Quantitative study of the phytoplankton of Lake Michigan at Evanston, Illinois

At this point, December 1939, two years of collecting have been completed and an attempt has been made to summarize and compare the data for that period

Intraspecific Aflatoxin Inhibition in Aspergillus flavus Is Thigmoregulated, Independent of Vegetative Compatibility Group and Is Strain Dependent

Biological control of preharvest aflatoxin contamination by atoxigenic stains of Aspergillus flavus has been demonstrated in several crops. The assumption is that some form of competition suppresses the fungus's ability to infect or produce aflatoxin when challenged. Intraspecific aflatoxin inhibition was demonstrated by others. This work investigates the mechanistic basis of that phenomenon. A toxigenic and atoxigenic isolate of A. flavus which exhibited intraspecific aflatoxin inhibition when grown together in suspended disc culture were not inhibited when grown in a filter insert-plate well system separated by a .4 or 3 µm membrane. Toxigenic and atoxigenic conidial mixtures (50∶50) placed on both sides of these filters restored inhibition. There was ∼50% inhibition when a 12 µm pore size filter was used. Conidial and mycelial diameters were in the 3.5–7.0 µm range and could pass through the 12 µm filter. Larger pore sizes in the initially separated system restored aflatoxin inhibition. This suggests isolates must come into physical contact with one another. This negates a role for nutrient competition or for soluble diffusible signals or antibiotics in aflatoxin inhibition. The toxigenic isolate was maximally sensitive to inhibition during the first 24 hrs of growth while the atoxigenic isolate was always inhibition competent. The atoxigenic isolate when grown with a green fluorescent protein (GFP) toxigenic isolate failed to inhibit aflatoxin indicating that there is specificity in the touch inhibiton. Several atoxigenic isolates were found which inhibited the GFP isolate. These results suggest that an unknown signaling pathway is initiated in the toxigenic isolate by physical interaction with an appropriate atoxigenic isolate in the first 24 hrs which prevents or down-regulates normal expression of aflatoxin after 3–5 days growth. We suspect thigmo-downregulation of aflatoxin synthesis is the mechanistic basis of intraspecific aflatoxin inhibition and the major contributor to biological control of aflatoxin contamination

Surface association and uptake of poly(lactic-co-glycolic) acid nanoparticles by Aspergillus flavus

AIM: To study the interaction of fluorescently tagged nanoparticles with Aspergillus flavus. MATERIALS & METHODS: Covalently tagged poly(lactic-co-glycolic) acid (PLGA) nanoparticles (PLGA-tetramethylrhodamine [PLGA-TRITC]), and PLGA-TRITC with entrapped coumarin-6 (double-tagged) nanoparticles, were synthesized using an oil-in-water emulsion evaporation method. Nanoparticle interaction with A. flavus was assessed using fluorescent microscopy. RESULTS: PLGA-TRITC nanoparticles associated with the surface of fungal spores and hyphae, with limited fluorescence observed within the interior. With double-tagged nanoparticles, comparatively more red fluorescence (TRITC) was measured on the fungal surface and more green (coumarin-6) on the interior, resulting from uptake of released coumarin-6. CONCLUSION: The majority of nanoparticles associated with the fungal surface, while smaller nanoparticles were internalized. Surface association between polymeric nanoparticles and A. flavus may facilitate content uptake

Surface association and uptake of poly(lactic-co-glycolic) acid nanoparticles by Aspergillus flavus

AIM: To study the interaction of fluorescently tagged nanoparticles with Aspergillus flavus. MATERIALS & METHODS: Covalently tagged poly(lactic-co-glycolic) acid (PLGA) nanoparticles (PLGA-tetramethylrhodamine [PLGA-TRITC]), and PLGA-TRITC with entrapped coumarin-6 (double-tagged) nanoparticles, were synthesized using an oil-in-water emulsion evaporation method. Nanoparticle interaction with A. flavus was assessed using fluorescent microscopy. RESULTS: PLGA-TRITC nanoparticles associated with the surface of fungal spores and hyphae, with limited fluorescence observed within the interior. With double-tagged nanoparticles, comparatively more red fluorescence (TRITC) was measured on the fungal surface and more green (coumarin-6) on the interior, resulting from uptake of released coumarin-6. CONCLUSION: The majority of nanoparticles associated with the fungal surface, while smaller nanoparticles were internalized. Surface association between polymeric nanoparticles and A. flavus may facilitate content uptake

Intraspecific aflatoxin inhibition.

<p>Aflatoxin B₁ production (ppb) in suspended disk culture by toxigenic isolate 53 growing with various atoxigenic isolates at 50∶50 or 80∶20 ratio of toxigenic to atoxigenic conidia.</p

Inhibition requires growing together.

<p>Aflatoxin B₁ production (ppb) in the filter insert-plate well system by toxigenic isolate 53 growing together with or separated from various atoxigenic isolates by a 0.4 µm pore size filter insert membrane.</p>1<p>Mix: Toxigenic 53 and atoxigenic isolates mixed together in and under filter.</p>2<p>T/A: Toxigenic 53 in filter and atoxigenic isolate under filter.</p>3<p>A/T: Atoxigenic isolate in filter and toxigenic 53 under filter.</p>4<p>Check: 53 in filter and only medium under filter.</p><p>*Means followed by the same letter are not significantly different at the α = 0.05 level.</p

Determining if soluble signal molecules are involved.

<p>Aflatoxin B₁ production in Spin-X centrifuge filter units (A). Tubes spun every 3 hrs for first 24 hrs and filtrates from tubes exchanged (1 and 2); or filtrates added back to itself (3 and 4) (B). Toxigenic isolate 53 and atoxigenic 51 were grown for a total of 5 days.</p

Effect of filter pore sizes on aflatoxin inhibition.

<p>Aflatoxin B₁ production by toxigenic isolate 53 in the filter insert-plate well system when grown together or separated from the atoxigenic isolate 51 by a range of filter insert membrane pore sizes.</p><p>*Means followed by the same letter are not significantly different at the α = 0.05 level.</p