Bacillus thuringiensis var. israelensis production involving re-use of the supernatant

Mosquito biolarvicide production by sequential fermentation with dual strains of Bacillus thuringiensis subsp. israelensis and Bacillus sphaericus using sewage sludge

This study demonstrated the bioconversion of sewage sludge into a composite biolarvicide for mosquito control based on sequential fermentation with dual strains of Bacillus thuringiensis subsp. israelensis (Bti) and Bacillus sphaericus (Bs). Results showed that sewage sludge was a suitable fermentation substrate for supporting growth, sporulation and mosquitocidal proteins synthesis by Bti and Bs. Through sequential fermentation with dual strains, a 10-L bench-scale fermentor was capable of producing Bti and Bs at a cell concentration of 2.1×10(9) and 6.8×10(8) CFU/mL, respectively. Such sequential fermentation can save half of raw materials and energy consumption comparing with the sludge fermentation with single strain. The toxic activity and persistence of the composite biolarvicide against mosquito larvae in the polluted waters were enhanced by the increased toxin complexity and synergistic interactions. This study, for the first time, validates the technical feasibility of using sewage sludge to produce a cost-effective composite biolarvicide based on Bti and Bs.

Greater enhancement of Bacillus subtilis spore yields in submerged cultures by optimization of medium composition through statistical experimental designs

Bacillus subtilis spore preparations are promising probiotics and biocontrol agents, which can be used in plants, animals, and humans. The aim of this work was to optimize the nutritional conditions using a statistical approach for the production of B. subtilis (WHK-Z12) spores. Our preliminary experiments show that corn starch, corn flour, and wheat bran were the best carbon sources. Using Plackett-Burman design, corn steep liquor, soybean flour, and yeast extract were found to be the best nitrogen source ingredients for enhancing spore production and were studied for further optimization using central composite design. The key medium components in our optimization medium were 16.18 g/l of corn steep liquor, 17.53 g/l of soybean flour, and 8.14 g/l of yeast extract. The improved medium produced spores as high as 1.52 +/- 0.06 x 10(10) spores/ml under flask cultivation conditions, and 1.56 +/- 0.07 x 10(10) spores/ml could be achieved in a 30-l fermenter after 40 h of cultivation. To the best of our knowledge, these results compared favorably to the documented spore yields produced by B. subtilis strains.

Coconut water as a cheap source for the production of delta endotoxin of Bacillus thuringiensis var. israelensis, a mosquito control agent

Bacillus thuringiensis var. israelensis (B. t. i.) is being widely used in mosquito control programs. However, the large-scale production of this bacillus is expensive due to the high cost of the production medium. In this study, we attempted to develop a cost-effective medium, based on a locally available raw material namely coconut water which is available in plenty as waste product from coconut oil industry. The yield of cell mass, sporulation and mosquito larvicidal activity were studied by growing this bacterium in this waste product and in comparison with the conventional medium (NYSM). Cell mass yield of 3.1g/L, spore count of 3.4x10(11)spores/mL and mosquito larvicidal activity (LC(50)) of 14.85ng/mL (against early fourth-instar larvae of Aedes aegypti) were obtained with a 30h old culture of this bacterium grown in coconut water. This is almost similar to that obtained with NYSM medium. Hence, coconut water-based culture medium is economical for the production of B. t. i.

Inorganic phosphate has a crucial effect on Cry3Aa delta-endotoxin production

AIMS

The study aimed at increasing Cry3Aa delta-endotoxin production by a local isolate of Bacillus thuringiensis (B.t. strain Mm2). To this end, different nutritional conditions were tested for their effects on Cry3Aa yields.

METHODS AND RESULTS

Bacillus thuringiensis Mm2 was grown by shaking at 30 degrees C in different media. Samples were taken from the cultures at intervals and used for protein extraction. SDS-PAGE was performed for toxin analysis. Inclusion of inorganic phosphate (Pi) into the Difco's sporulation medium at an increased level of 200 mmol l-1 caused a fivefold increase (from 3 to 15.6 microg ml-1) in toxin production. Omission of FeSO4 from the medium decreased this yield by half. Resuspension experiments suggested catabolite repression of toxin biosynthesis by glucose. The inclusion of high Pi invariably increased toxin synthesis, even in the absence of sugars.

CONCLUSIONS

Inorganic phosphate had the most striking effect on toxin biosynthesis. Iron effect was found to be unique to our isolate whereas Pi effect seemed to be common to the biosynthesis of Cry3Aa-type toxins. Stimulation of toxin synthesis by Pi did not seem to represent a relief from glucose repression.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacillus thuringiensis is the most versatile biopesticide for use in pest management. Regarding cost-effectiveness of related fermentations, high Pi supplement drastically increases Coleoptera-specific toxin synthesis.