Optimization of medium as carbon and nitrogen sources for production of active ingredient of Bacillus thuringiensis bioinsecticide

anglais. An experiment was conducted to optimise media formulation for production of spore-crystal mixture (active ingredient of bioinsecticide) by Bacillus thuringiensis subsp. kurstaki (Bt). Molasses was used as carbon source at concentration of 1.0, 1.25, and 1.50 percent (w/v). The nitrogen sources used were soybean flour, yeast extract, and ammonium sulphate at concentration of 1.5 percent (w/v). Medium containing molasses 1.25 percent and yeast extract produced the highest Bt cell concentration. More than 90 percent of the Bt cells in the culture underwent lysis 48 hours after fermentation and released their spores and crystals into the medium. Medium containing combination of 1.5 percent mollases and yeast extract produced dry weights of spore crystal mixture (lyophilised in the presence of 26.48-g lactose) as much as 58.082 g/l. The highest value of VSC/mg dry weight (8.9 x 1010 VSC/mg dry weight of spore-crystal mixtures) was obtained in medium containing combination of 1.25 percent mollases and yeast extract. The highest level of the first instar larvae Crocidolomia binotalis (40.50 percent) mortality treated was obtained when the larvae was treated with the produced bioinsecticide from medium containing 1.5 percent mollases and ammonium sulphate

indonésien. Penelitian ini bertujuan untuk mengetahui kombinasi optimum antara konsentrasi molase sebagai sumber karbon dengan tepung kedelai, ekstrak khamir, dan amonium sulfat sebagai sumber nitrogen dalam medium fermentase untuk produksi bahan aktif bioinsektisida Bacillus thuringiensis (Bt) subsp kurstaki. Kombinasi karbon dan nitrogen yang optimal diperoleh pada medium yang mengandung ekstrak khamir dan molase 1,25 persen. Medium ini menghasilkan berat kering produk primer bioinsektisida tertinggi, yaitu 58,082 g/l (termasuk 26,48 g laktosa). Angka jumlah sel hidup (viable spore count, VSC) tertinggi diperoleh pada medium dengan kombinasi perlakuan molase 1,25 persen dan ekstrak khamir. Tingkat mortalitas tertinggi (40,05 persen) dari larva Crocidolomia binotalis yang digunakan untuk bioassay produk diperoleh dari perlakuan dengan produk yang dihasilkan dari medium yang mengandung molase 1,5 persen dan amonium sulfat