Maureen S. Wright

Effects of volatile aldehydes from Aspergillus-resistant varieties of corn on Aspergillus parasiticus growth and aflatoxin biosynthesis

The fungi Aspergillus flavus and Aspergillus parasiticus produce a potent class of hepatocarcinogens known as aflatoxins. Corn-derived volatile compounds have been previously found to affect growth and aflatoxin production in A. flavus. In this study, the effects on A. parasiticus of three corn-derived volatile compounds, n-decyl aldehyde, hexanal and octanal, were measured. These three compounds were previously found to be variably expressed in five Aspergillus-resistant maize strains and three susceptible strains. In this study, A. parasiticus radial growth was restricted least by n-decyl aldehyde and most by octanal. Treatments of 100 microl of both hexanal and octanal were found to completely inhibit radial growth of the fungus using an agar plate assay method. While the volatile compound n-decyl aldehyde had less of an effect on radial growth than the other volatiles, the n-decyl aldehyde treated colonies had a predominance of uniquely aerial hyphae. These colony structures were found to have more complex hyphae and significantly fewer conidiophores than the control and other aldehyde treatments. Furthermore, aflatoxin production by the fungus was reduced by n-decyl aldehyde and hexanal, but was stimulated by octanal. The results presented here indicate that all three volatile compounds reduce radial growth but only n-decyl aldehyde significantly inhibits aflatoxin biosynthesis in A. parasiticus.

The effects of selected cotton-leaf volatiles on growth, development and aflatoxin production of Aspergillus parasiticus

The fungi Aspergillus flavus and Aspergillus parasiticus produce the hepatocarcinogenic, secondary metabolites, aflatoxins, in cottonseed, corn, peanuts and treenuts. Results have shown that aflatoxigenic strains of A. flavus and A. parasiticus grown in the presence of specific cotton-leaf volatiles exhibit alterations in aflatoxin production accompanied by variations in growth of the fungi. In this study, two alcohols (3-methyl-1-butanol (3-MB) and nonanol) and two terpenes (camphene and limonene) were chosen as representative cotton-leaf volatiles based on the effects they had on fungal growth and/ or aflatoxin production in previous investigations. The morphological effects of volatile exposure were examined in correlation with fungal growth and aflatoxin production. 3-MB-treated samples exhibited a decrease in fungal radial growth which was directly proportional to the volatile dosage. Additionally, 3-MB treatment resulted in loss of mycelial pigmentation and a decrease in sporulation. Limonene and camphene-treated samples yielded negligible differences in radial growth and morphology when compared to unexposed controls. In addition to radial growth inhibition, samples grown in the presence of nonanol demonstrated uniquely aerial hyphae. In comparison to an unexposed control, aflatoxin production increased in cultures exposed to 3-MB but decreased when exposed to the other three volatiles studied.

A Strain of the Fungus Metarhizium anisopliae for Controlling Subterranean Termites

Alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki, collected after swarming in 2002 died within 48 h, and the cadavers were visibly infected with a fungus. Fungi were picked from the cadavers, transferred to media, and ultimately isolated to purity. The individual fungal cultures were then used to infect Formosan subterranean termite workers. A single fungal isolate, C4-B, taxonomically identified as Metarhizium anisopliae (Metschnikoff), was found to cause rapid mortality of Formosan subterranean termite alates. This is the first report of a biological control agent for termite alates. In initial experiments, C4-B was more lethal to both alates and workers compared with M. anisopliae strain ESC 1, previously marketed as the termite biocontrol agent BioBlast. Dose-response assays in which Formosan subterranean termite alates were exposed to a known concentration of C4-B spores revealed that 10(6) spores/microl killed 100% of the alates in 3 d, both 10(5) and 10(4) spores/microl in 6 d, 10(3) spores/microl in 9 d, and 10(0) spores/microl in 12 d. Assays with workers demonstrated that 10(6) and 10(5) spores/microl killed 100% of the workers in 6 d. In an experiment to test the transfer of inoculum from infected workers to uninfected nestmates, 62.8% of the workers died in 21 d when only 20% of the workers had been inoculated. Mortality of alates caused by C4-B was tested at two field sites by dispersing fungal spores on grassy lawns and collecting alates from the treated areas. Alates thus infected showed 100% mortality by day 5, whereas only 64.8% of untreated control alates from the same collection area were dead on that day.

Virulence of Bacteria Associated with the Formosan Subterranean Termite (Isoptera: Rhinotermitidae) in New Orleans, LA

Abstract Examination of Formosan subterranean termites, Coptotermes formosanus Shiraki, for possible biological control agents revealed the presence of 15 bacteria and one fungus associated with dead termites from New Orleans, LA, USA. All but one of the bacteria species were gram-negative bacteria. Bacterial isolates from dead termites were primarily Serratia marcescens Bizio that caused septicemia in C. formosanus and also appeared to contain proteolytic enzymes. Multiple strains of S. marcescens were isolated. Six of the eight strains of S. marcescens were red, probably not pathogenic in humans, and candidates as biological control agents for C. formosanus. Bacteria isolated from termite substrata included Corynebacterium urealyticum Pitcher, Acinetobacter calcoacet/baumannii/Gen2 (Beijerinck), S. marcescens, and Enterobacter gergoviae Brenner. Some of these bacteria are potential human pathogens. Forced exposure bioassays demonstrated that the T8 strain of S. marcescens killed 100% of C. formosanus by day 19.

Increased Mortality of Coptotermes formosanus (Isoptera: Rhinotermitidae) Exposed to Eicosanoid Biosynthesis Inhibitors and Serratia marcescens (Eubacteriales: Enterobacteriaceae)

Abstract The biological control of termites may be facilitated if their highly evolved immune systems can be suppressed. Eicosanoids are C20 polyunsaturated acids that are of widespread biochemical importance, including their role in protecting insects from bacterial infection. In laboratory experiments, the eicosanoid biosynthesis inhibitors dexamethasone, ibuprofen, and ibuprofen sodium salt were each provided along with a red-pigmented isolate of Serratia marcescens Bizio, a bacterial pathogen, to the Formosan subterranean termite, Coptotermes formosanus Shiraki, by means of treated filter paper. The increased mortality that resulted with dexamethasone and ibuprofen supported, but alone was insufficient to prove, the hypothesis that the termites’ immune systems were suppressed by these compounds, making the insects more vulnerable to infection by S. marcescens. This effect on mortality was noted only at 3.4 × 1010 colony-forming units per milliliter, a high treatment level. A significant amount of the infection and subsequent mortality may have resulted from direct contact with the bacterium and the remainder from its ingestion. Water-soluble ibuprofen sodium salt demonstrated a protective effect that was unexpected in light of the increased termite mortality observed with the relatively water insoluble, free acid form.

Stability and Use of Sweet Sorghum Bagasse

With sweet sorghum production and subsequent accumulation of bagasse on the rise, it is important to look for novel uses for its by-products. Bagasse, the solid fibrous product left after sweet sorghum stalks are crushed to remove juice, is partially reapplied to the field to enhance subsequent crops. The majority of bagasse remains largely underutilized because more is produced than can be practically applied to fields. This study determined sweet sorghum bagasse chemical and microbiological properties for use as a fuel source. It was determined that sweet sorghum variety had no major effect on fuel value. Microbes have the potential to consume sugars and other beneficial compounds in bagasse, but our analysis of microbial counts showed that microorganisms did not reduce the fuel value of the bagasse tested. Sweet sorghum bagasse was also found to have favorable fuel value when compared to sugarcane bagasse, due to its lower ash and higher fixed carbon contents.

Improved mortality of the Formosan subterranean termite by fungi, when amended with cuticle-degrading enzymes or eicosanoid biosynthesis inhibitors

Formosan subterranean termites (FST) were exposed to strains of Beauveria pseudobassiana (Bpb) and Isaria fumosorosea (Ifr) to determine virulence of the fungi. Once lethality was determined, sublethal doses of Bpb were combined with enzymes capable of degrading the insect cuticle to measure the potential to enhance fungal infection. Bpb applied to FST in combination with proteinases and a chitinase caused increased mortality over the fungus alone. Mortality was enhanced when Ifr was applied to FST in combination with a chitinase isolated from Serratia marcesans. A lipase isolated from Pseudomonas cepacia, when combined with Ifr, also resulted in greater mortality than all control treatments. FST were also exposed to the eicosanoid biosynthesis inhibitors (EBIs) dexamethasone (DEX), ibuprofen (IBU), and ibuprofen sodium salt (IBUNA), in combination with Ifr. Combining Ifr with IBUNA caused significantly increased mortality on days 6, 7, and 9. Cuticle-degrading enzymes and EBIs may have potential to enhance the pathogenic effect of a fungal control agent against the Formosan subterranean termite.

Microbial stability of worm castings and sugarcane filter mud compost blended with biochar

Abstract Organic amendments such as worm castings and sugarcane filter mud compost can provide nutrient rich substrates for enhanced plant growth. Physico-chemical and microbial stability of these substrates might be enhanced with the addition of biochar. A series of experiments was carried out to determine the stability of microbe populations in both worm castings and sugarcane filter mud compost with the addition of biochar made from sugarcane bagasse. Storage studies up to 150 days were carried out with biochar/worm castings and biochar/sugarcane filter mud compost blends on a volume basis (100/0; 90/10; 75/25; 50/50; 25/75; 10/90; 0/100). Physico-chemical properties, such as micro and macro nutrient composition, pH, ash and carbon contents, amongst others were monitored throughout storage time as well as microbe counts. No major deleterious effects to the microbial population were found by adding biochar to either substrate, despite decreasing moisture levels for increased biochar additions. Biochar might be providing nutrients needed by microbes, as well as possibly bind bacterial waste products that would otherwise be toxic to the microbe population. Larger scale studies are warranted as well as longer storage time to optimize shelf stability.