Termiticidal activity of lectins from Myracrodruon urundeuva against Nasutitermes corniger and its mechanisms

The isolation of lectins from Myracrodruon urundeuva bark (MuBL) and heartwood (MuHL) as well as the termiticidal activity of MuHL against Nasutitermes corniger has already been described. This work reports on the purification of a leaf lectin (MuLL) and the characterization of MuBL, MuHL, and MuLL; also described are the resistance of hemagglutinating activity of the three lectins to trypsin activity from N. corniger gut and the termiticidal activity on N. corniger of MuBL (LC₅₀ of 0.974 mg ml⁻¹ on workers and 0.787 mg ml⁻¹ on soldiers) and MuLL (LC₅₀ of 0.374 mg ml⁻¹ on workers and 0.432 mg ml⁻¹ on soldiers). The antibacterial effect of MuBL, MuHL, and MuLL on bacteria from gut of N. corniger was also investigated and lectins showed similar bacteriostatic activity (MIC of 62.5 ??g ml⁻¹ for workers and 125 ??g ml⁻¹ for soldiers). MuBL and MuHL were more efficient bactericidal agents on bacteria in the workers’ gut (MBC of 125 ??g ml⁻¹) than MuLL (MBC of 250 ??g ml⁻¹) and similar bactericidal activity was detected on bacteria in the gut of soldiers (MBC of 250 ??g ml⁻¹). The termiticidal activity of M. urundeuva lectins can be explained by the chitin-binding property, resistance to termite digestive enzyme, and the antibacterial effect on symbiotic bacteria of N. corniger gut.     

A new Bauhinia monandra galactose-specific lectin purified in milligram quantities from secondary roots with antifungal and termiticidal activities

This work describes the purification in milligram quantities of a lectin from Bauhinia monandra secondary roots (BmoRoL) and its antifungal and termiticidal activities. The BmoRoL (6.2 mg) was isolated through ammonium sulfate fractionation and affinity chromatography on guar gel. Native lectin was resolved as a single band on polyacrylamide gel electrophoresis for basic proteins. Under denaturing and reducing conditions it appeared as a unique glycosylated polypeptide of 26 kDa. The highest agglutination activity of BmoRoL was found with glutaraldehyde-treated rabbit erythrocytes. BmoRoL showed antifungal activity against phytopathogenic species of Fusarium and was more active on Fusarium solani. The lectin also showed termiticidal activity on Nasutitermes corniger workers and soldiers with LC₅₀ of 0.09 and 0.395 mg ml⁻¹ for 12 days. In conclusion, BmoRoL is a new antifungal and termiticidal lectin that can be purified in milligram quantities and has potential biotechnological application for control of agricultural pests.     

Purified Cladonia verticillaris lichen lectin: Insecticidal activity on Nasutitermes corniger (Isoptera: Termitidae)

Cladonia verticillaris lichen lectin (ClaveLL) was isolated through Sephadex G-100 gel filtration chromatography and characterized as a pure lectin through ÄKTA-FPLC and HPLC systems. The lichen extract (LE), protein fraction (F₁) and ClaveLL were assayed to evaluate their potential insecticidal and/or repellence activities on termite Nasutitermes corniger. LE, F₁ and ClaveLL were evaluated for hemagglutinating activity (HA), protein concentration and presence of secondary metabolites; preparations and active ClaveLL, free of secondary metabolites, were able to induce termite mortality. ClaveLL LC₅₀ values after 10 days for workers and soldiers were 0.196 and 0.5 mg ml^?1, respectively. C. verticillaris preparations are potential tools for researches involving control of termites (or other insects) of economic interest to wooden industry or agriculture as well as preservation of plant species that are targets of termites or other plagues.     

Karlotoxin mediates grazing by Oxyrrhis marina on strains of Karlodinium veneficum

Karlodinium veneficum is a common member of temperate, coastal phytoplankton assemblages that occasionally forms blooms associated with fish kills. Here, we tested the hypothesis that the cytotoxic and ichthyotoxic compounds produced by K. veneficum, karlotoxins, can have anti-grazing properties against the heterotrophic dinoflagellate, Oxyrrhis marina. The sterol composition of O. marina (>80% cholesterol) renders it sensitive to karlotoxin, and does not vary substantially when fed different algal diets even for prey that are resistant to karlotoxin. At in situ bloom concentrations (10⁴–10⁵ K. veneficum ml⁻¹), grazing rates (cells ingested per Oxyrrhis h⁻¹) on toxic K. veneficum strain CCMP 2064 were 55% that observed on the non-toxic K. veneficum strain MD5. At lower prey concentrations typical of in situ non-bloom levels (<10³ cells ml⁻¹), grazing rates (cells ingested per Oxyrrhis h⁻¹) on toxic K. veneficum strain CCMP 2064 were 70–80% of rates on non-toxic strain MD5. Growth of O. marina was significantly suppressed when fed the toxic strain of K. veneficum. Experiments with mixed prey cultures, where non-toxic strain MD5 was fluorescently stained, showed that the presence of toxic strain CCMP 2064 inhibited grazing of O. marina on the co-occurring non-toxic strain MD5. Exogenous addition of a sub-lethal dose (100 ng ml⁻¹) of purified karlotoxin inhibited grazing of O. marina by approximately 50% on the non-toxic K. veneficum strain MD5 or the cryptophyte S. major. These results identify karlotoxin as an anti-grazing compound for those grazers with appropriate sterol composition (i.e., desmethyl sterols). This strategy is likely to be an important mechanism whereby growth of K. veneficum is uncoupled from losses due to grazing, allowing it to form ichthyotoxic blooms in situ.     

The effect of blueberry extracts on Giardia duodenalis viability and spontaneous excystation of Cryptosporidium parvum oocysts, in vitro

The protozoan parasites Giardia duodenalis and Cryptosporidium parvum are common causes of diarrhoea, worldwide. Effective drug treatment is available for G. duodenalis, but with anecdotal evidence of resistance or reduced compliance. There is no effective specific chemotherapeutic intervention for Cryptosporidium. Recently, there has been renewed interest in the antimicrobial properties of berries and their phenolic compounds but little work has been done on their antiparasitic actions. The effect of various preparations of blueberry (Vaccinium myrtillus) extract on G. duodenalis trophozoites and C. parvum oocysts were investigated. Pressed blueberry extract, a polyphenolic-rich blueberry extract, and a commercially produced blueberry drink (Bouvrage) all demonstrated antigiardial activity. The polyphenol-rich blueberry extract reduced trophozoite viability in a dose dependent manner. At 167 μg ml⁻¹, this extract performed as well as all dilutions of pressed blueberry extract and the Bouvrage beverage (9.6 ± 2.8% live trophozoites remaining after 24 h incubation). The lowest dilution of blueberry extract tested (12.5% v/v) contained >167 μg ml⁻¹ of polyphenolic compounds suggesting that polyphenols are responsible for the reduced survival of G. duodenalis trophozoites. The pressed blueberry extract, Bouvrage beverage and the polyphenolic-rich blueberry extract increased the spontaneous excystation of C. parvum oocysts at 37 °C, compared to controls, but only at a dilution of 50% Bouvrage beverage, equivalent to 213 μg ml⁻¹ gallic acid equivalents in the polyphenolic-rich blueberry extract. Above this level, spontaneous excystation is decreased. We conclude that water soluble extracts of blueberries can kill G. duodenalis trophozoites and modify the morphology of G. duodenalis and C. parvum.     

Behavioural Interactions Between <Emphasis Type="Italic">Crematogaster brevispinosa rochai</Emphasis> Forel (Hymenoptera: Formicidae) and Two <Emphasis Type="Italic">Nasutitermes</Emphasis> Species (Isoptera: Termitidae)

In the savanna-like Brazilian biome caatinga, the arboreal and polydomous ant Crematogaster brevispinosa rochai can be found cohabiting with two closely related Nasutitermes species (N. corniger and N. ephratae). This ant occupies variably sized portions of the termite nests and maintains a physical separation with its hosts by plugging the cells of the boundary areas with fibrous material. Although all the analysed cohabiting C. b. rochai nests were queenless, they always contained brood, especially from male and female reproductive castes. Interaction experiments between workers of C. b. rochai and workers or soldiers of N. ephratae revealed a low level of aggressiveness between the two species that contrasts with the aggressiveness of both C. b. rochai and N. ephratae in encounters with other ant (Azteca cf. chartifex, Cephalotes pusillus) or termite (M. cf. indistinctus) species. The association could benefit both ants (additional nesting sites, brood rearing places) and termites (protection against predators, dead ants or ant refuses as source of nitrogen).     

Algicidal activity of rhamnolipid biosurfactants produced by Pseudomonas aeruginosa

The algicidal activity of the rhamnolipid biosurfactants (the mixture of Rha-Rha-C₁₀-C₁₀ and Rha-C₁₀-C₁₀) produced by Pseudomonas aeruginosa was investigated in the present paper. The results indicated that the biosurfactants had potential algicidal effects on the harmful algal bloom (HAB) species, Heterosigma akashiwo. The growth of H. akashiwo was strongly inhibited in medium containing rhamnolipids (0.4–3.0 mg L⁻¹); moreover, the rhamnolipids showed strong lytic activity toward H. akashiwo at higher concentrations (≥4.0 mg L⁻¹). In addition, the effects of the rhamnolipids on the growth of Gymnodinium sp. and Prorocentrum dentatum, another two kinds of HAB species, were also studied. Compared with the dramatic algicidal effect on H. akashiwo, the cells of P. dentatum were inhibited or lysed at higher concentrations (1.0–10.0 mg L⁻¹), while the cells of Gymnodinium sp. were not suppressed with the same treatment, indicating the rhamnolipids had the potential for the selective control of HABs.Morphometric analysis at ultrastructural level by transmission electron micrographs indicated that the extent of ultrastructural damage of the alga was severe at high concentrations of rhamnolipids and during extended periods of contact. The first response occurred in the plasma membrane which partly disintegrated. The lack of membrane facilitated the rhamnolipid biosurfactants into the cells and allowed damage to other organelles, which resulted in the injury of chloroplast, vacuolization of mitochondria and deformation of the cristae, disruption of nuclear membrane and condensation of chromatin in nucleus, suggesting that the lytic activity of rhamnolipids was mainly due to their powerful surfactivity and their tendency to cohere on the surface of phospholipids bimolecular layer of the cells and further destroyed the layers, and then the structure of quasi-membrane configurations inside the cells was disintegrated, following by the irreversible damage to the ultrastructure and the loss of the function of organelles, consequently leading the cells to lyse.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.     

Control of the harmful alga Cochlodinium polykrikoides by the naked ciliate Strombidinopsis jeokjo in mesocosm enclosures

Red tides dominated by the harmful dinoflagellate Cochlodinium polykrikoides have caused annual losses of USD $5–60 million to the Korean aquaculture industry annually since 1995 and a loss of USD $3 million during a 1999 net-pen fish mortality event in Canada. In order to evaluate the potential to control C. polykrikoides red tides dominated by using mass-cultured heterotrophic protistan grazers, we monitored the abundance of Strombidinopsis jeokjo (a naked ciliate) and C. polykrikoides after mass-cultured S. jeokjo was introduced into mesocosms (ca. 60 l) deployed in situ and containing natural red tide waters dominated by C. polykrikoides. Water temperature, salinity, and pH, as well as the abundance of co-occurring other protists and metazooplankton were measured concurrently. To compare the growth and ingestion rates of S. jeokjo feeding on cultured versus natural populations of C. polykrikoides, we also monitored the abundance of cultured C. polykrikoides and S. jeokjo in bottles during laboratory grazing experiments. S. jeokjo introduced into the mesocosms grew well, effectively reducing natural populations of C. polykrikoides from approximately 1000 cells ml⁻¹ to below 10 cells ml⁻¹ within 2 days. The growth and ingestion rates of cultured S. jeokjo on natural populations of C. polykrikoides in the mesocosms for the first 30 h (0.72 day⁻¹ and 51 ng C grazer⁻¹ day⁻¹) were 84% and 44%, respectively, of those measured in the laboratory during bottle incubations with similar initial prey concentrations. The calculated grazing impact of S. jeokjo on natural populations of C. polykrikoides suggests that large-scale cultures of this ciliate could be used for controlling red tides by C. polykrikoides in small areas.     

The potential of Isaria spp. as a bioinsecticide for the biological control of Nasutitermes corniger

The termite Nasutitermes corniger is a serious pest infesting urban areas of Brazil and many other countries. Control largely depends on synthetic pesticides whose indiscriminate use can impact the environment and the health of humans and other animals. Alternative strategies against insect pests, such as biological control by entomopathogenic fungi, could be effective while minimising these deleterious effects. We analysed the actions of the entomopathogenic fungi Isaria farinosa, Isaria fumosorosea, and Isaria javanica against the insect N. corniger. Our results indicated that the fungi examined were pathogenic against N. corniger, with I. farinosa ESALQ1355 being the most efficacious strain, resulting in the death of 95% of the workers (LC₅₀ 6.66?×?10⁴ conidia/mL) and 85% of the soldiers (LC₅₀ 6.81?×?10⁴ conidia/mL). This is the first report of the pathogenicity of Isaria spp. on N. corniger. These in vitro results suggest that I. farinosa ESALQ1355 demonstrates a significant biological potential for controlling N. corniger.     

Production of microsclerotia of the fungal entomopathogen Metarhizium anisopliae and their potential for use as a biocontrol agent for soil-inhabiting insects

Microsclerotia (MS), overwintering structures produced by many plant pathogenic fungi, have not been described for Metarhizium anisopliae. Three strains of M. anisopliae – F52, TM109, and MA1200 – formed MS in shake flask cultures using media with varying carbon concentrations and carbon-to-nitrogen (C:N) ratios. Under the conditions of this study, all strains produced MS, compact hyphal aggregates that become pigmented with culture age, in addition to more typical blastospores and mycelia. While all strains formed desiccation tolerant MS, highest concentrations (2.7–2.9 × 10⁸ L⁻¹ liquid medium) were produced in rich media with C:N ratios of 30:1 and 50:1 by strain F52. All three strains of M. anisopliae produced similar biomass concentrations when media and growth time were compared. Strain MA1200 produced higher concentrations of blastospores than the other two strains of M. anisopliae with highest blastospore concentrations (1.6 and 4.2 × 10⁸ blastospores ml⁻¹ on days 4 and 8, respectively) in media with the highest carbon and nitrogen concentrations. Microsclerotial preparations of M. anisopliae containing diatomaceous earth survived air-drying (to <5 % moisture) with no significant loss in viability. Rehydration and incubation of air-dried MS granules on water agar plates resulted in hyphal germination and sporogenic germination to produce high concentrations of conidia. Bioassays using soil-incorporated, air-dried MS preparations resulted in significant infection and mortality in larvae of the sugar beet root maggot, Tetanops myopaeformis. This is the first report of the production of sclerotial bodies by M. anisopliae and provides a novel approach for the control of soil-dwelling insects with this entomopathogenic fungus.     

Nitrogen fixation in termites: Fate of newly fixed nitrogen

Nitrogen (¹⁵N) fixed by gut symbionts of the termite Nasutitermes corniger is assimilated and incorporated into termite tissues. Metabolic differences between soldier and worker castes are reflected in assimilation patterns: a greater proportion of the newly fixed nitrogen was in the bodies of workers but in the heads of soldiers. Newly fixed nitrogen is also transferred between workers and soldiers by trophallaxis. These studies confirm the 3:1 ratio assumed as the affinity of nitrogenase for acetylene relative to nitrogen in the acetylene-reduction method.     

Antioxidant,Fusarium growth inhibition and Nasutitermes corniger repellent activities of secondary metabolites from Myracrodruon urundeuva heartwood

Myracrodruon urundeuva heartwood is resistant to biodeterioration and lectin purified from heartwood showed antifungal and termiticidal activities. This report deals with antioxidant, antifungal and termite repellent activities of secondary metabolites from M. urundeuva heartwood. Saline (SE, active hemagglutinin preparation) and methanolic (ME, without hemagglutinating activity) extracts contain phenolic compounds, gallic acid, flavonoids, luteolin, cinamic derivatives, proanthocyanidins, hydrolysable tannins, and leucoanthocyanidins. Both SE and ME showed antioxidant activity and were effective in Fusarium growth inhibition. SE was efficient against Fusarium decemcellulare, Fusarium moniliforme, Fusarium oxysporum, and Fusarium solani but it had little effect against Fusarium lateritium. ME practically had no effect on F. decemcellulare and was more active than SE against F. lateritium. SE induced mortality of Nasutitermes corniger (LC₅₀ of 1.81 mg ml^?1 for soldiers and 2.59 mg ml^?1 for workers) and had no repellent activity. ME had no termiticidal activity but was a good repellent. The detected bioactivities point out the possibility of participation of secondary metabolites in the resistance of M. urundeuva heartwood to biodeterioration. Additionally, the results indicate the use of wood residues, as extracts, a source of natural bioactive agents.     

Monoclonal antibodies for the detection of Puccinia striiformis urediniospores

The fungal pathogen Pst causes yellow rust disease in wheat plants leading to crop losses. The organism spreads by releasing wind-dispersed urediniospores from infected plants. In this study a library of novel monoclonal antibodies (mAbs) was developed against Pst urediniospores. Nine mAb-producing cell lines were cloned and their cross-reactivities characterised against a panel of airborne fungal spores representing genera commonly found in the same environment as Pst. Two specific mAbs were used to develop a competitive ELISA (Pst mAb4) and a subtractive inhibition ELISA (Pst mAb8). Standard curves for both assays had good intra- and interday reproducibility. The subtractive inhibition ELISA had greater sensitivity with a detection limit of 1.5 × 10⁵ spores ml⁻¹. Cross-reactivity studies of Pst mAb8 in the subtractive inhibition ELISA, showed reaction with other Puccinia spores only, suggesting that common epitopes exist within this genus. The biosensor-compatible Pst mAb8 assay principle developed in this study has the potential to be implemented in future ‘label-free’ in-the-field systems for Pst detection.     

Surfactant aided biodegradation of pyrene using immobilized cells of Mycobacterium frederiksbergense

Low aqueous phase solubility is the major limiting factor in successful biodegradation of pyrene and other polycyclic aromatic hydrocarbons (PAH), which can, however, be overcome by using a suitable surfactant. Biodegradation of pyrene by immobilized cells of Mycobacterium frederiksbergense in presence of non-ionic surfactant Tween 80 was evaluated. For cell immobilization, beads were prepared using calcium alginate as the immobilizing material based on immobilized cell viability and mechanical stability of the beads. Complete degradation of pyrene was achieved employing the immobilized cells in batch shake flask experiments for all four different initial concentrations of the PAH at 100 mg l⁻¹, 200 mg l⁻¹, 400 mg l⁻¹ and 1000 mg l⁻¹. The experimental results of biodegradation of pyrene at very high initial concentration of 1000 mg l⁻¹ using the cell immobilized beads was further investigated in a 3 l fermentor operated at controlled conditions of 150 rpm, 28 °C, pH 7 and 1.5 l min⁻¹ aeration. The results confirmed complete degradation of the PAH with a very higher degradation rate of 250 mg l⁻¹ d⁻¹, which is so far the highest value reported for pyrene biodegradation.     

Effects of the estuarine dinoflagellate Pfiesteria shumwayae (Dinophyceae) on survival and grazing activity of several shellfish species

A series of experiments was conducted to examine effects of four strains of the estuarine dinoflagellate, Pfiesteria shumwayae, on the behavior and survival of larval and adult shellfish (bay scallop, Argopecten irradians; eastern oyster, Crassostrea virginica; northern quahogs, Mercenaria mercenaria; green mussels, Perna viridis [adults only]). In separate trials with larvae of A. irradians, C. virginica, and M. mercenaria, an aggressive predatory response of three strains of algal- and fish-fed P. shumwayae was observed (exception, algal-fed strain 1024C). Larval mortality resulted primarily from damage inflicted by physical attack of the flagellated cells, and secondarily from Pfiesteria toxin, as demonstrated in larval C. virginica exposed to P. shumwayae with versus without direct physical contact. Survival of adult shellfish and grazing activity depended upon the species and the cell density, strain, and nutritional history of P. shumwayae. No mortality of the four shellfish species was noted after 24 h of exposure to algal- or fish-fed P. shumwayae (strains 1024C, 1048C, and CCMP2089) in separate trials at ≤5 × 10³ cells ml⁻¹, whereas higher densities of fish-fed, but not algal-fed, populations (>7–8 × 10³ cells ml⁻¹) induced low (≤15%) but significant mortality. Adults of all four shellfish species sustained >90% mortality when exposed to fish-fed strain 270A1 (8 × 10³ cells ml⁻¹). In contrast, adult M. mercenaria and P. viridis exposed to a similar density of fish-fed strain 2172C sustained <15% mortality, and there was no mortality of A. irradians and C. virginica exposed to that strain. In mouse bioassays with tissue homogenates (adductor muscle, mantle, and whole animals) of A. irradians and M. mercenaria that had been exposed to P. shumwayae (three strains, separate trials), mice experienced several minutes of disorientation followed by recovery. Mice injected with tissue extracts from control animals fed cryptomonads showed no response. Grazing rates of adult shellfish on P. shumwayae (mean cell length ±1 standard error [S.E.], 9 ± 1 μm) generally were significantly lower when fed fish-fed (toxic) populations than when fed populations that previously had been maintained on algal prey, and grazing rates were highest with the nontoxic cryptomonad, Storeatula major (cell length 7 ± 1 μm). Abundant cysts of P. shumwayae were found in fecal strands of all shellfish species tested, and ≤45% of the feces produced viable flagellated cells when placed into favorable culture conditions. These findings were supported by a field study wherein fecal strands collected from field-collected adult shellfish (C. virginica, M. mercenaria, and ribbed mussels, Geukensia demissa) were confirmed to contain cysts of P. shumwayae, and these cysts produced fish-killing flagellated populations in standardized fish bioassays. Thus, predatory feeding by flagellated cells of P. shumwayae can adversely affect survival of larval bivalve molluscs, and grazing can be depressed when adult shellfish are fed P. shumwayae. The data suggest that P. shumwayae could affect recruitment of larval shellfish in estuaries and aquaculture facilities; shellfish can be adversely affected via reduced filtration rates; and adult shellfish may be vectors of toxic P. shumwayae when shellfish are transported from one geographic location to another.     

Reduction of cyanobacterial toxins through coprophagy in Mytilus edulis

An experiment was conducted to follow the fate of the cyanobacterial toxin, nodularin, produced by Nodularia spumigena through ingestion by Mytilus edulis and re-ingestion of faecal material (coprophagy). Mussels were fed with cultures of N. spumigena, and the faeces that were produced were fed to other mussels not previously exposed to N. spumigena. Concentrations of nodularin were measured in the food (N. spumigena), the mussels and in the faeces in order to make a toxin budget. High concentrations of nodularin were found in the mussels and their faeces after 48 h incubation with N. spumigena. When the toxic faeces were fed to new mussels, the toxin content of faeces was reduced from 95 μg nod g⁻¹ dry weight (DW) to 1 μg nod g⁻¹ DW through the process of coprophagy. Hence, when toxic faeces were fed to mussels, the nodularin concentration of the resulting faecal material was reduced by 99%. Pseudofaeces were produced when the mussels were grazing on N. spumigena, but not when grazing on faeces. The pseudofaeces contained high concentrations of nodularin and apparently intact N. spumigena cells. However, these cells were growth-inhibited and their potential contribution to seeding a bloom is probably limited. Our data indicate that a large fraction of ingested nodularin in M. edulis is egested with the faeces, and that the concentration of nodularin in the faeces is reduced when faeces are re-ingested.     

Kinetics of ammonium, nitrate and phosphorus uptake by Canna indica and Schoenoplectus validus

Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Löve and D. Löve is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C. indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (I_max) and Michaelis–Menten constant (K_m) were estimated by iterative curve fitting. The I_max for NH₄N (623 μmol g⁻¹ dry root weight h⁻¹) was significantly higher than that for NO₃N (338 μmol g⁻¹ dry root weight h⁻¹) in S. validus. In contrast, no difference was observed in C. indica. The I_max values for NO₃N and NH₄N were higher in S. validus than in C. indica. A significantly lower K_m was detected for NO₃N uptake in C. indica (385 μmol L⁻¹) compared to that in S. validus (1908 μmol L⁻¹). The I_max for PO₄P did not differ between the plant species. The K_m for PO₄P was significantly higher in C. indica (157 μmol L⁻¹) than in S. validus (60 μmol L⁻¹). In conclusion, we found that S. validus preferred NH₄N over NO₃N, had greater capacity for N uptake and higher affinity for PO₄P, but C. indica had greater affinity for NO₃N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes.     

The development and multiple uses of a standardised bioassay method to select hypocrealean fungi for biological control of aphids

A technically standardised bioassay method was designed, evaluated and used to assess virulence and host range of hypocrealean fungi against aphids. A track mounted sprayer was used to apply conidia because hand held versions of the same sprayer can be used for field applications, thereby allowing the outcome from laboratory experiments to predict activity in the field accurately. Eighteen fungal isolates were assessed in single concentration bioassays against the black bean aphid Aphis fabae Scopoli. Isolates comprised commercially available mycoinsecticides (based on Beauveria bassiana and Lecanicillium longisporum) and isolates of B. bassiana, Lecanicillium spp., Paecilomyces fumosoroseus and Metarhizium anisopliae. Aphid mortality was in excess of 80% for 15 isolates, and HRI 1.72 (L. longipsorum), Z11 (P. fumosoroseus), Mycotech strain GHA (B. bassiana) and ARSEF 2879 (B. bassiana) were studied further. Multiple concentration bioassays identified HRI 1.72 as the most virulent isolate against A. fabae with significantly smaller LC₅₀ and LT₅₀ values compared to other isolates. A precise LC₅₀ value (2.95 × 10² conidia ml⁻¹) was calculated for HRI 1.72 using a second multiple concentration assay with smaller concentrations of conidia. The four isolates were applied at a single concentration (1 × 10⁸ conidia ml⁻¹) against Myzus persicae, A. fabae, Acyrthosiphon pisum, Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi. A ranking of aphid susceptibility was obtained, such that S. avenae > M. persicae, A. pisum, A. fabae > R. padi. Results indicate the importance of standardising bioassay methods to reduce bioassay variability without compromising the ability to use the bioassay to investigate fungus–host interactions under varying abiotic and biotic conditions.     

Diet and physiological responses of Spondyliosoma cantharus (Linnaeus, 1758) to the Caulerpa racemosa var. cylindracea invasion

Marine invasions are a worldwide problem that involves changes in communities and the acclimation of organisms to them. The invasive Chlorophyte Caulerpa racemosa var. cylindracea is widespread in the Mediterranean and colonises large areas from 0 to 70 m in depth. The omnivorous fish Spondyliosoma cantharus presents a high frequency of occurrence of C. racemosa in the stomach contents at invaded areas (76.3%) while no presence of C. racemosa was detected in control areas. The isotopic composition of muscle differed significantly between invaded and non-invaded sites for δ¹³C (− 16.67‰ ± 0.09 and − 17.67‰ ± 0.08, respectively), δ¹⁵N (10.22‰ ± 0.22 and 9.32‰ ± 0.18, respectively) and the C:N ratio (2.01 ± 0.0002 and 1.96 ± 0.009, respectively). Despite the high frequency of occurrence of C. racemosa in the stomach contents of S. cantharus and its important contribution to the δ¹³C source (20.7% ± 16.2), the contribution of C. racemosa to the δ¹⁵N in S. cantharus food sources was very low (6.6% ± 5.8). Other invertebrate prey such as decapods and polychaetes were more important contributors to the δ¹⁵N source at both invaded and non-invaded sites. Activation of enzymatic pathways (catalase, superoxide dismutase, glutathione-s-tranferase, 7-ethoxy resorufin O-de-ethylase) but not a significant increase in lipid peroxidation MDA (0.49 ± 0.01 nmol/mg prot at non-invaded and 0.53 ± 0.01 nmol/mg prot at invaded sites) was observed in S. cantharus individuals living in C. racemosa-invaded sites compared with control specimens. The low δ¹⁵N contribution values of C. racemosa by S. cantharus together with the toxicity demonstrated by the activation of the antioxidant defences and the important contribution of invertebrate prey to the δ¹⁵N could mean that the ingestion of C. racemosa by S. cantharus might be unintentional during the predation of invertebrate preys living underneath the entanglement of the C. racemosa fronds and stolons mats.