The physiological effects of multi-walled carbon nanotubes (MWCNTs) on conidia and the development of the entomopathogenic fungus, Metarhizium anisopliae (Metsch.) Sorok.

The aim of the study was an in vitro evaluation of the effect of MWCNTs on the conidia of two strains of entomopathogenic fungus, Metarhizium anisopliae. The study made use of water suspensions of MWCNTs (concentration ∼ 3 mg·mL(-1)) made from commercial nanotubes and centrifuged. The conidia were placed in contact with nanotubes for 240 h. An assessment of MWCNT influence on conidia was performed after 1, 24, 72 and 240 h and focused on the linear growth of vegetative mycelium derived from these conidia, mycelium sporulation in subcultures and pathogenicity. Using TEM imaging, it was demonstrated that carbon nanotubes are able to damage cell membranes of the examined fungi conidia. However, the absence was noted of a significantly fungistatic effect of both MWCNT suspensions on the examined strains with respect to the physiological features in question. The increase in vegetative mycelium effected by spores after contact with MWCNTs was characterized by a slight modification in relation to the control. There was no strong trend (inhibition - stimulation), in relation to the effect of the tested suspension of carbon nanotubes, on the development of the vegetative mycelium in in vitro culture. Sporulation of the mycelium after completion of the culture only occurred in one case (strain Ma73F and culture of spores after 24-h contact with MWCNTs) significantly more intensely than in the controls. With respect to pathogenicity for test insects compared to the control strain, Ma73F spores grown from the longest contact with nanotubes suspensions performed significantly better. On the basis of the calculated of mycelium index growth rates and the time of death of the test insects (LT50), it was found that the adverse effects of water suspension MWCNTs on the spores of M. anisopliae were applied after a short contact with biological material. This indicates unfavorable physical rather than chemical effects on the tested cell. Over time, nanotube aggregation in water suspensions led to changes in their influence on the cells under examination.

Physiological aspects of the interaction of multi-walled carbon nanotubes with Beauveria bassiana (Balsamo) Vuillem in entomopathogenic spores.

The objective of the study was to evaluate the in vitro effect of aqueous suspensions of commercial multi-walled carbon nanotubes (MWCNTs) on spores of three entomopathogenic fungus species of Beauveria bassiana. Spores were placed in contact with MWCNTs for 1, 24, 72 and 216 h and then an in vitro evaluation in the subculture was performed on the linear growth of the vegetative mycelium of the spores after the contact with nanomaterial, as well as its sporulation after completion of the culture. No fungistatic effect of MWCNTs against B. bassiana spores was identified. Modification of vegetative mycelium surface growth in the culture of spores after contact with MWCNTs was mainly due to less effective inoculation, especially when shorter contact times with nanomaterial were applied. For one of the investigated strains, growth stimulation was observed in the culture of spores in contact with nanotubes for 72 and 216 h. Based on the significant intensification of sporulation observed in combination with the longest (216 h) contact with the investigated spore strains before culture with MWCNTs, it can be concluded that the tested nanomaterial constitutes a stress factor and may modify the metabolism of B. bassiana cells. Detailed evaluation of B. bassiana metabolic changes induced by MWCNTs should be conducted.

The effect of nanosilver on pigments production by Fusarium culmorum (W. G. Sm.) Sacc.

A disk-diffusion method experiment assessed the impact of nanosilver on production of secondary metabolites (pigments) by the Fusarium culmorum fungus. Nanosilver colloidal particles in water have been obtained by the use of a method based on high voltage electric arcs between silver electrodes. The silver nanoparticles size in colloid ranged between 15 and 100 nm and 7, 35 and 70 ppm concentration. Nanosilver modifies the metabolism of the researched F. culmorum strain. Coming into contact with nanosilver colloids induces more intensive mycelia pigmentation correlated with nanosilver concentration levels. The performed analysis of metabolites indicates that under the influence of nanosilver fungi biosynthesise aurofusarin more intensively and the conversion of rubrofusarin to aurofusarin is intensified as compared to the control culture. Under the influence of nanosilver F. culmorum intensively biosynthesises an unidentified dye which shares structural features with aurofusarin but which is not produced by fungi in standard cultures.

Physiological effect of multi-walled carbon nanotubes (MWCNTs) on conidia of the entomopathogenic fungus, Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes).

The aim of the investigation was to assess the influence of commercial and carboxylated multi-walled carbon nanotubes (MWCNTs) on conidia of the entomopathogenic fungus Paecilomyces fumosoroseus. The commercial MWCNTs had an external diameter of about 40-60 nm, a length of 300-600 nm, a specific density of 140 to 300 g/dm(3) and a carbon content of above 80%. Carboxylated MWCNTs were obtained by oxidizing commercial MWCNT by heating in HNO(3), filtering, washing with water and drying. Conidia after different times of contact (from 1 to 865 hours) with nanomaterials in aqueous solutions were cultured for linear and biomass growth. Growth and sporification of mycelium after culture were evaluated. MWCNTs are not greatly cytotoxic for P. fumosoroseus conidia in the applied concentrations. The linear growth of mycelium obtained from conidia after contact with nanotubes was inhibited only in 2 (out of 18) cases (ones for both kinds of nanotubes). Carboxylated nanotubes did not inhibit biomass growth at all, but commercial nanotubes inhibited biomass growth in 2 cases. Sporification was the feature most strongly modified by carbon nanotubes. The commercial nanotubes again more strongly limited sporification of mycelium than carboxylated nanotubes did. The relatively greater influence of commercial versus carboxylated nanotubes was observed in the experiments.