEF1-RPB2 concatenated dataset with FUSARIUM-ID sequences also showed isolate AFHP-100 was F. oxysporum. A pathogenicity test was carried out by inoculating wounded healthy roots of three cuttings with submersion in a 5 × 106 conidia/ml suspension for 25 min. Then, the inoculated plants were planted in sterile soil. One cutting with wounded roots submerged in sterile water served as a control. In parallel, sterile soil was inoculated with 20 mL of the conidial suspension, and another three healthy cuttings were planted. A cutting planted in noninoculated soil also served as a control. Basal rot symptoms developed in all inoculated plants after 25 days. After re-isolation, the same fungus, corroborated based on micromorphology and TEF1 sequence (PP335689), was recovered, fulfilling Koch's postulates. The isolate was deposited in the KUELAP Herbarium (voucher KUELAP-3214), located and administered by the National University Toribio Rodriguez de Mendoza de Amazonas, in Chachapoyas, Peru. Fusarium oxysporum has been reported to cause basal stem rot in Bangladesh and Argentina (Mahmud et al. 2021; Wright et al. 2007), and stem blight in Malaysia (Mohd Hafifi et al. 2019) on dragon fruit. This is the first report of F. oxysporum causing basal rot in S. megalanthus in Peru. This fungus is among the most destructive plant pathogens, and the rapid expansion of the crop in Peru requires a comprehensive knowledge of the biotic factors influencing production. Therefore, this report is foundational to implementing proper control strategies.

Cyanobacteria-based soil amendments in the soil-plant system: Effects of inoculations on soil nutrient and microbial dynamics under spring wheat growth

Cyanobacteria are promising alternatives to chemical fertilizers for managing nutrients and preserving soil function. In this study, two pot experiments were conducted to evaluate the effects of inoculations with the cyanobacterium Anabaena cylindrica on an arable Mollisol from the U.S. Upper Midwest and growth of spring wheat. Experiment 1 evaluated surface soil nutrient and microbial dynamics at early stages of wheat development. Experiment 2 evaluated the potential of microalgal inoculations (A. cylindrica and/or Chlamydomonas sp.) to replace urea and measured plant growth and soil parameters at three depths at harvest. Experiment 1 revealed inoculation increased surface soil soluble organic carbon (SolC), microbial biomass carbon (C), total nitrogen (N), mineral N, available phosphorus (P), and microbial activity. At day 42 after sowing, wheat plant N was higher in inoculated than non-inoculated soil, and the nitrate/nitrite level in inoculated soil significantly decreased in the presence of plants. In Experiment 2, inoculation had greater effects on surface soil than deeper soil depths for SolC, microbial biomass C and N, mineral N, and available-P. Grain yield was not statistically different in treatments with 100 % N from urea, 75 % N from A. cylindrica plus 25 % N-urea, and 100 % N from an algal mixture. Equivalent grain protein was achieved only when 25 % N from urea was replaced with N from A. cylindrica, highlighting the need for optimizing inoculation timing and plant N uptake. These results support the beneficial role of cyanobacteria-based inoculations for soil quality and plant growth, and as renewable resources for agricultural systems.

Reduced Antibiotic Resistance in the Rhizosphere of Lupinus albus in Mercury-Contaminated Soil Mediated by the Addition of PGPB.

The emergence of antibiotic resistance (AR) poses a threat to the "One Health" approach. Likewise, mercury (Hg) pollution is a serious environmental and public health problem. Its ability to biomagnify through trophic levels induces numerous pathologies in humans. As well, it is known that Hg-resistance genes and AR genes are co-selected. The use of plant-growth-promoting bacteria (PGPB) can improve plant adaptation, decontamination of toxic compounds and control of AR dispersal. The cenoantibiogram, a technique that allows estimating the minimum inhibitory concentration (MIC) of a microbial community, has been postulated as a tool to effectively evaluate the evolution of a soil. The present study uses the metagenomics of 16S rRNA gene amplicons to understand the distribution of the microbial soil community prior to bacterial inoculation, and the cenoantibiogram technique to evaluate the ability of four PGPB and their consortia to minimize antibiotic resistance in the rhizosphere of Lupinus albus var. Orden Dorado grown in Hg-contaminated soils. Results showed that the addition of A1 strain (Brevibacterium frigoritolerans) and its consortia with A2, B1 and B2 strains reduced the edaphic community´s MIC against cephalosporins, ertapenem and tigecycline. The metagenomic study revealed that the high MIC of non-inoculated soils could be explained by the bacteria which belong to the detected taxa,. showing a high prevalence of Proteobacteria, Cyanobacteria and Actinobacteria.

Inoculation Effect of Methanotrophs on Rhizoremediation Performance and Methane Emission in Diesel-Contaminated Soil.

During the rhizoremediation of diesel-contaminated soil, methane (CH4), a representative greenhouse gas, is emitted as a result of anaerobic metabolism of diesel. The application of methantrophs is one of solutions for the mitigation CH4 emissions during the rhizoremediation of diesel-contaminated soil. In this study, CH4-oxidizing rhizobacteria, Methylocystis sp. JHTF4 and Methyloversatilis sp. JHM8, were isolated from rhizosphere soils of tall fescue and maize, respectively. The maximum CH4 oxidation rates for the strains JHTF4 and JHM8 were 65.8 and 33.8 mmol·g-DCW-1·h-1, respectively. The isolates JHTF4 and JHM8 couldn't degrade diesel. The inoculation of the isolate JHTF4 or JHM8 significantly enhanced diesel removal during rhizoremediation of diesel-contaminated soil planted with maize for 63 days. Diesel removal in the tall fescue-planting soil was enhanced by inoculating the isolates until 50 days, while there was no significant difference in removal efficiency regardless of inoculation at day 63. In both the maize and tall fescue planting soils, the CH4 oxidation potentials of the inoculated soils were significantly higher than the potentials of the non-inoculated soils. In addition, the gene copy numbers of pmoA, responsible for CH4 oxidation, in the inoculated soils were significantly higher than those in the non-inoculated soils. The gene copy numbers ratio of pmoA to 16S rDNA (the ratio of methanotrophs to total bacteria) in soil increased during rhizoremediation. These results indicate that the inoculation of Methylocystis sp. JHTF4 and Methyloversatilis sp. JHM8, is a promising strategy to minimize CH4 emissions during the rhizoremediation of diesel-contaminated soil using maize or tall fescue.

Pseudomonas aeruginosa and Bacillus cereus Isolated from Brazilian Cerrado Soil Act as Phosphate-Solubilizing Bacteria

The phosphate-solubilizing microorganism is essential for soil quality and plant development and can serve as an alternative to reduce such Brazilian needs for importing phosphate overseas. Here, we isolated and selected bacteria from Brazilian Cerrado soils capable of solubilize phosphate. We obtained 53 bacteria isolates, of which 23 could solubilize phosphate at a pH of 7.0, 17 could solubilize phosphate at a pH of 6.0, and 8 could solubilize at a pH of 5.5. Using 16S rRNA gene sequences, we identified nine bacteria species clustered in four groups: Bacillus sp., Pseudomonas sp., Priestia sp., and Klebsiella sp. Our results revealed that the UFT01 (P. aeruginosa) and UFT42 (B. cereus) isolates exhibited the best phosphate solubilization performance at all tested pH values. We further recorded higher levels of solubilization and phosphate availability six days after the soil inoculation with P. aeruginosa, and enzymatic analysis of the soil samples revealed that the P. aeruginosa-inoculated samples resulted in four-fold higher enzymatic activities when compared to non-inoculated soils. The B. cereus soil inoculation increased β-glucosidase activities and resulted in reduced the activities of arylsulfatase. Altogether, our findings demonstrated that P. aeruginosa and B. cereus isolated from Cerrado soils showed high phosphate solubilization potential.

Identification and Characterisation of the Salt Tolerant Phosphate-Solubilising Bacterial Isolates for Enhancing Soil Fertility

In this study, 13 bacteria were isolated from the agricultural soils of Kyaukse city, Myanmar, and out of these isolates, two bacteria isolates viz. JU-24 and JU-33 are found to be potent phosphate (P) solubilisers and are selected for further studies. These two isolates are identified as Bacillus megaterium based on the 16S rRNA gene sequence. When the growth rates of these two isolates were tested for salt tolerance, they could grow well in media with NaCl concentrations of 3%, 6% and 9%. For 0% and 3% NaCl concentrations, JU-33 (84.37 mg/L for 0% NaCl and 130.36 mg/L for 3% NaCl) showed higher P-solubilising efficiency than JU-24 (73.29 mg/L for 0% NaCl and 87.42 mg/L for 3% NaCl) for both NaCl concentrations when inoculated in Ca3(PO4)2 containing liquid medium. In media containing AlPO4 and FePO4 without NaCl, the P-solubilising activity of JU-24 is higher than JU-33 for these two substrates. Moreover, these strains showed noticeable levels of P solubilisation activity in the presence of various carbon sources indicating high P-solubilising efficacy. The soil inoculation experiment revealed that inoculating the experimental soil with JU-33 resulted in an obvious increase in available P, which increased from 13.08 mg/L in the non-inoculated soil to 18.40 mg/L in the inoculated soil with the bacterial isolate, JU-33. This study clearly showed that JU-24 and JU-33 isolates could be used as biofertilizers in ecological agricultural systems and may help to sustain environmental health and soil productivity. The use of biofertilizers can reduce the use of expensive chemical fertilisers, reducing planting costs and improving soil fertility through long-term use. Biofertilizers can help solve the problem of feeding an increasing global population at a time when agriculture is facing various environmental stresses and are affordable for low-income farmers.

Cover crop usage for the sustainable management of soilborne diseases in woody ornamental nursery production system

Cover crops represent a potential tool for suppression of soil borne diseases in woody ornamental nursery production, which can cause significant economic losses. Field experiments were conducted in 2019 and 2020 to explore the effects of a cover crop and the timing of cover crop disturbance on soilborne disease suppression. Soils from red maple (Acer rubrum ‘October Glory’) plantations grown with or without a cover crop [crimson clover (Trifolium incarnatum)] were sampled following senescence of the cover crop. Greenhouse bioassays were conducted using red maple cuttings on inoculated (with Rhizoctonia solani, Phytopythium vexans or Phytophthora nicotianae) and non-inoculated field soils. Plant height, total and root fresh weight were measured, and the roots were assessed for disease severity on a 0 to 100% root damage scale. Pathogen recovery was assessed by culturing root pieces (~1 cm length) on oomycetes or Rhizoctonia semi-selective media. Soil samples were analyzed for organic matter, nitrogen, phosphorus, potassium, pH and Pseudomonad population count. A minimal effect of cover crop disturbance timing (late fall or early spring) was found on disease suppression. Cover crop usage reduced disease severity and pathogen recovery in red maple field soils. Plants grown in cover cropped soil had greater total, root and aboveground fresh weight compared with those from non-cover cropped soil, but plant height was not affected. Cover crops increased soil organic matter and total nitrogen in 2020. Pseudomonad populations were higher when cover crops were used. The results suggest that cover crops can reduce soilborne disease in woody ornamentals.

Selection and control efficiency of Trichoderma isolates against Fusarium oxysporum f. sp. ciceris in Iran

The antagonistic potential of forty isolates of Trichoderma spp. obtained from major chickpea growing areas in western part of Iran, were evaluated against Fusarium oxysporum f. sp. ciceris, the most important soil-born pathogen of chickpea. Among those, six species of Trichoderma harzianum, T. longibrachiatum, T. pleurotum, T. crassum, T. guizhouense,and Trichoderma sp. were identified based on morphological, molecular and phylogenetic analysis of concatenated DNA sequences of tef1 and rpb2 genes. All isolates were tested in vitro using dual culture method for their inhibition of the mycelial growth of the pathogen. Eight most antagonistic isolates, which suppressed colony growth of pathogen by 61.1–65.5%, were tested in vitro for production of volatile metabolites. All eight selected isolates produced volatile metabolites which prevented radial growth of pathogen from 17.5% to 31.0%. Antagonistic isolates provided significant protection against pathogen when mixed with soil or treated on seeds. Wilt control efficiency was greater for T. longibrachiatum KT8 (64.4%), T. harzianum KT9 (66.1%), and KT10 (69.5%) after 60 days of sowing highly susceptible chickpea cultivar JG-62 in inoculated soils. Greater wilt control efficiencies were detected for seed treatments with KT8 (69.1%), KT9 (72.7%), and KT10 (74.5%) isolates. Higher plant height, dry weight of root and shoot were recorded with these three superior isolates in seed treatments, inoculated and non-inoculated soils. Such superior isolates could be considered as promising antagonistic agents in biocontrol of chickpea Fusarium wilt for future studies. To the best of our knowledge, T. pleurotum and T. guizhouense are reported for the first time from Iran.

Impact of Inoculation with Pseudomonas aestus CMAA 1215T on the Non-target Resident Bacterial Community in a Saline Rhizosphere Soil.

Plant growth reduction caused by osmotic stress, pathogens, and nutrient scarcity can be overcome by inoculation with plant growth-promoting rhizobacteria (PGPR). Knowing the effects of PGPR on the microbial community beyond those on plant growth can bring new options of soil microbiota management. The present study aimed to investigate the effect of inoculation with the newly described Pseudomonas aestus CMAA 1215T [a 1-aminocyclopropane-1-carboxylate (ACC) deaminase and glycine-betaine producer] on the rhizosphere bacterial community of Zea mays in natural (non-salinized) and saline soil. The bacterial community structure was assessed by sequencing the V6-V7 16S ribosomal RNA using the Ion Personal Genome Machine™. The non-metric multidimensional scaling (NMDS) of the OTU profile (ANOSIM P < 0.01) distinguishes all the treatments (with and without inoculation under saline and natural soils). Inoculated samples shared 1234 OTUs with non-inoculated soil. The most abundant classes in all samples were Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Acidobacteriia, Bacteroidia, Thermoleophilia, Verrucomicrobiae, Ktenodobacteria, and Bacilli. The inoculation, on the other hand, caused an increase in the abundance of the genera Bacillus, Bryobacter, Bradyrhizobium, "Candidatus Xiphinematobacter", and "Candidatus Udaeobacter" independent of soil salinization. "Candidatus Udaeobacter" has the largest Mean Decrease in Gini Values with higher abundance on inoculated salted soil. In addition, Pseudomonas inoculation reduced the abundance of Gammaproteobacteria and Phycisphaerae. Understanding how inoculation modifies the bacterial community is essential to manage the rhizospheric microbiome to create a multi-inoculant approach and to understand its effects on ecological function.

Cover Crop Selection by Jointly Optimizing Biomass Productivity, Biological Nitrogen Fixation, and Transpiration Efficiency: Application to Two Crotalaria Species

Crotalaria spectabilis and Crotalaria juncea are cover crops (CC) that are used in many different regions. Among the main attributes of these species are their high potential for biomass production and biological fixation of nitrogen (BNF). Attempting to maximize these attributes, while minimizing water consumption through high transpiration efficiency (TE), is a challenge in the design of sustainable agricultural rotations. In this study, the relationship between biomass productivity, BNF, and TE in C. spectabilis and C. juncea was evaluated. For this purpose, an experiment was carried out under controlled conditions without water limitations and using non-inoculated soil. BNF was determined by the natural abundance of 15N, while TE was estimated by several different methods, such as gravimetric or isotopic method (13C). C. juncea produced 42% less dry matter, fixed 28% less nitrogen from the air, and had 20% less TE than C. spectabilis. TE results in both species were consistent across methodologies. Under simulated environmental conditions of high temperature and non-limiting soil water content, C. spectabilis was a relatively more promising species than C. juncea to be used as CC.

Assessment of methyl 2-({[(4,6-dimethoxypyrimidin-2-yl)carbamoyl] sulfamoyl}methyl)benzoate through biotic and abiotic degradation modes

AbstractDetoxification and management of environmental contaminants is an exigent issue of current times. Sulfonylurea herbicide, Bensulfuron-methyl was investigated for its degradation demeanour in soils, through biotic and abiotic modes (biodegradation and hydrolysis). Solid-liquid extraction of the herbicide was followed by GC-MS and UV-visible spectrophotometry analysis. The main metabolites observed were pyrimidinamine [149 m/z] and benzylsulfonamide [182 m/z]. The rate of biodegradation achieved by Aspergillus niger and Penicillium chrysogenum was 95% and 71%, respectively. The maximal decline in Bensulfuron-methyl concentration through hydrolysis was 48%. Furthermore, hydrolytic elimination was also evaluated based on time and pH. Both these parameters had a strong influence on the rate of transformation. Soils with lower pH exhibited an increased rate of degradation while a temperature of 27±2°C gave ideal conditions for herbicide decomposition. Percentage degradation and rate constant (k) followed first order reaction kinetics. Non-inoculated soils displayed less amounts of degradation. Furthermore, relative standard deviations were calculated for the residuals extracted in all soils. Analysis of variance (ANOVA) provided a p value &lt; 0.05 for both strains with R2 closer to 1 signifying the significance of the results. Both fungal strains proved their potential for Bensulfuron-methyl remediation in soils.

Growth promotion of apple plants is the net effect of binucleate Rhizoctonia sp. as rhizosphere-colonizing fungus

The functional relationship between binucleate Rhizoctonia sp. (BnRhizoctonia) and apple was investigated. Apple rootstock plantlets (Malling 9) were grown in BnRhizoctonia inoculated and non-inoculated soil after preliminary treatment with gamma-rays. A growth assay was performed in phytotron under two soil-water content regimes: an optimal one for plant growth and another inducing periodic plant water stress. At the end of the growth test, plant growth as fresh and dry weight of biomass produced over the trial period and fungal root colonization with culture-based methodology were estimated. Relative quantification of Rhizoctonia and soil fungi DNA using specific primers was performed. Overall, BnRhizoctonia inoculation gave a mean plant growth increase which accounted for 50% as compared to non-inoculated treatments. Although root colonization frequency did not differ between inoculated and uninoculated plants, the inoculated were highly colonised by BnRhizoctonia, whilst the others were colonized by a series of ascomycetes such as Fusarium spp., Alternaria sp. which quickly recolonized soil after preliminary soil treatment with gamma-rays acting soil microbial restoration. Water stress overall reduced plant growth; however, inoculation with BnRhizoctonia reduced this negative effect by about 30%. Findings of this study indicate that BnRhizoctonia acts as growth promoter; but this beneficial effect depends on its degree of root colonization and is affected by environmental interaction.

Phytoremediation of Oil-Contaminated Soils by Combining Flowering Plant Cultivation and Inoculation with &amp;lt;i&amp;gt;Acinetobacter junii&amp;lt;/i&amp;gt; Strain M-2

Oil contamination of the soil by petroleum products has become an enormous environmental problem. In this study, we examined whether remediation of oil-contaminated soils by cultivating three flowering plants (Mimosa, Gazania, and Zinnia) could be enhanced by inoculation with Acinetobacter junii strain M-2 at different plant growth stages (at sowing, at early growth, and at mid-growth). The growth of Zinnia cultivated in oil-contaminated soils inoculated at sowing was significantly superior to that in the non-inoculated soil. Although total petroleum hydrocarbon concentrations in soils inoculated at sowing were nominally lower than those in non-inoculated soils, especially in the case of Zinnia planting, the effect did not reach statistical significance. However, dehydrogenase activity was significantly higher in the soils inoculated with A. junii strain M-2 than in non-inoculated soils for all three plant species tested. These results demonstrate that a combination of ornamental plant cultivation (particularly Zinnia) and inoculation with A. junii strain M-2 increases the efficiency of oil-contaminated soil phytoremediation.

Application to soil of disinfectants through irrigation reduces Verticillium dahliae in the soil and verticillium wilt of olive

The application of disinfectants through drip irrigation could be a feasible practice against verticillium wilt (Verticillium dahliae) of olive. OX‐VIRIN (activated peroxide) and OX‐AGUA AL25 (quaternary ammonium compounds) are two disinfectants that have shown efficacy against V. dahliae in irrigation water and potential for reducing the disease in young olive plants. In this work, various post‐planting application strategies incorporating OX‐VIRIN (once a month, or twice a month on alternate or successive weeks) or OX‐AGUA AL25 (once a month, or twice a month on alternate weeks) were assessed for their effect on V. dahliae in soil, disease in olive trees, and olive yield, in a 2‐year pot‐experiment under natural environmental conditions. The disinfectants were injected via metering pumps into a drip irrigation system that irrigated olive trees planted in V. dahliae‐inoculated soil. All the application strategies significantly reduced the total inoculum density in soil compared to controls with no disinfectants and noninoculated soil. The microsclerotia density was also significantly reduced in disinfested soils by 73.6–86.8%, depending on the strategy. The symptoms and infection incidence were always lower in treatments subjected to disinfestation. The treatment with OX‐AGUA AL25 applied twice a month on alternate weeks most reduced the symptoms (by 53.0%) and colonization index (by 70.8%) with respect to untreated water control. This soil disinfestation also significantly strengthened the symptom remission. Tree growth and production were negatively affected by soil inoculation (reduced by 45.6% and 88.7%, respectively), but not so by disinfectants, which even relieved the reduction in inoculated soils, especially when OX‐AGUA AL25 was applied.

Impact of Cover Crop Usage on Soilborne Diseases in Field Nursery Production

Soilborne pathogens are a significant economic problem for nursery production in the Southeastern United States. The goal of this study was to determine the impact of cover crops on soilborne disease suppressiveness in such systems. Soils from red maple (Acer rubrum L.) plantation fields grown with and without cover crops were sampled, either while the cover crops were growing (pre-disked) or post-season, following cover crop incorporation into the soil (post-disked). Greenhouse bioassays were conducted using red maple seeds on inoculated (with Rhizoctonia solani (J.G. Kühn) or Phytophthora nicotianae (Breda de Haan)) and non-inoculated field soils. The damping-off, root rot disease severity, percent recovery of Rhizoctonia and Phytophthora, and pseudomonad population were examined during the two years of the experiment. Results showed that cover crop incorporation was beneficial for inducing disease supressiveness characteristics of soil. Cover crop incorporation into the soil significantly or numerically reduced disease severity and pathogen recovery in infested soil compared to the bare soil treatment. Cover crop incorporation was found to be partially associated with the reduction of seedling damping-off. The pseudomonad microbial population was greater when cover crop was present, and is thought to be antagonist to soilborne pathogens. Therefore, cover crops can be integrated in field nursery production systems to suppress soilborne pathogens.

The nematicidal potentiality of some algal extracts and their role in enhancement the tomato defense genes against root knot - nematodes

The nematicidal effect of three marine algal, Ulva fasciata Delile (UF) (green algae), Corallina mediterranea, Corallina officinalis (red algae), extracts on egg hatching and second-stage juveniles (J2) mortality of root-knot nematode (Meloidogyne incognita) in vitro compared to the nematicide activity of Oxamyl 24% SL (5 ml/l) was investigated. Results revealed that all treatments at the applied concentrations suppressed the egg hatching in 3 days. In details, the algal strain Ulva fasciata Delile extract showed the highest activity in decreasing the eggs hatchability after 3 days with 87%. Consequently, all treatments significantly increased the mortality of J2 larvae after 12, 24, and 48 h compared to the control treated with distilled water. Under greenhouse conditions, all treatments in inoculated soils cultivated with tomato plants had reduced numbers of galls, egg-masses/plant, and the number of J2/250 g than the non-inoculated soil. The algal extract and the Oxamyl 24% SL (5 ml/l) increased the length and fresh weight of plant shoots and roots than the untreated. However, there were no differences in shoots and roots fresh weights and their lengths in the plant treated with Oxamyl 24% SL (5 ml/l) or the extracts of U. fasciata and Corallina officinalis. These results were closely similar to control. Both of peroxidase and polyphenol enzymes activity for the control plants remained relatively stable, while the activity of the two enzymes in the plant inoculated with the nematode decreased during 2 to 18 day post inoculation (dpi). These activities increased in inoculated plants treated with C. officinalis, C. mediterranea, and U. fasciata extracts and the other plants treated with Oxamyl 24% SL (5 ml/l). The maximum activity of the three enzymes was recorded at 5 dpi after treatment with U. fasciata.

Enhanced anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aged soil pretreated by hydrogen peroxide

Although integrated chemical-biological treatment of PAHs contaminated soil has received significant attention over the past decades, information is scarce regarding integrated chemical oxidation and anoxic biodegradation of PAHs in contaminated subsurface soil in unsaturated zones. In this study, anoxic biodegradation of PAHs in an aged soil pretreated with hydrogen peroxide (H2O2) was investigated. Anoxic incubation experiment was performed in 50-mL serum bottles containing 30 g of soil and 7 mL of solution, then the soils (moisture, 29.3%; pH, 7.18) were incubated at 30 °C in the dark for 180 days. Apparent removal was observed for 16 USEPA priority PAHs in soil treated with H2O2. The removal percentage of 16 PAHs was 33.2%–95.9%, whereas the application of H2O2 resulted in 3.5 orders of magnitude decrease in the log gene copy number of the bacteria in soil. However, the bacterial numbers rebounded after 180 days of anoxic incubation under favorable conditions (inoculation or/and additional nutrients). The use of either nutrients (CY) or electron acceptor (nitrate, CN) did not enhance the anoxic degradation of PAHs, whereas coupling of both nutrients and electron acceptor led to anoxic biodegradation of PAHs (YN). Moreover, higher anoxic biodegradation efficiency was observed for 3-rings and partial 4-rings PAHs (fluoranthene and pyrene) in inoculated soil than that of non-inoculated soil in treatment YN where both nutrients and electron acceptor were added. The results of this study provide an attractive approach to the removal of PAHs from subsurface soils.

Cyanobacteria Inoculation Improves Soil Stability and Fertility on Different Textured Soils: Gaining Insights for Applicability in Soil Restoration

Cyanobacteria are ubiquitous components of biocrust communities and the first colonizers of terrestrial ecosystems. They play multiple roles in the soil by fixing C and N and synthesizing exopolysaccharides, which increase soil fertility and water retention and improve soil structure and stability. Application of cyanobacteria as inoculants to promote biocrust development has been proposed as a novel biotechnological technique for restoring barren degraded areas and combating desertification processes in arid lands. However, previous to their widespread application under field conditions, research is needed to ensure the selection of the most suitable species. In this study, we inoculated two cyanobacterial species, Phormidium ambiguum (non N-fixing) and Scytonema javanicum (N-fixing), on different textured soils (from silt loam to sandy), and analyzed cyanobacteria biocrust development and evolution of physicochemical soil properties for three months under laboratory conditions. Cyanobacteria inoculation led to biocrust formation in all soil types. Scanning electron microscope (SEM) images showed contrasting structure of the biocrust induced by the two cyanobacteria. The one from P. ambiguum was characterized by thin filaments that enveloped soil particles and created a dense, entangled network, while the one from S. javanicum consisted of thicker filaments that grouped as bunches in between soil particles. Biocrust development, assessed by chlorophyll a content and crust spectral properties, was higher in S. javanicum-inoculated soils compared to P. ambiguum-inoculated soils. Either cyanobacteria inoculation did not increase soil hydrophobicity. S. javanicum promoted a higher increase in total organic C and total N content, while P. ambiguum was more effective in increasing total exopolysaccharide (EPS) content and soil penetration resistance. The effects of cyanobacteria inoculation also differed among soil types and the highest improvement in soil fertility compared to non-inoculated soils was found in sandy and silty soils, which originally had lowest fertility. On the whole, the improvement in soil fertility and stability supports the viability of using cyanobacteria to restore degraded arid soils.

Kinetics study of nicosulfuron degradation by a Pseudomonas nitroreducens strain NSA02.

A bacterial strain NSA02, isolated from contaminated soil and identified as Pseudomonas nitroreducens based on partial 16S rDNA gene sequence analysis and BIOLOG microbiology analysis, was used to study biodegradation of nicosulfuron in the culture medium. The optimal degradation conditions were determined to be 30°C and pH 7.0. Batch tests were performed for seven different initial substrate concentrations to observe substrate degradation and associated cell growth. The biodegradation kinetics was found to follow a first-order model with regression values greater than 0.98. Specific degradation rate and specific growth rate of bacterial cells were observed to follow substrate inhibition kinetics, and the maximum values of both rates were observed at 100mgL-1 of nicosulfuron concentration. Kinetic parameters of three substrate inhibition models (Haldane, Aiba-Edwards and Teissier-Edwards) were fitted to the relationship between those rates and substrate concentrations. With the date obtained, Haldane and Teissier-Edwards models provide better representation when compared to Aiba-Edwards model. Inoculating nicosulfuron-treated soil samples with strain NSA02 resulted in a 5-6 times higher rate of nicosulfuron removal than that in non-inoculated soil. Five metabolites of nicosulfuron degradation were detected and identified by liquid chromatography mass spectrometry, and three possible biotransformation pathways were proposed. These results highlight the potential of the isolated bacterium to be used in the bioremediation of nicosulfuron-contaminated soils.

Degradation of 4-chlorophenol and microbial diversity in soil inoculated with single Pseudomonas sp. CF600 and Stenotrophomonas maltophilia KB2

Soil contamination with chlorophenols is a serious problem all over the world due to their common use in different branches of industry and agriculture. The objective of this study was to determine whether bioaugmenting soil with single Pseudomonas sp. CF600 and Stenotrophomonas maltophilia KB2 and additional carbon sources such as phenol (P) and sodium benzoate (SB) could enhance the degradation of 4-chlorophenol (4-CP). During the degradation experiment, the number of bacteria as well as the structural and functional diversity of the soil microbial communities were determined. It was found that the most effective degradation of 4-CP in the soil was observed after it was inoculated with CF600 and the addition of SB. The biodegradation of five doses of 4-CP in this soil proceeded within 100 days. At the same time, the rate of the disappearance of 4-CP in the soil that had been bioaugmented with CF600 and contaminated with 4-CP and P was 5–6.5 times lower compared to its rate of disappearance in the soil that had been contaminated with 4-CP. The biodegradation of 4-CP in all of the treated and untreated soils was accompanied by a systematic decrease in the number of heterotrophic bacteria (THB) ranging between 13 and 40%. It was also proven that the tested aromatic compounds affected the soil microbial community structure through an increase in the marker fatty acids for Gram-negative bacteria (BG-) and fungi (F). The essential changes in the patterns of the fatty acid methyl esters (FAMEs) for the polluted soil included an increase in the fatty acid saturation and hydroxy fatty acid abundance. The obtained results also indicated that the introduction of CF600 into the soil contaminated with 4-CP and SB or P caused an increase in the functional diversity of the soil microorganisms. In contrast, in the soil that had been inoculated with KB2 and in the non-inoculated soil, the addition of 4-CP and P decreased the microbial activity. In conclusion, the inoculation of both strains into contaminated soil with aromatic compounds caused irreversible changes in the functional and structural diversity of the soil microbial communities.