Surface characteristics of the entomopathogenic fungus Beauveria (Cordyceps) bassiana

Marked differences in surface characteristics were observed among three types of single-cell propagules produced by the entomopathogenic fungus Beauveria bassiana. Atomic force microscopy (AFM) revealed the presence of bundles or fascicles in aerial conidia absent from in vitro blastospores and submerged conidia. Contact angle measurements using polar and apolar test liquids placed on cell layers were used to calculate surface tension values and the free energies of interaction of the cell types with surfaces. These analyses indicated that the cell surfaces of aerial conidia were hydrophobic, whereas those of blastospores and submerged conidia were hydrophilic. Zeta potential determinations of the electrostatic charge distribution across the surface of the cells varied from +22 to -30 mV for 16-day aerial conidia at pH values ranging from 3 to 9, while the net surface charge ranged from +10 to -13 mV for submerged conidia, with much less variation observed for blastospores, +4 to -4 mV, over the same pH range. Measurements of hydrophobicity using microbial adhesion to hydrocarbons (MATH) indicated that the surfaces of aerial conidia were hydrophobic, and those of blastospores hydrophilic, whereas submerged conidia displayed cell surface characteristics on the borderline between hydrophobic and hydrophilic. Insect pathology assays using tobacco budworm (Heliothis virescens) larvae revealed some variation in virulence among aerial conidia, in vitro blastospores and submerged conidia, using both topical application and haemocoel injection of the fungal cells.

Phage display cDNA cloning and expression analysis of hydrophobins from the entomopathogenic fungus Beauveria (Cordyceps) bassiana

Hydrophobins are small amphipathic proteins that function in a broad range of growth and developmental processes in fungi. They are involved in the formation of aerial structures, the attachment of fungal cells to surfaces, and act in signalling in response to surface cues and pathogenesis. Beauveria bassiana is an important entomopathogenic fungus used as an arthropod biological control agent. To examine the feasibility of using phage display technology to clone cDNAs encoding hydrophobins, biopanning experiments were performed using a variety of affinity resins, including N,N'-diacetylchitobiose-, fucose-, lactose-, maltose- and melibiose-coupled agarose beads. After five rounds of iterative biopanning, cDNAs corresponding to two B. bassiana (class I) hydrophobins were selectively enriched using melibiose- or lactose-coupled agarose beads. Expression analysis revealed that the hyd1 gene was expressed in all samples tested, including aerial conidia, in vitro blastospores, submerged conidia, and cells sporulating on chitin and insect cuticle, with hyd1 expression peaking in growing mycelia. In contrast, the hyd2 gene was not appreciably expressed in any of the single-cell types (aerial conidia, blastospores and submerged conidia), but was constitutively expressed in growing mycelia and when cells were sporulating on chitin and insect cuticle. MS fingerprinting of an approximately 10 kDa protein found in boiling SDS-insoluble, trifluoroacetic acid-soluble extracts from aerial conidia identified the major component of the B. bassiana rodlet layer to be the hyd2 gene product. These results reveal the differential regulation of the isolated hydrophobins and indicate that phage display represents a novel approach to cDNA cloning of hydrophobins.

Oxalic acid as a fungal acaracidal virulence factor

Cell-free culture supernatants of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin were able to induce mortality in several tick species, including adult Ambylomma americanum (L.), Ambylomma maculatum Koch, and Ixodes scapularis Say. Four lines of experimental evidence support the hypothesis that oxalic acid secretion by B. bassiana, coupled to a reduction in the pH of the medium, act as potent acaricidal factors during pathogenesis. 1) Acaracidal activity of culture supernatants was retained after treatments including boiling and protease digestion, but was lost after dialysis. 2) Metabolite analyses indicated oxalate to be the major secreted organic compound present in the active culture supernatants. 3) Treatment of ticks with the pure compound oxalate at pH 4.0 resulted in almost 80% mortality in adult A. americanum ticks within 14 d, whereas treatment of ticks with oxalate at pH 7.0, or with formate, citrate, or phosphate at both pH 4 and 7 resulted in <10% mortality, even after 28 d. 4) Cell-free culture supernatants from B. bassiana mutants with decreased oxalate production displayed lower acaricide activity than wild type.

Pathogenicity of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae to Ixodidae tick species Dermacentor variabilis, Rhipicephalus sanguineus, and Ixodes scapularis

Nymphal and adult ticks from three different tick species, Dermacentor variabilis Say, Ixodes scapularis Say, and Rhipicephalus sanguineus Latrielle, were treated with conidia and blastospores of the entomopathogenic fungi Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae Metschnikoff. Dose-response experiments indicated that a critical concentration of fungal spores is required for infection and mortality. Over a 28-d time course, fungal suspensions of either B. bassiana or M. anisopliae at 10(8) conidia/ml resulted in 50-70% mortality in adult I. scapularis and R. sanguineus, but <20% mortality in D. variabilis ticks. R. sanguineus nymphs were highly susceptible to both entomopathogenic fungi, displaying >60% mortality within 14 d postinfection and >90% mortality within 21-28 d postinfection. D. variabilis nymphs also were more susceptible than their corresponding adults, displaying mortalities ranging from 20 to 40% 28 d postinfection. I. scapularis nymphs, however, seemed to be slightly less susceptible than adults (45% mortality, 28 d postinfection). The addition of nutrients to fungal cell suspensions did not have any noticeable effects on mortality toward any of the tick species tested. Significant mortality against D. variabilis adults (approximately 65%) was noted only when B. bassiana fungal cells with growth media carryover were used as the inoculum against the ticks. Entomopathogenic fungi such as B. bassiana and M. anisopliae may have the potential for controlling populations of I. scapularis and R. sanguineus, and under certain conditions D. variabilis. Our results indicate that inoculum conditions can greatly affect successful virulence and subsequent mortality.

Low-dose oral contraception and blood pressure in women with a past history of elevated blood pressure

Sixty-one women with a past history of elevated blood pressure (high-risk group) associated with oral contraceptive use (27 patients), unknown etiology (17 patients), or preeclampsia (17 patients) used a low-dose oral contraceptive containing 0.4 mg of norethindrone and 35 micrograms of ethinyl estradiol for 3 to 24 months. The highest blood pressures recorded in the past were 141.0 +/- 14.9 (mean +/- SD) mm Hg systolic and 98.3 +/- 8.0 diastolic. Sixty-one women without a past history of elevated blood pressure (low-risk group), selected from a pool of 616 low-risk patients, were matched with the high-risk group for race, initial age, initial body weight, duration of use, history of smoking, and family history of hypertension. The blood pressures in the high-risk group before and after oral contraceptive therapy were significantly higher than those in the low-risk group. Despite these differences, the mean systolic and diastolic blood pressures in these two groups of women using the low-dose oral contraceptive did not rise when compared with their own baseline blood pressures. Five high-risk patients (8.2%) discontinued therapy because of the redevelopment of hypertension; however, blood pressures at discontinuance were comparable to the previous highest blood pressures.