Nitrogen sources affect productivity, desiccation tolerance and storage stability of Beauveria bassiana blastospores.

AIMS: Nitrogen is a critical element in industrial fermentation media. This study investigated the influence of various nitrogen sources on blastospore production, desiccation tolerance and storage stability using two strains of the cosmopolitan insect-pathogenic fungus Beauveria bassiana. METHODS AND RESULTS: Complex organic sources of nitrogen such as soy flour, autolysed yeast and cottonseed flour induced great numbers of blastospores after 2-3 days of fermentation, which also survived drying and remained viable (32-56% survival) after 9 months storage at 4°C, although variations were found between strains. Nitrogen availability in the form of free amino acids directly influenced blastospore production and resistance to desiccation. Increasing glucose and nitrogen concentrations up to 120 and 30 g l-1 , respectively, did not improve blastospore production but enhanced desiccation tolerance. Cell viability after drying and upon fast-rehydration was increased when ≥25 g acid-hydrolysed casein per litre was supplemented in the liquid culture medium. CONCLUSIONS: These findings indicate that low-cost complex nitrogen compounds are suitable to enhance yeast-like growth by B. bassiana with good desiccation tolerance and therefore support its further scale-up production as a mycoinsecticide. SIGNIFICANCE AND IMPACT OF THE STUDY: Nitrogen is the most expensive nutrient in liquid media composition, but this study underscores the feasibility of using low-cost nitrogen compounds composed mainly of agro-industrial by-products for rapid production of desiccation-tolerant B. bassiana blastospores by liquid culture fermentation.

First record of epizootics in the ocola skipper, Panoquina ocola (Lepidopera: Hesperiidae), caused by Isaria tenuipes in flooded rice fields of Central Brazil.

AIMS: We report the first occurrence of an epizootic of the ascomycete fungus, Isaria tenuipes (teleomorph Cordyceps takaomontana), on the ocola skipper Panoquina ocola (Lepidoptera: Hesperiidae), an insect pest affecting rice in Brazil. METHODS AND RESULTS: Field surveys in flooded rice fields in the state of Goiás in Brazil were conducted, and a fungal pathogen of a caterpillar pest (P. ocola) was serendipitously found. This fungus inflicted high infection levels (average 86·2%) mainly to the pupal stage during warm, humid growing conditions. Typically, mycosed pupal cadavers produced milky-white to pale yellow synnemata bearing an average of 1·1 ± 0·2 × 109 conidia per cadaver. Based on phylogenetic analysis using beta-tubulin gene sequences, we confirmed that all 12 isolates obtained from field-mummified pupae were identifiable as I. tenuipes. CONCLUSIONS: Our data expand our knowledge on the host and geographical ranges of this mycopathogen and underscore its epizootic potential to affect a lepidopterous insect pest on rice in Brazil. This finding may facilitate the exploitation of this fungus as a mycoinsecticide. SIGNIFICANCE AND IMPACT OF THE STUDY: Isaria tenuipes may be used as an effective and environmentally friendly bioinsecticide against agricultural caterpillar pests due to its epizootic potential, as well as explored for medicinal purposes by pharmaceutical industry.

Nepetalactones from essential oil of Nepeta cataria represent a stable fly feeding and oviposition repellent.

The stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), is one of the most serious pests to livestock. It feeds mainly on cattle and causes significant economic losses in the cattle industry. Standard stable fly control involving insecticides and sanitation is usually costly and often has limited effectiveness. As we continue to evaluate and develop safer fly control strategies, the present study reports on the effectiveness of catnip (Nepeta cataria L.) oil and its constituent compounds, nepetalactones, as stable fly repellents. The essential oil of catnip reduced the feeding of stable flies by >96% in an in vitro bioassay system, compared with other sesquiterpene-rich plant oils (e.g. amyris and sandalwood). Catnip oil demonstrated strong repellency against stable flies relative to other chemicals for repelling biting insects, including isolongifolenone, 2-methylpiperidinyl-3-cyclohexen-1-carboxamide and (1S,2'S)-2-methylpiperidinyl-3-cyclohexen-1-carboxamide. The repellency against stable flies of the most commonly used mosquito repellent, DEET, was relatively low. In field trials, two formulations of catnip oil provided >95% protection and were effective for up to 6 h when tested on cattle. Catnip oil also acted as a strong oviposition repellent and reduced gravid stable fly oviposition by 98%.

Insight into the catalytic mechanism of DNA polymerase beta: structures of intermediate complexes.

The catalytic reaction mediated by DNA polymerases is known to require two Mg(II) ions, one associated with dNTP binding and the other involved in metal ion catalysis of the chemical step. Here we report a functional intermediate structure of a DNA polymerase with only one metal ion bound, the DNA polymerase beta-DNA template-primer-chromium(III).2'-deoxythymidine 5'-beta,gamma-methylenetriphosphate [Cr(III).dTMPPCP] complex, at 2.6 A resolution. The complex is distinct from the structures of other polymerase-DNA-ddNTP complexes in that the 3'-terminus of the primer has a free hydroxyl group. Hence, this structure represents a fully functional intermediate state. Support for this contention is provided by the observation of turnover in biochemical assays of crystallized protein as well as from the determination that soaking Pol beta crystals with Mn(II) ions leads to formation of the product complex, Pol beta-DNA-Cr(III).PCP, whose structure is also reported. An important feature of both structures is that the fingers subdomain is closed, similar to structures of other ternary complexes in which both metal ion sites are occupied. These results suggest that closing of the fingers subdomain is induced specifically by binding of the metal-dNTP complex prior to binding of the catalytic Mg(2+) ion. This has led us to reevaluate our previous evidence regarding the existence of a rate-limiting conformational change in Pol beta's reaction pathway. The results of stopped-flow studies suggest that there is no detectable rate-limiting conformational change step.

An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals.

The purpose of this study was to compare the canal length determined by an apex locator to the apical constriction in both vital and necrotic canals. Informed consent was obtained from patients waiting to have teeth extracted. The teeth were anesthetized, isolated, and accessed. The pulp was considered vital if bleeding was present in the pulp chamber. The Root ZX was used to measure the root canal length. The file was cemented into place, and the tooth was extracted. Twenty-nine teeth containing 34 cemented files were studied, and the distance from the apical constriction was measured. The Root ZX was 82.3% accurate to within 0.5 mm of the apical constriction. The mean distance from the apical constriction was 0.21 mm in vital cases versus 0.49 mm for necrotic cases. There was no statistical difference between the ability of the Root ZX to determine the apical constriction in vital canals versus necrotic canals.