Evaluation of Beauveria bassiana (hyphomycetes) strains as potential agents for control of Triatoma infestans (Hemiptera: Reduviidae).

Chagas disease constitutes a major human health problem in most Latin American countries. This endemic disease is transmitted by several species of triatomine bugs, the most important being Triatoma infestans (Klug). In this article, we report on the selection of strains of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. virulent to T. infestans for possible use as bioinsecticides. Four strains of B. hassiana isolated from Argentina (Bb 1, 10, 25, and 65) were evaluated. To calculate mortality and mean lethal time, nymphs and adults of T. infestans were treated with conidia produced on complete agar medium and wheat brain and rice husk medium (WH). The LD50 for nymphs and adults of T. infestans was calculated. The effect of different temperatures (18, 22, 26, 30, and 34 degrees C) and relative humidities (35 and 90% RH) on mortality of nymphs were studied. We evaluated the compatibility of strains with Deltamethrin and Beta-Cypermethrin. Although the strain Bb 25 failed to grow on WH, the other three strains showed similar mortality values independent of the culture medium used to grow the microorganisms. The lowest LD50 values for nymphs were obtained with the strains Bb 10 and 65 and for adults were Bb 1, 10, and 65. The highest mean mortality was obtained with strain Bb 10, and among temperatures the highest mean mortality was observed at 26 degrees C. Relative humidity did not affect the mortality of T. infestans nymphs with all strains and temperatures assayed. Deltamethrin did not affect any of the three strains for the four studied doses, and Beta-Cypermethrin could be used in combination with the fungus only at low doses. The strain Bb 10 was selected for future assays under natural climatic conditions.

Organic and inorganic nitrogen source ratio effects onBacillus thuringiensis var.israelensis delta-endotoxin production.

The influence of different organic and inorganic nitrogen source combinations and C∶N ratios was studied in connection with growth and protein production ofBacillus thuringiensis var.israelensis. Protein production was assumed to be proportional to delta-endotoxin production. Delta-endotoxin concentration increased when media were supplemented with (NH4)2SO4, but the delta-endotoxin: biomass dry weight ratio was unaffected by different C∶N ratios. Organic nitrogen source, yeast extract, could be partially replaced by (NH4)2SO4 with a significant increase in delta-endotoxin production.

Effect of the media composition on the growth parameters and biological properties ofBacillus thuringiensis var.israelensis delta-endotoxin.

The effects of media composition on growth parameters, total protein production (including delta-endotoxin) and its relation to the biological properties ofBacillus thuringiensis var.israelensis was investigated. The replacement of glucose by glycerol as the carbon source yielded higher concentrations of delta-endotoxin. This increase in toxicity was associated with increased amounts of the 130 kDa polypeptide fraction. The biocide activity was not related to haemolytic activity. specific growth rate nor spore count.

[Influence of various ions in sporulation and the formation of delta-endotoxin in Bacillus thuringiensis cultures]. / Influencia de algunos iones en la esporulación y formación de delta-endotoxina en cultivos de Bacillus thuringiensis.

This paper deals with studies related to the influence of several ions on growth, spore formation and endotoxin formation by a Bacillus thuringiensis HD-1 strain commonly used for bioinsecticide production. Two basal media (4 and 5, Table 1) containing glucose, (NH4)2 SO4, phosphates and yeast extract or bacto peptone as organic nitrogen sources were supplemented with several ions in different concentrations, as shown in table 1. The experiments were conducted in 1000 ml Erlenmeyer flasks, containing 100 ml of medium, located in a rotary shaker at 30 degrees C. Several estimations were carried out, mainly biomass by optical density and colony forming units (CFU), glucose, Mg+2 and Mn+2 consumption and delta-endotoxin by a rocket immunoelectrophoretic method. The results obtained (Table 2) clearly show the importance of the addition of Ca+2, Mg+2 and Mn+2 to the basal media, because the highest values of CFU/l and delta-endotoxin (expressed as protein in g/l) were achieved in those media supplemented with the ions mentioned. It was also proved that the supplementation with Ca+2 was also essential for maintaining the thermal stability of the spores (Table 3). It can be concluded that an adequate formulation of media mainly related with the content of Mn+2, Mg+2 and Ca+2 is essential for obtaining high yields of spore crystal production of a Bacillus thuringiensis HD-1 strain.

Influencia de algunos iones en la esporulación y formación de delta-endotoxina en cultivos de Bacillus thuringiensis. / [Influence of various ions in sporulation and the formation of delta-endotoxin in Bacillus thuringiensis cultures]

This paper deals with studies related to the influence of several ions on growth, spore formation and endotoxin formation by a Bacillus thuringiensis HD-1 strain commonly used for bioinsecticide production. Two basal media (4 and 5, Table 1) containing glucose, (NH4)2 SO4, phosphates and yeast extract or bacto peptone as organic nitrogen sources were supplemented with several ions in different concentrations, as shown in table 1. The experiments were conducted in 1000 ml Erlenmeyer flasks, containing 100 ml of medium, located in a rotary shaker at 30 degrees C. Several estimations were carried out, mainly biomass by optical density and colony forming units (CFU), glucose, Mg+2 and Mn+2 consumption and delta-endotoxin by a rocket immunoelectrophoretic method. The results obtained (Table 2) clearly show the importance of the addition of Ca+2, Mg+2 and Mn+2 to the basal media, because the highest values of CFU/l and delta-endotoxin (expressed as protein in g/l) were achieved in those media supplemented with the ions mentioned. It was also proved that the supplementation with Ca+2 was also essential for maintaining the thermal stability of the spores (Table 3). It can be concluded that an adequate formulation of media mainly related with the content of Mn+2, Mg+2 and Ca+2 is essential for obtaining high yields of spore crystal production of a Bacillus thuringiensis HD-1 strain.