Insights into the Host Specificity of a New Oomycete Root Pathogen, Pythium brassicum P1: Whole Genome Sequencing and Comparative Analysis Reveals Contracted Regulation of Metabolism, Protein Families, and Distinct Pathogenicity Repertoire.

Pythium brassicum P1 Stanghellini, Mohammadi, Förster, and Adaskaveg is an oomycete root pathogen that has recently been characterized. It only attacks plant species belonging to Brassicaceae family, causing root necrosis, stunting, and yield loss. Since P. brassicum P1 is limited in its host range, this prompted us to sequence its whole genome and compare it to those of broad host range Pythium spp. such as P. aphanidermatum and P. ultimum var. ultimum. A genomic DNA library was constructed with a total of 374 million reads. The sequencing data were assembled using SOAPdenovo2, yielding a total genome size of 50.3 Mb contained in 5434 scaffolds, N50 of 30.2 Kb, 61.2% G+C content, and 13,232 putative protein-coding genes. Pythium brassicum P1 had 175 species-specific gene families, which is slightly below the normal average. Like P. ultimum, P. brassicum P1 genome did not encode any classical RxLR effectors or cutinases, suggesting a significant difference in virulence mechanisms compared to other oomycetes. Pythium brassicum P1 had a much smaller proportions of the YxSL sequence motif in both secreted and non-secreted proteins, relative to other Pythium species. Similarly, P. brassicum P1 had the fewest Crinkler (CRN) effectors of all the Pythium species. There were 633 proteins predicted to be secreted in the P. brassicum P1 genome, which is, again, slightly below average among Pythium genomes. Pythium brassicum P1 had only one cadherin gene with calcium ion-binding LDRE and DxND motifs, compared to Pythium ultimum having four copies. Pythium brassicum P1 had a reduced number of proteins falling under carbohydrate binding module and hydrolytic enzymes. Pythium brassicum P1 had a reduced complement of cellulase and pectinase genes in contrast to P. ultimum and was deficient in xylan degrading enzymes. The contraction in ABC transporter families in P. brassicum P1 is suggested to be the result of a lack of diversity in nutrient uptake and therefore host range.

Structure and ecological function of the soil microbiome affecting plant-soil feedbacks in the presence of a soil-borne pathogen.

Interactions between plants and soil microbes are important for plant growth and resistance. Through plant-soil-feedbacks, growth of a plant is influenced by the previous plant that was growing in the same soil. We performed a plant-soil feedback study with 37 grass, forb and legume species, to condition the soil and then tested the effects of plant-induced changes in soil microbiomes on the growth of the commercially important cut-flower Chrysanthemum in presence and absence of a pathogen. We analysed the fungal and bacterial communities in these soils using next-generation sequencing and examined their relationship with plant growth in inoculated soils with or without the root pathogen, Pythium ultimum. We show that a large part of the soil microbiome is plant species-specific while a smaller part is conserved at the plant family level. We further identified clusters of plant species creating plant growth promoting microbiomes that suppress concomitantly plant pathogens. Especially soil inocula with higher relative abundances of arbuscular mycorrhizal fungi caused positive effects on the Chrysanthemum growth when exposed to the pathogen. We conclude that plants differ greatly in how they influence the soil microbiome and that plant growth and protection against pathogens is associated with a complex soil microbial community.

Genome-wide sequencing and metabolic annotation of Pythium irregulare CBS 494.86: understanding Eicosapentaenoic acid production.

BACKGROUND: Pythium irregulare is an oleaginous Oomycete able to accumulate large amounts of lipids, including Eicosapentaenoic acid (EPA). EPA is an important and expensive dietary supplement with a promising and very competitive market, which is dependent on fish-oil extraction. This has prompted several research groups to study biotechnological routes to obtain specific fatty acids rather than a mixture of various lipids. Moreover, microorganisms can use low cost carbon sources for lipid production, thus reducing production costs. Previous studies have highlighted the production of EPA by P. irregulare, exploiting diverse low cost carbon sources that are produced in large amounts, such as vinasse, glycerol, and food wastewater. However, there is still a lack of knowledge about its biosynthetic pathways, because no functional annotation of any Pythium sp. exists yet. The goal of this work was to identify key genes and pathways related to EPA biosynthesis, in P. irregulare CBS 494.86, by sequencing and performing an unprecedented annotation of its genome, considering the possibility of using wastewater as a carbon source. RESULTS: Genome sequencing provided 17,727 candidate genes, with 3809 of them associated with enzyme code and 945 with membrane transporter proteins. The functional annotation was compared with curated information of oleaginous organisms, understanding amino acids and fatty acids production, and consumption of carbon and nitrogen sources, present in the wastewater. The main features include the presence of genes related to the consumption of several sugars and candidate genes of unsaturated fatty acids production. CONCLUSIONS: The whole metabolic genome presented, which is an unprecedented reconstruction of P. irregulare CBS 494.86, shows its potential to produce value-added products, in special EPA, for food and pharmaceutical industries, moreover it infers metabolic capabilities of the microorganism by incorporating information obtained from literature and genomic data, supplying information of great importance to future work.

The application of safe for humans and the environment Polyversum antifungal agent containing living cells of Pythium oligandrum for biotransformation of prochiral ketones.

This report presents the whole-cell biotransformation of benzofuranyl-methyl ketone derivatives with the application of Polyversum antifungal agent containing Pythium oligandrum microorganism. Stereochemistry of the reduction of prochiral substrates was modified by the bioconversion conditions (concentration of reagents, a source of the carbon atom, biotransformation medium). In optimized conditions enantioselective process was noted. Secondary alcohols with excellent enantiomeric purity and high yields were obtained. The enantiomeric excess and conversion degree of 1-(benzofuran-2-yl)ethanol, 1-(7-ethylbenzofuran-2-yl)ethanol and 1-(3,7-dimethylbenzofuran-2-yl)ethanol were 99%/98.1%, 94%/94.4% and 99%/72.6%, respectively. In the presence of P. oligandrum, one of the enantiotopic hydrides of the dihydropyridine ring coenzyme is selectively transferred to a re side of the prochiral carbonyl group to give products with S configuration. This study demonstrates an inexpensive, eco-friendly approach in synthesis of optically pure benzofuran derivatives and can be an interesting alternative to organocatalysis. Furthermore, this method can be used in biotechnology processes due to its good chemical performance and a high degree of product isolation.

The cytochrome bc1 complex inhibitor Ametoctradin has an unusual binding mode.

Ametoctradin is an agricultural fungicide that selectively inhibits the cytochrome bc1 complex of oomycetes. Previous spectrophotometric studies using the purified cytochrome bc1 complex from Pythium sp. showed that Ametoctradin binds to the Qo-site of the enzyme. However, as modeling studies suggested a binding mode like that of the substrate ubiquinol, the possibility for a dual Qo- and Qi-site binding mode was left open. In this work, binding studies and enzyme assays with mitochondrial membrane preparations from Pythium sp. and an S. cerevisiae strain with a modified Qi-site were used to investigate further the binding mode of Ametoctradin. The results obtained argue that the compound could bind to both the Qo- and Qi-sites of the cytochrome bc1 complex and that its position or binding pose in the Qi-site differs from that of Cyazofamid and Amisulbrom, the two Qi-site-targeting, anti-oomycetes compounds. Furthermore, the data support the argument that Ametoctradin prefers binding to the reduced cytochrome bc1 complex. Thus, Ametoctradin has an unusual binding mode and further studies with this compound may offer the opportunity to better understand the catalytic cycle of the cytochrome bc1 complex.

Protein profile of Brazilian Pythium insidiosum isolates.

Pythium insidiosum is an important aquatic Oomycota that causes pythiosis in mammals, especially horses, dogs, and humans; these inhabit marshy environments in tropical and subtropical areas. The aim of this study was to determine the protein profile, as well as identify likely immunodominant proteins, of Brazilian P. insidiosum isolates from southern Brazil, an important equine pythiosis endemic area. P. insidiosum isolates (horses, n = 20 and dogs, n = 02) were analyzed by SDS-PAGE and Western blot techniques. Horse, cattle, dog, and rabbit sera of both diseased and healthy animals were used to identify P. insidiosum proteins. SDS-PAGE protein profile detected antigens of molecular weights ranging from 100 to 20 KDa. Dog isolates revealed a protein profile similar to that of horse isolates. Anti-P. insidiosum antibodies in the sera of the four species could recognize proteins of different molecular weights (∼74 KDa to ∼24 KDa), and proteins ∼50-55 KDa and ∼34 KDa were shown to be immunodominant. Furthermore, ∼74 KDa, ∼60 KDa, ∼30 KDa and ∼24 KDa proteins were poorly recognized by host species antibodies. The Brazilian P. insidiosum isolates analyzed showed a similar protein profile; however, further studies are essential for the identification and characterization of proteins expressed by P. insidiosum, and an evaluation of the immunological profile of hosts susceptible to this Oomycota is necessary.

Evolution of the Sterol Biosynthetic Pathway of Pythium insidiosum and Related Oomycetes Contributes to Antifungal Drug Resistance.

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum Direct exposure to Py. insidiosum zoospores can initiate infections of the eye, limb, gastrointestinal tract, or skin/subcutaneous tissue. Treatments for pythiosis have mostly relied on surgery. Antifungal drugs are generally ineffective against Py. insidiosum However, one patient with an invasive Py. insidiosum infection recovered completely following treatment with terbinafine and itraconazole. Additionally, the drug target sterol biosynthetic enzymes have been identified in the oomycete Aphanomyces euteiches It remains an open question whether Py. insidiosum is susceptible to the antifungal drugs and harbors any of the known drug target enzymes. Here, we determined the in vitro susceptibilities of terbinafine and itraconazole against 30 isolates of Py. insidiosum We also analyzed endogenous sterols and searched for genes encoding the sterol biosynthetic enzymes in the genomes of Py. insidiosum and related oomycetes. The susceptibility assay showed that the growth of each of the Py. insidiosum isolates was inhibited by the antifungal agents, but only at difficult-to-achieve concentrations, which explains the clinical resistance of the drugs in the treatment of pythiosis patients. Genome searches of Py. insidiosum and related oomycetes demonstrated that these organisms contained an incomplete set of sterol biosynthetic enzymes. Gas chromatographic mass spectrometry did not detect any sterol end products in Py. insidiosum In conclusion, Py. insidiosum possesses an incomplete sterol biosynthetic pathway. Resistance to antifungal drugs targeting enzymes in the ergosterol biosynthetic pathway in Py. insidiosum was due to modifications or losses of some of the genes encoding the drug target enzymes.

Improved eicosapentaenoic acid production in Pythium splendens RBB-5 based on metabolic regulation analysis.

Eicosapentaenoic acid (EPA) is an essential polyunsaturated fatty acid for human beings. At present, the production of commercially available long-chain polyunsaturated fatty acids, mainly from wild-caught ocean fish, is struggling to meet the increasing demand for EPA. Production of EPA by microorganisms may be an alternative, effective and economical method. The oleaginous fungus Pythium splendens RBB-5 is a potential source of EPA, and thanks to the simple culture conditions required, high yields can be achieved in a facile manner. In the study, lipid metabolomics was performed in an attempt to enhance EPA biosynthesis in Pythium splendens. Synthetic, metabolic regulation and gene expression analyses were conducted to clarify the mechanism of EPA biosynthesis, and guide optimization of EPA production. The results showed that the Δ6 desaturase pathway is the main EPA biosynthetic route in this organism, and ∆6, ∆12 and Δ17 desaturases are the rate-limiting enzymes. All the three desaturase genes were separately introduced into the parent strain to increase the flow of fatty acids into the Δ6 desaturase pathway. Enhanced expression of these key enzymes, in combination with improved regulation of metabolism, resulted in a maximum yield of 1.43 g/L in the D12 transgenic strain, which represents a tenfold increase over the parent strain before optimization. This is the higher EPA production yield yet reported for a microbial system. Our findings may allow the production of EPA at an industrial scale, and the strategy employed could be used to increase the production of EPA or other lipids in oleaginous microorganisms.

Ag nanoparticles generated using bio-reduction and -coating cause microbial killing without cell lysis.

Cost-effective "green" methods of producing Ag nanoparticles (NPs) are being examined because of the potential of these NPs as antimicrobials. Ag NPs were generated from Ag ions using extracellular metabolites from a soil-borne Pythium species. The NPs were variable in size, but had one dimension less than 50 nm and were biocoated; aggregation and coating changed with acetone precipitation. They had dose-dependent lethal effects on a soil pseudomonad, Pseudomonas chlororaphis O6, and were about 30-fold more effective than Ag(+) ions. A role of reactive oxygen species in cell death was demonstrated by use of fluorescent dyes responsive to superoxide anion and peroxide accumulation. Also mutants of the pseudomonad, defective in enzymes that protect against oxidative stress, were more sensitive than the wild type strain; mutant sensitivity differed between exposure to Ag NPs and Ag(+) ions demonstrating a nano-effect. Imaging of bacterial cells treated with the biocoated Ag NPs revealed no cell lysis, but there were changes in surface properties and cell height. These findings support that biocoating the NPs results in limited Ag release and yet they retained potent antimicrobial activity.

Pesticidal activity of metal oxide nanoparticles on plant pathogenic isolates of Pythium.

CuO and ZnO nanoparticles (NPs) have antimicrobial effects that could lead to formulations as pesticides for agriculture or medicine. The responses of two soil-borne plant pathogenic Pythium isolates to the NPs were studied to determine the potential of these metal oxide NPs as pesticides. Growth of the P. ultimum isolate was more sensitive to CuO NPs than the P. aphanidermatum isolate. Growth in liquid medium with CuO NPs eliminated culturability whereas exposure to ZnO NPs resulted in stasis with growth resuming on transfer to medium lacking NPs. The citrate in the medium used for the growth assays was involved in enhanced release of the toxic metals from the NPs. Both CuO and ZnO NPs affected processes involved in Fe uptake. The NPs reduced levels of Fe-chelating siderophore-like metabolites produced by Pythium hyphae. CuO NPs inhibited, but ZnO NPs increased, ferric reductase activity detected at the mycelial surface. These findings illustrate that the toxicity of the metal oxide NPs towards Pythium was influenced by the medium, especially by the presence of a metal chelator. Environmental factors are likely to alter the pesticide potential of the metal oxide NPs when formulated for agricultural use in soils.

[Toxicity of Pythium oligandrum broth to animal and its control effect on rot diseases caused by Penicillium italicum and Penicillium digitatum in orange fruit storage].

OBJECTIVE: In order to develop a safe, nontoxic and efficient biological antistaling agent and to decrease the incidence of rot diseases caused by the Penicillium italicum and Penicillium digitatum in orange fruit storage. METHODS: the present experiment was carried out with Pythium oligandrum broth (POB) produced by our self-isolated strain (P. oligandrum CQ2010) to study the toxicity to animal. Thereafter, mycelium growth and spore germination of both P. digitatum and P. italicum and control effect of rot disease in orange storage were compared after treated by liquid culture medium (control), POB, prochloraz (PC) , and PC + POB. RESULTS: Gastric lavage with large amount POB did not influence mouse weight. The animals also showed no abnormality in appearance, behaviors and pathology changes in heart, liver, kidney, lung and intestine. POB decreased the hyphal growth by 70.24% - 93.74% and spore germination by 44.91% - 87.82% (24 h after POB addition) of these two pathogenic fungi. Disease incidence of orange fruit following P. italicum inoculation changed in the sequence: CK > POB > PC > PC + POB and the control efficacy behaved otherwise. In commercial simulation storage, the disease incidence of orange fruit caused by P. digitatum and P. italicum was above 50% of the total. The fruit rot rate was 26.40% (CK), 15.03% (POB), 16.61% (PC) and 4.21% (PC + POB). There were no significant differences in fruit quality under different treatments. CONCLUSION: POB was safe to animal and could decrease rot disease incidence caused by P. italicum and P. digitatum in orange storage whereby producing a positive interaction with prochloraz and controlling rot diseases caused by these two fungi.

Isolation, characterization, and formulation of antagonistic bacteria for the management of seedlings damping-off and root rot disease of cucumber.

Antagonistic bacteria are common soil inhabitants with potential to be developed into biofungicides for the management of seedling damping-off, root rot, and other soil-borne diseases of various crops. In this study, antagonistic bacteria were isolated from a commercial potato field and screened for their growth inhibition of fungal and oomycete pathogens in laboratory tests. The biocontrol potential of the 3 most effective antagonistic bacteria from the in vitro tests was evaluated against seedling damping-off and root rot of cucumber caused by Pythium ultimum. Based on phenotypic characteristics, biochemical tests, and sequence analysis of 16S-23S rDNA gene, the 3 antagonistic bacteria were identified as Pseudomonas fluorescens (isolate 9A-14), Pseudomonas sp. (isolate 8D-45), and Bacillus subtilis (isolate 8B-1). All 3 bacteria promoted plant growth and suppressed Pythium damping-off and root rot of cucumber seedlings in growth-room assays. Both pre- and post-planting application of these bacteria to an infested peat mix significantly increased plant fresh masses by 113%-184% and percentage of healthy seedlings by 100%-290%, and decreased damping-off and root rot severity by 27%-50%. The peat and talc formulations of these antagonistic bacteria applied as seed or amendment treatments to the infested peat mix effectively controlled Pythium damping-off and root rot of cucumber seedlings and enhanced plant growth. The survival of all 3 antagonistic bacteria in peat and talc formulations decreased over time at room temperature, but the populations remained above 10(8) CFU/g during the 180-day storage period. The peat formulation of a mixture of 3 bacteria was the best seed treatment, significantly increasing the plant fresh masses by 245% as compared with the Pythium control, and by 61.4% as compared with the noninfested control. This study suggests that the indigenous bacteria from agricultural soils can be developed and formulated as biofungicides for minimizing the early crop losses caused by seedling damping-off and root rot diseases.

Potential anti-Pythium insidiosum therapeutics identified through screening of agricultural fungicides.

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum. Clinical manifestations of pythiosis include an eye, blood vessel, skin, or gastrointestinal tract infection. Pythiosis has been increasingly reported worldwide, with an overall mortality rate of 28%. Radical surgery is required to save patients' lives due to the limited efficacy of antimicrobial drugs. Effective medical treatments are urgently needed for pythiosis. This study aims to find anti-P. insidiosum agents by screening 17 agricultural fungicides that inhibit plant-pathogenic oomycetes and validating their efficacy and safety. Cyazofamid outperformed other fungicides as it can potently inhibit genetically diverse P. insidiosum isolates while exhibiting minimal cellular toxicities. The calculated therapeutic scores determined that the concentration of cyazofamid causing significant cellular toxicities was eight times greater than the concentration of the drug effectively inhibiting P. insidiosum. Furthermore, other studies showed that cyazofamid exhibits low-to-moderate toxicities in animals. The mechanism of cyazofamid action is likely the inhibition of cytochrome b, an essential component in ATP synthesis. Molecular docking and dynamic analyses depicted a stable binding of cyazofamid to the Qi site of the P. insidiosum's cytochrome b orthologous protein. In conclusion, our search for an effective anti-P. insidiosum drug indicated that cyazofamid is a promising candidate for treating pythiosis. With its high efficacy and low toxicity, cyazofamid is a potential chemical for treating pythiosis, reducing the need for radical surgeries, and improving recovery rates. Our findings could pave the way for the development of new and effective treatments for pythiosis.IMPORTANCEPythiosis is a severe infection caused by Pythium insidiosum. The disease is prevalent in tropical/subtropical regions. This infectious condition is challenging to treat with antifungal drugs and often requires surgical removal of the infected tissue. Pythiosis can be fatal if not treated promptly. There is a need for a new treatment that effectively inhibits P. insidiosum. This study screened 17 agricultural fungicides that target plant-pathogenic oomycetes and found that cyazofamid was the most potent in inhibiting P. insidiosum. Cyazofamid showed low toxicity to mammalian cells and high affinity to the P. insidiosum's cytochrome b, which is involved in energy production. Cyazofamid could be a promising candidate for the treatment of pythiosis, as it could reduce the need for surgery and improve the survival rate of patients. This study provides valuable insights into the biology and drug susceptibility of P. insidiosum and opens new avenues for developing effective therapies for pythiosis.

The safety assessment of Pythium irregulare as a producer of biomass and eicosapentaenoic acid for use in dietary supplements and food ingredients.

Polyunsaturated fatty acids, docosahexaenoic acid (DHA, 22:6, n-3), eicosapentaenoic acid (EPA, 20:5, n-3), and arachidonic acid (ARA, 20:4 n-6), have multiple beneficial effects on human health and can be used as an important ingredient in dietary supplements, food, feed and pharmaceuticals. A variety of microorganisms has been used for commercial production of these fatty acids. The microorganisms in the Pythium family, particularly Pythium irregulare, are potential EPA producers. The aim of this work is to provide a safety assessment of P. irregulare so that the EPA derived from this species can be potentially used in various commercial applications. The genus Pythium has been widely recognized as a plant pathogen by infecting roots and colonizing the vascular tissues of various plants such as soybeans, corn and various vegetables. However, the majority of the Pythium species (including P. irregulare) have not been reported to infect mammals including humans. The only species among the Pythium family that infects mammals is P. insidiosum. There also have been no reports showing P. irregulare to contain mycotoxins or cause potentially allergenic responses in humans. Based on the safety assessment, we conclude that P. irregulare can be considered a safe source of biomass and EPA-containing oil for use as ingredients in dietary supplements, food, feed and pharmaceuticals.

Identification of a fatty acid ∆(6)-desaturase gene from the eicosapentaenoic acid-producing fungus Pythium splendens RBB-5.

A new full-length cDNA (PsD6) putatively encoding a ∆(6)-desaturase was cloned from the eicosapentaenoic acid-producing fungus Pythium splendens RBB-5. PsD6 contained an open reading frame of 1380 bp encoding a protein of 459 amino acids. The deduced amino acid sequence showed high similarity to those of other ∆(6)-desaturases. A recombinant vector expressing PsD6 (pPIC3.5K-D6) was constructed and transformed into Pichia pastoris GS115. The heterologous expressed PsD6 in P. pastoris desaturated linoleic acid to γ-linolenic acid but not desaturated α-linolenic acid to stearidonic acid. The results indicated that PsD6 was a fatty acid ∆(6)-desaturase and it had a substrate specificity for linoleic acid.

Mycelia promote active transport and spatial dispersion of polycyclic aromatic hydrocarbons.

To cope with heterogeneous subsurface environments mycelial microorganisms have developed a unique ramified growth form. By extending hyphae, they can obtain nutrients from remote places and transport them even through air gaps and in small pore spaces, repectively. To date, studies have been focusing on the role that networks play in the distribution of nutrients. Here, we investigated the role of mycelia for the translocation of nonessential substances, using polycyclic aromatic hydrocarbons (PAHs) as model compounds. We show that the hyphae of the mycelial soil oomycete Pythium ultimum function as active translocation vectors for a wide range of PAHs. Visualization by two-photon excitation microscopy (TPEM) demonstrated the uptake and accumulation of phenanthrene (PHE) in lipid vesicles and its active transport by cytoplasmic streaming of the hyphae ('hyphal pipelines'). In mycelial networks, contaminants were translocated over larger distances than by diffusion. Given their transport capacity and ubiquity, hyphae may substantially distribute remote hydrophobic contaminants in soil, thereby improving their bioavailability to bacterial degradation. Hyphal contaminant dispersal may provide an untapped potential for future bioremediation approaches.

Altering in vivo membrane sterol composition affects the activity of the cyclic lipopeptides tolaasin and sessilin against Pythium.

Cyclic lipopeptides (CLiPs) are secondary metabolites produced by a variety of bacteria. These compounds show a broad range of antimicrobial activities; therefore, they are studied for their potential applications in agriculture and medicine. It is generally assumed that the primary target of the CLiPs is the cellular membrane, where they can permeabilize the lipid bilayer. Model membrane systems are commonly used to investigate the effect of lipid composition on the permeabilizing activity of CLiPs, but these systems do not represent the full complexity of true biological membranes. Here, we introduce a novel method that uses sterol-auxotrophic oomycetes to investigate how the activity of membrane-active compounds is influenced by alterations in membrane sterol composition. More specifically, we investigated how ergosterol, cholesterol, beta-sitosterol and stigmasterol affect the activity of the structurally related Pseudomonas-derived CLiPs tolaasin and sessilin against the oomycete Pythium myriotylum. Both compounds were effective against oomycetes, although tolaasin was considerably more active. Interestingly, tolaasin and sessilin effects were similarly reduced by the presence of sterols, with cholesterol showing the highest reduction of activity.

Hexavalent chromium sorption by biomass of chromium tolerant Pythium sp.

The removal of Cr(VI) from aqueous solutions by live and pretreated fungal biomass of Pythium sp was investigated in a batch mode. The influence of biomass dose, solution pH, initial metal ion concentration, temperature and pretreatment of biomass on biosorption efficiency was studied. The acid pretreated biomass adsorbed 1.7 times more hexavalent chromium in comparison to untreated biomass. The chromium removal rate increased with decrease in pH and increase in Cr(VI) concentration, biomass dose and temperature. The adsorption data was described well by Freundlich isotherm model. Evaluation of biosorption mechanism using infrared spectroscopy showed the involvement of positively charged amino groups in Cr(VI) biosorption. The biosorption of Cr(VI) by Pythium sp. followed second order kinetics, the biosorption process was found to be spontaneous and endothermic with high affinity of biomass for Cr(VI).

Fungal mycelia allow chemotactic dispersal of polycyclic aromatic hydrocarbon-degrading bacteria in water-unsaturated systems.

Contaminant biodegradation in soil is frequently limited by hindered physical access of bacteria to the contaminants. In the frame of the development of novel bioremediation approaches based on ecological principles, we tested the hypothesis that fungal networks facilitate the movement of bacteria by providing continuous liquid films in which gradients of chemoattractants can form and chemotactic swimming can take place. Unlike bacteria, filamentous fungi spread with ease in water-unsaturated soil. In a simple laboratory model of a water-unsaturated environment, we studied the movement of polycyclic aromatic hydrocarbon-degrading Pseudomonas putida PpG7 (NAH7) along a mycelium of Pythium ultimum. Some undirected dispersal was observed in the absence of a chemoattractant or when the non-chemotactic derivative strain P. putida G7.C1 (pHG100) was used. The bacterial movement became fourfold more effective and clearly directed when the chemotactic wild type was used and salicylate was present as a chemoattractant. No dispersal of bacteria was found in the absence of the fungus. These findings point at a role of mycelia for the translocation of chemicals and microorganisms. The results suggest that fungi improve the accessibility of contaminants in water-unsaturated environments.

Long-Read Genome Sequence of the Sugar Beet Rhizosphere Mycoparasite Pythium oligandrum.

Pythium oligandrum is a soil born free living oomycete able to parasitize fungi and oomycetes prey, including important plant and animals pathogens. Pythium oligandrum can colonize endophytically the root tissues of diverse plants where it induces plant defenses. Here we report the first long-read genome sequencing of a P. oligandrum strain sequenced by PacBio technology. Sequencing of genomic DNA loaded onto six SMRT cells permitted the acquisition of 913,728 total reads resulting in 112X genome coverage. The assembly and polishing of the genome sequence yielded180 contigs (N50 = 1.3 Mb; L50 = 12). The size of the genome assembly is 41.9 Mb with a longest contig of 2.7 Mb and 15,007 predicted protein-coding genes among which 95.25% were supported by RNAseq data, thus constituting a new Pythium genome reference. This data will facilitate genomic comparisons of Pythium species that are commensal, beneficial or pathogenic on plant, or parasitic on fungi and oomycete to identify key genetic determinants underpinning their diverse lifestyles. In addition comparison with plant pathogenic or zoopathogenic species will illuminate genomic adaptations for pathogenesis toward widely diverse hosts.