Alginate embedding and subsequent sporulation of in vitro-produced Conidiobolus thromboides hyphae using a pressurised air-extrusion method

Conidiobolus thromboides is an entomophthoralean fungus with potential as a biological control agent of aphids. However, its application in biological control is limited due to its formulation requirements. The objective of this study was to develop and optimise a novel air-extrusion method to embed C. thromboides hyphae at high density in alginate pellets. An orthogonal experimental design was used to investigate selected combinations of parameters known to affect hyphal density within pellets. The diameter of pellets produced, and the calculated density of hyphae within them, ranged from 0.18 ± 0.09 to 3.17 ± 0.06 mm and from 0.02 to 350.56 mg/mm³ respectively. These data were used to predict the optimal parameter combination to deliver the greatest density of hyphae of C. thromboides per pellet: 1% sodium alginate, a 1:2 ratio of hyphae to sodium alginate, an orifice diameter of 0.232 mm and an air pressure of 0.05 MPa. Pellets made under the optimal conditions predicted produced a mean total of 4.3 ± 0.6 × 10⁵ conidia per pellet at 100% relative humidity which was significantly greater than the mean total number of conidia produced from infected aphid cadavers of comparable size (9.35 ± 0.85 × 10⁴) (p < 0.001). In conclusion, air-extrusion embedding appears to be a promising method for formulating in vitro-produced hyphae of C. thromboides for use in biological control.     

Lacipirellula parvula gen. nov., sp. nov., representing a lineage of planctomycetes widespread in low-oxygen habitats,description of the family Lacipirellulaceae fam. nov. and proposal of the orders Pirellulales ord. nov., Gemmatales ord. nov. and Isosphaerales ord. nov.

Pirellula-like planctomycetes are ubiquitous aquatic bacteria, which are often detected in anoxic or micro-oxic habitats. By contrast, the taxonomically described representatives of these bacteria, with very few exceptions, are strict aerobes. Here, we report the isolation and characterization of the facultatively anaerobic planctomycete, strain PX69^T, which was isolated from a boreal lake. Its 16S rRNA gene sequence is affiliated with the Pirellula-related Pir4 clade, which is dominated by environmental sequences retrieved from a variety of low-oxygen habitats. Strain PX69^T was represented by ellipsoidal cells that multiplied by budding and grew on sugars, some polysaccharides and glycerol. Anaerobic growth occurred by means of fermentation. Strain PX69^T grew at pH 5.5–7.5 and at temperatures between 10 and 30 °C. The major fatty acids were C18:1ω9c, C16:0 and C16:1ω7c; the major intact polar lipid was dimethylphosphatidylethanolamine. The complete genome of strain PX69^T was 6.92 Mb in size; DNA G + C content was 61.7 mol%. Among characterized planctomycetes, the highest 16S rRNA gene similarity (90.4%) was observed with ‘Bythopirellula goksoyri’ Pr1d, a planctomycete from deep-sea sediments. We propose to classify PX69^T as a novel genus and species, Lacipirellula parvula gen. nov., sp. nov.; the type strain is strain PX69^T (=KCTC 72398^T = CECT 9826^T = VKM B-3335^T). This genus is placed in a novel family, Lacipirellulaceae fam. nov., which belongs to the order Pirellulales ord. nov. Based on the results of comparative genome analysis, we also suggest establishment of the orders Gemmatales ord. nov. and Isosphaerales ord. nov. as well as an emendation of the order Planctomycetales.     

The parasitic and lethal effects of Trichoderma longibrachiatum against Heterodera avenae

Heterodera avenae is a devastating plant pathogen that causes significant yield losses in many crops, but there is a lack of scientific information whether this pathogen can be controlled effectively using biocontrol agents. Here we determined the parasitic and lethal effects of Trichoderma longibrachiatum against H. avenae and the possible mechanism involved in this action. Both in vitro and greenhouse experiments were conducted. In vitro, T. longibrachiatum at the concentrations of 1.5 × 10⁴ to 1.5 × 10⁸ spores per ml had a strong parasitic and lethal effect on the cysts of H. avenae, with the concentration of 1.5 × 10⁸ spores per ml having >90% parasitism 18 days after treatments. In greenhouse, T. longibrachiatum inoculation decreased H. avenae infection in wheat (Triticum aestivum) significantly. Observations with microscopes revealed that after mutual recognition with cysts, the spore of T. longibrachiatum germinated with a large number of hyphae, and reproduced rapidly on the surface of cysts. Meanwhile, the cysts surface became uneven, with some cysts producing vacuoles, and the others splitting. Finally the cysts were dissolved by the metabolite of T. longibrachiatum. Chitinase activity increased in the culture filtrates of T. longibrachiatum and reached the maximum 4 days after inoculation in the medium supplemented with colloidal chitin (1.02 U/min per ml) and nematode cysts (0.78 U/min per ml). The parasitism and inhibition of cysts through the increased extracellular chitinase activity serves as the main mechanism with which T. longibrachiatum against H. avenae. In conclusion, T. longibrachiatum has a great potential to be used as a biocontrol agent against H. avenae.     

Isolation and characterization of a new strain of Methanothermobacter marburgensis DX01 from hot springs in China

Strain DX01, a thermophilic methanogen, was isolated from a hot spring in China. Strain DX01 grew only on H₂/CO₂. The DNA G + C content is 52 mol% and optimal growth temperature is 65 °C. The cell pellet is brick red. By analyzing 16S rRNA sequence, methyl-coenzyme M reductase I, gamma subunit protein sequences, we determined the DX01 strain to be closely related to the species of Methanothermobacter marburgensis. In addition, Methanothermobacter thermautotrophicus delta H^T and strain DX01 had clear differences in their biochemical composition and protein expression profiles. Based on the above analysis, we propose that strain DX01 is a novel strain within thermoautotrophicus the species of M. marburgensis, namely M. marburgensis DX01. The isolation and characterization of the new M. marburgensis DX01 strain expands the known range of the Methanothermobacter genus.     

Assessment of oral virulence against Spodoptera litura,acquired by a previously non-pathogenic Metarhizium anisopliae isolate,following integration of a midgut-specific insecticidal toxin

All entomopathogenic fungi infect insects by direct penetration through the cuticle rather than per os through the gut. Genetic transformation can confer fungi with per os virulence. However, unless the recipient isolate is nonpathogenic to the target insect, mortality caused by a transgenic isolate cannot be attributed solely to oral virulence due to the potential for some simultaneous cuticular infection. Here, a Metarhizium anisopliae wild-type isolate (MaWT) nonpathogenic to Spodoptera litura was genetically engineered to provide a transformed isolate (MaVipT31) expressing the insect midgut-specific toxin Vip3Aa1. Toxin expression was confirmed in MaVipT31 hyphae and conidia using Western blotting. Mortality, leaf consumption and body weight of S. litura larvae (instars I–IV) exposed to a range of concentrations of MaWT conidia were not significantly different to controls although the number of conidia ingested by surviving larvae during the bioassay ranged from 2.3 × 10⁵ (instar I) to 8.1 × 10⁶ (instar IV). In contrast, consumption of MaVipT31 conidia caused high mortalities, reduced leaf consumption rates and decreased body weights in all instars evaluated, demonstrating that oral virulence had been acquired by MaVipT31. Larval mortalities were much more dependent on the number of MaVipT31 conidia ingested than the duration of time spent feeding on conidia-treated leaves (r²: 0.83–0.94 for instars I–IV). LC₅₀ and LT₅₀ trends for MaVipT31 estimated by time-concentration-mortality modeling analyses differed greatly amongst the instars. For 50% kill to be achieved, instar I larvae required 3, 4 and 5 days feeding on the leaves bearing 103, 28 and 8 conidia/mm² respectively; instar IV larvae required 6, 7 and 8 days feeding on leaves bearing 1760, 730 and 410 conidia/mm² respectively. Our results provide a deeper insight into the high oral virulence acquired by an engineered isolate and highlight its great potential for biological control.     

Proposal of Desulfosarcina ovata subsp. sediminis subsp. nov., a novel toluene-degrading sulfate-reducing bacterium isolated from tidal flat sediment of Tokyo Bay

Strain 28bB2T^T is a sulfate-reducing bacterium isolated in a previous study, obtained from a p-xylene-degrading enrichment culture. Physiological, phylogenetic and genomic characterizations of strain 28bB2T^T were performed to establish the taxonomic status of the strain. Cells of strain 28bB2T^T were short oval-shaped (0.8–1.2 × 1.2–2.7 μm), motile, and Gram-negative. For growth, the optimum pH was pH 6.5–7.0 and the optimum temperature was 28–32 °C. Strain 28bB2T^T oxidized toluene but could not utilize p-xylene. Sulfate and thiosulfate were used as electron acceptors. The G + C content of the genomic DNA was 53.8 mol%. The genome consisted of an approximately 8.3 Mb of chromosome and two extrachromosomal elements. On the basis of 16S rRNA gene analysis, strain 28bB2T^T was revealed to belong to the genus Desulfosarcina, with high sequence identities to Desulfosarcina ovata oXyS1^T (99.5%) and Desulfosarcina cetonica DSM 7267^T (98.7%). Results of Average Nucleotide Identity (ANI) calculation and digital DNA–DNA hybridization (dDDH) analysis showed that the strain 28bB2T^T should be classified as a subspecies under D. ovata. Based on physiological and phylogenetic data, strain 28bB2T^T (=NBRC 106234 =DSM 23484) is proposed as the type strain of a novel species in genus Desulfosarcina, Desulfosarcina ovata subsp. sediminis subsp. nov.     

Marinitoga lauensis sp. nov., a novel deep-sea hydrothermal vent thermophilic anaerobic heterotroph with a prophage

A novel moderately thermophilic, heterotrophic anaerobe, designated strain LG1^T, was isolated from the Mariner deep-sea hydrothermal vent field along the Eastern Lau Spreading Center and Valu Fa Ridge. Cells of strain LG1^T were motile rods, occurring singly or in pairs, 0.6 μm in width and 1.2 μm in length. The strain LG1^T grew between 40 and 70 °C (optimum 50–55 °C), at a pH between 5 and 8 (optimum pH 6.5) and with 7.5–50 g L⁻¹ NaCl (optimum 30 g L⁻¹). Sulfur, cystine and thiosulfate were reduced to sulfide, and cell yield was improved in the presence of cystine. Strain LG1^T was an organotroph able to use a variety of organic compounds. Phylogenetic analysis based on 16S rRNA gene sequence comparisons indicated that strain LG1^T was affiliated to the genus Marinitoga within the order Petrotogales. It shared 95.34–96.31% 16S rRNA gene sequence similarity with strains of other Marinitoga species, and is most closely related to Marinitoga okinawensis. Genome analysis revealed the presence of a prophage sharing high sequence homology with the viruses MPV1, MCV1 and MCV2 hosted by Marinitoga strains. Based on the data from the phylogenetic analyses and the physiological properties of the novel isolate, we propose that strain LG1^T is a representative of a novel species, for which the name Marinitoga lauensis sp. nov. is proposed; the type strain is LG1^T (=DSM 106824 = JCM 32613).     

Bacillus amyloliquefaciens GB1 can effectively control apple valsa canker

Apple valsa canker (AVC), caused by Valsa mali, is one of the most serious diseases of apple trees in eastern Asia, and the most important factor limiting apple production in China. This disease is difficult to control by chemical and agricultural measures, thus biocontrol may constitute a desirable alternative strategy. A Bacillus amyloliquefaciens strain denoted GB1 isolated from ageing cucumber stems, exhibited a strong antagonistic activity against V. mali, inhibiting significantly the germination of conidia and the growth of hyphae. GB1 conidial suspensions (above 10⁶ CFU/ml) applied prior to wound inoculation of apple twigs with V. mali resulted in total inhibition of infection. Strain GB1 colonized xylem and phloem tissues surrounding the wounds made on apple twigs and formed biofilms over them. Results indicate that B. amyloliquefaciens GB1 may be a promising agent for the biocontrol of AVC, and provide new insights into the ability of B. amyloliquefaciens to colonize apple trees.     

Flavobacterium circumlabens sp. nov. and Flavobacterium cupreum sp. nov., two psychrotrophic species isolated from Antarctic environmental samples

A taxonomic study of 24 Gram-stain-negative rod-shaped bacteria originating from the Antarctic environment is described. Phylogenetic analysis using 16S rRNA gene sequencing differentiated isolated strains into two groups belonging to the genus Flavobacterium. Group I (n = 20) was closest to Flavobacterium aquidurense WB 1.1-56^T (98.3% 16S rRNA gene sequence similarity) while group II (n = 4) showed Flavobacterium hydatis DSM 2063^T as its nearest neighbour (98.5–98.9% 16S rRNA gene sequence similarity). Despite high 16S rRNA gene sequence similarity, these two groups represented two distinct novel species as shown by phenotypic traits and low genomic relatedness assessed by rep-PCR fingerprinting, DNA-DNA hybridization and whole-genome sequencing. Common to representative strains of both groups were the presence of major menaquinone MK-6 and sym-homospermidine as the major polyamine. Common major fatty acids were C_15:0 iso, C_15:1 iso G, C_15:0 iso 3-OH, C_17:0 iso 3OH and Summed Feature 3 (C_16:1 ω7c/C_16:1 ω6c). Strain CCM 8828^T (group I) contained phosphatidylethanolamine, three unidentified lipids lacking a functional group, three unidentified aminolipids and single unidentified glycolipid in the polar lipid profile. Strain CCM 8825^T (group II) contained phosphatidylethanolamine, eight unidentified lipids lacking a functional group, three unidentified aminolipids and two unidentified glycolipids in the polar lipid profile. These characteristics corresponded to characteristics of the genus Flavobacterium. The obtained results showed that the analysed strains represent novel species of the genus Flavobacterium, for which the names Flavobacterium circumlabens sp. nov. (type strain CCM 8828^T = P5626^T = LMG 30617^T) and Flavobacterium cupreum sp. nov. (type strain CCM 8825^T = P2683^T = LMG 30614^T) are proposed.     

Bench-scale fermentation of Trichoderma viride on wastewater sludge: Rheology,lytic enzymes and biocontrol activity

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 10⁷ CFU mL⁻¹ at 96 h) was obtained at 30 g L⁻¹ suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L⁻¹ suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL⁻¹ at 30 g L⁻¹ suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L⁻¹ compared to 30 and 25 g L⁻¹. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, k_La at 35 g L⁻¹ did not increase in comparison to 30 g L⁻¹ due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.     

Culture medium improvement for Isaria fumosorosea submerged conidia production

Submerged conidia and blastospores of the entomopathogenic fungus Isaria fumosorosea are produced in several liquid culture media. However, yields and the ecological fitness of these propagules vary according to culture media composition. In most culture media, hyphae, blastospores and submerged conidia are white but we found that in some media they develop a brown pigmentation. A dark pigment was extracted from brown-pigmented propagules and analyzed by IR spectroscopy. Adsorption bands coincided to those characteristics of melanins.Hadamard's matrices were employed in order to increase submerged conidia yields and brown pigmentation of fungal propagules. Media containing 20–30 mg/l of FeSO₄·7H₂O and 6–12 mg/l of CuSO₄·5H₂O allowed reaching the highest pigmentation (9 in a hedonic scale). A maximal concentration of submerged conidia of 1.0 (±1.2) × 10¹² cell/l was achieved after 120 h of liquid culture in a improved culture medium, containing 25 ml/l of Polyethylene glycol (MW 200), substance which enhanced submerged conidia production, reducing free mycelia or mycelial pellets formation. In the improved medium, it was estimated that more than 60% of produced biomass corresponded to submerged conidia and blastospores, while in other media, mycelia were the main product (80–97%).     

Microencapsulating aerial conidia of Trichoderma harzianum through spray drying at elevated temperatures

Conidia of Trichoderma harzianum produced from either solid or liquid fermentation must be dried to prevent spoilage by microbial contamination, and to induce dormancy for formulation development and prolonged self-life. Drying conidia of Trichoderma spp. in large scale production remains the major constraint because conidia lose viability during the drying process at elevated temperatures. Moreover, caking must be avoided during drying because heat generated by milling conidial chunks will kill conidia. It is ideal to dry conidia into a flow-able powder for further formulation development. A method was developed for microencapsulation of Trichoderma conidia with sugar through spray drying. Microencapsulation with sugars, such as sucrose, molasses or glycerol, significantly (P < 0.05) increased the survival percentages of conidia after drying. Microencapsulation of conidia with 2% sucrose solution resulted in the highest survival percentage when compared with other sucrose concentrations and had about 7.5 × 10¹⁰ cfu in each gram of dried conidia, and 3.4 mg of sucrose added to each gram of dried conidia. The optimal inlet/outlet temperature setting was 60/31 °C for spray drying and microencapsulation. The particle size of microencapsulated conidia balls ranged from 10 to 25 μm. The spray dried biomass of T. harzianum was a flow-able powder with over 99% conidia, which could be used in a variety of formulation developments from seed coatings to sprayable formulations.     

Isolation of a biphenyl-degrading bacterium,Achromobacter sp. BP3, and cloning of the bph gene cluster

A bacterial strain, BP3, capable of degrading biphenyl, was isolated from petroleum-contaminated soil. Strain BP3 was identified preliminarily as Achromobacter sp. based on its physiological and biochemical characteristics and 16S rRNA gene sequence analysis. Strain BP3 was able to degrade 50 mg l^?1 of biphenyl within 12 h. A 16.7-kb DNA fragment consisting of the entire bph cluster (bphRA1A2XA3A4BCKHJID) was obtained by normal PCR amplification and chromosome walking. Genes encoding integrase and transposon related genes were detected upstream and downstream of the bph cluster, respectively, which indicated that the bph cluster might locate on a big mobile genetic element (MGE).     

Frigoriglobus tundricola gen. nov., sp. nov., a psychrotolerant cellulolytic planctomycete of the family Gemmataceae from a littoral tundra wetland

Planctomycetes of the family Gemmataceae are characterized by large genome sizes and cosmopolitan distribution in freshwater and terrestrial environments but their ecological functions remain poorly understood. In this study, we characterized a novel representative of this family, strain PL17^T, which was isolated from a littoral tundra wetland and was capable of growth on xylan and cellulose. Cells of this isolate were represented by pink-pigmented spheres that multiplied by budding and occurred singly or in short chains and aggregates. Strain PL17^T was obligately aerobic, mildly acidophilic chemoorganotrophic bacterium, which displayed good tolerance of low temperatures. The major fatty acids were C_18:0, C_16:1ω5, and βOH-C_16:1; the major polar lipid was trimethylornithine. The genome of strain PL17^T consisted of a 9.83 Mb chromosome and a 24.69 kb plasmid. The G + C contents of the chromosomal and plasmid DNA were 67.4 and 62.3 mol%, respectively. Over 8900 potential protein-coding genes were identified in the genome including a putative cellulase that contains a domain from the GH5 family of glycoside hydrolases. The genome of strain PL17^T contained one linked and one unlinked rRNA operons with 16S rRNA gene sequences displaying 94.5% similarity to that in Gemmata obscuriglobus UQM2246^T. Based on the results of comparative phenotypic, chemotaxonomic and phylogenomic analyses, we propose to classify strain PL17^T (= CECT 9407^T = VKM B-3467^T) as representing a novel genus and species of the family Gemmataceae, Frigoriglobus tundricola gen. nov., sp. nov.     

Cometabolic degradation of dibenzofuran by Comamonas sp. MQ

In this study, strain MQ belonging to the genera Comamonas was used to cometabolically degrade dibenzofuran (DBF) with naphthalene, phenanthrene, benzene, toluene, biphenyl and nitrobenzene, respectively, for the first time. Strain MQ could cometabolically degrade DBF in the growing system using naphthalene as a substrate and the K_i value of strain MQ on naphthalene and DBF was 90.26 mg L^?1 and 68.34 mg L^?1, respectively. The degradation rate of DBF by naphthalene-cultivated strain MQ cells (0.080 mmol L^?1 h^?1) was 1.05, 1.11, 1.13, 1.18 and 1.27-fold higher than that cultivated by phenanthrene, benzene, toluene, biphenyl and nitrobenzene, respectively. Examination of metabolites indicated that naphthalene-cultivated strain MQ cells degraded DBF to 2-hydroxy-4-(3′-oxo-3′H-benzofuran-2′-yliden)but-2-enoic acid (HOBB) and subsequently to salicylic acid via the lateral dioxygenation and meta cleavage pathway. In contrast, biphenyl-cultivated strain MQ cells degraded DBF to monohydroxydibenzofuran through the lateral dioxygenation without meta cleavage pathway. These results suggested that strain MQ could be useful in the bioremediation of environments contaminated by heterocyclic compounds mixtures with polycyclic aromatic hydrocarbons.     

Biomechanics of invasive growth by Armillaria rhizomorphs

Rhizomorphs of wood-decay basidiomycetes are root-like structures produced by the coordinated growth of thousands of hyphae. Very little is known about their development nor the way that they penetrate soils and rotting wood. In this study, we applied techniques used in previous studies on hyphae to explore the mechanics of the invasive growth process in Armillaria gallica. Growth rate measurements were made in media with different gel strengths. The osmolyte composition of rhizomorph sap was determined spectroscopically and the forces exerted by growing tips were measured using a force transducer. Cultured rhizomorphs extended at much faster rates than unbundled hyphae (3.5 mm d⁻¹ versus 1.5 mm d⁻¹) and their growth accelerated in response to increased medium gel strength (to 7.4 mm d⁻¹). Measurements of rhizomorph osmolality provided a turgor pressure estimate of 760 kPa (7.5 atm.), and spectroscopic analysis showed that this pressure was generated by the accumulation of erythritol, mannitol, and KCl. Forces exerted by growing tips ranged from 1 to 6 mN, corresponding to pressures of 40–300 kPa (0.4–3.0 atm.). Pressures exerted by extending rhizomorphs are comparable to those produced by individual vegetative hyphae. This suggests that the mechanical behavior of hyphae is similar whether they grow as unbundled cells or aggregate to form macroscopic rhizomorphs.     

Alkaliphilus serpentinus sp. nov. and Alkaliphilus pronyensis sp. nov., two novel anaerobic alkaliphilic species isolated from the serpentinite-hosted Prony Bay Hydrothermal Field (New Caledonia)

Two novel anaerobic alkaliphilic strains, designated as LacT^T and LacV^T, were isolated from the Prony Bay Hydrothermal Field (PBHF, New Caledonia). Cells were motile, Gram-positive, terminal endospore-forming rods, displaying a straight to curved morphology during the exponential phase. Strains LacT^T and LacV^T were mesophilic (optimum 30 °C), moderately alkaliphilic (optimum pH 8.2 and 8.7, respectively) and halotolerant (optimum 2% and 2.5% NaCl, respectively). Both strains were able to ferment yeast extract, peptone and casamino acids, but only strain LacT^T could use sugars (glucose, maltose and sucrose). Both strains disproportionated crotonate into acetate and butyrate. Phylogenetic analysis revealed that strains LacT^T and LacV^T shared 96.4% 16S rRNA gene sequence identity and were most closely related to A. peptidifermentans Z-7036, A. namsaraevii X-07-2 and A. hydrothermalis FatMR1 (95.7%–96.3%). Their genome size was of 3.29 Mb for strain LacT^T and 3.06 Mb for strain LacV^T with a G + C content of 36.0 and 33.9 mol%, respectively. The ANI value between both strains was 73.2 %. Finally, strains LacT^T (=DSM 100337 = JCM 30643) and LacV^T (=DSM 100017 = JCM 30644) are proposed as two novel species of the genus Alkaliphilus, order Clostridiales, phylum Firmicutes, Alkaliphilus serpentinus sp. nov. and Alkaliphilus pronyensis sp. nov., respectively. The genomes of the three Alkaliphilus species isolated from PBHF were consistently detected in the PBHF chimney metagenomes, although at very low abundance, but not significantly in the metagenomes of other serpentinizing systems (marine or terrestrial) worldwide, suggesting they represent indigenous members of the PBHF microbial ecosystem.     

Efficacy assessment of antifungal metabolites from Chaetomium globosum No.05, a new biocontrol agent,against Setosphaeria turcica

Northern corn leaf blight (NCLB), an important and potentially destructive corn foliar disease, is caused by Setosphaeria turcica. The intent of this study was to evaluate antifungal metabolites from Chaetomium globosum (Cg) strain No.05 to suppress NCLB in maize. This strain significantly suppressed mycelial growth of numerous phytopathogenic fungi especially S. turcica on potato dextrose agar medium. The secondary metabolites of the strain inhibited mycelial growth and conidial germination of S. turcica. When co-inoculated at three droplets (5 μL/droplet) of conidial suspension (5 × 10⁴ conidia/mL) on each 8-cm-long detached leaf, 20% culture filtrates completely suppressed disease incidence of northern corn leaf blight. The application of the culture filtrates at 2 h post-inoculation (hpi) of S. turcica in greenhouse studies showed a 81.9% inhibition of NCLB on the seedlings, while culture filtrates applied before pathogen inoculation showed even higher rates of disease reduction. The application of the culture filtrates had no observed effects on the treated maize leaves or seedlings. Two active compounds, isolated from the extracts, were identified as chaetoglobosin A and chaetoglobosin C based on the spectroscopic analysis. Both in vitro and in planta bioassay experiments showed that chaetoglobosin A displayed potent biocontrol efficiency against S. turcica. To the best of our knowledge, this is the first report of the evaluation of the inhibitory effects of C. globosum and chaetoglobosin A against S. turcica both in vitro and on detached maize leaves.     

Evaluation of fluorescent pseudomonads for plant growth promotion,antifungal activity against Rhizoctonia solani on common bean,and biocontrol potential

Fluorescent pseudomonads are ubiquitous bacteria that are common inhabitants of the rhizosphere and are the most studied group within the genus Pseudomonas. Bacterial isolates (n = 103) from the rhizosphere of wheat and common bean were assessed as potential biocontrol agents in this study. Fungal inhibition tests were performed by a plate assay in which each isolate was tested directly for the production of hydrogen cyanide, protease, siderophore and cellulase. Production of DAPG was verified by using an analytical high performance liquid chromatography assay (HPLC). Plant growth promotion was assessed in phytochamber trials and biocontrol activity was evaluated in greenhouse trials. In all, 52 bacterial isolates with antifungal activity against Rhizoctonia solani were found. Of the 52 isolates, 41 were selected according to their high efficiency in in vitro antagonism, which was shown as inhibition zones in the dual-culture assay. Six of the 41 rhizobacteria, including isolates UTPF7, UTPF13, UTPF18, UTPF22, UTPF27 and strain CHA0 produced HCN. Production of protease enzyme was detected for all isolates excluding UTPF30 isolate. Although some stains appeared not to produce any compound with affinity for ferric iron, other isolates produced prolific amounts, creating a large zone of orange (up to 160 mm², i.e., UTPF16). Seventeen of 41 isolates of fluorescent pseudomonads including strain CHAO produced different amounts of DAPG ranging from 0.6 to 11.4 ng/10⁸ cfu. A total of 39 isolates induced statistically significant effects on plant growth compared with the non-treated control for at least one parameter. The predominant influence observed was increased root length. No bacteria could completely protect the plant against R. solani, although all isolates significantly increased fresh weight as compared to the infested control in greenhouse trials. Pseudomonas fluorescens isolates UTPF16 and UTPF26 significantly (P < 0.05) decreased the number of seedlings with damping-off symptoms in the means of the experiments.     

Assessment of germination and carnivorous activities of a nematode-trapping fungus Arthrobotrys dactyloides in fungistatic and fungicidal soil environment

Carnivorism is the ability of nematode-trapping fungi to trap and digest the nematodes by sophisticated devices called traps. Delivery of nematode-trapping fungi in soil for bio-control of pest nematodes often fails or gives inconsistent results. Possible reasons for failure could be the effect of soil fungistasis on germination of nematode-trapping fungi in soil environment, use of avirulent species and sensitivity of these fungi to fungicidal residues in soil. Exploitation of nematode-trapping fungi for nematode control demands that it be compatible with fungicides applied in soil or crops and proliferate in soil. This investigation represents is one of the first to evaluate the effect of fungicides on the nematode-trapping fungus Arthrobotrys dactyloides. A. dactyloides showed in vitro carnivorous potential against Meloidogyne incognita, Meloidogyne javanica, Meloidogyne graminicola, Helicotylenchus dihystera and Heterodera cajani. Conidia of A. dactyloides exposed to agricultural soils showed poor germination but formed conidial traps, which captured and killed the soil nematodes. Conidial traps, which trapped the nematodes, grew well in all soils after killing and nutrient absorption from nematode body. Soil amended with 20 mg ai kg⁻¹ of carbendazim and thiram, 30 mg ai kg⁻¹ of mancozeb, 50 mg ai kg⁻¹ of captan, and 100 mg ai kg⁻¹ of carboxin completely checked the conidial trap formation and nematode capturing. 30, 50 and 100 mg ai kg⁻¹ of metalaxyl adversely affected the conidial trap formation and nematode capturing in soil. Propiconazole inhibited 15.2% conidial trap formation up to 50 mg ai kg⁻¹ but caused 93.3% inhibition of conidial traps formation and complete inhibition of nematode capturing at 100 mg ai kg⁻¹. Sulphur, triademefon, and tricyclazole showed least toxic effect on conidial trap formation and nematode capturing activities of A. dactyloides in soil up to 100 mg ai kg⁻¹.