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One of the major obstacles of Bt production as a biopesticide is its expensive bioprocess and fermentation. Therefore, the objective of the present study was to optimize growth condition and develop a low-cost bioprocess for mass production of a native coleopteran-effective Bacillus thuringiensis (Bt) strain (KH4) based on agricultural wastes, at incubator and batch fermenter level. Preliminary experiments showed that the optimum pH and temperature for the strain were 6.5 and 30°C, respectively. The maximum growth and spore/crystal production were observed in the medium containing 2% molasses and 3% corn steep liquor as carbon and nitrogen sources, respectively. Different concentrations of the sea salt were used as a new cheap and available mineral source. Sea salt with final 0.003% w/w concentration showed the highest rate of growth for the strain. The experiments in Batch fermenter showed that volume of 2% bacterial inoculation in total volume of medium culture was the best concentration as preculture. It was shown that pH significantly decreased at the beginning of logarithmic phase, whereas it significantly increased at the end of the logarithmic phase. By increasing fermentation period, the oxygen demand was increased, and by increasing oxygen concentration up to 70%, the bacterial growth and the spores/crystal production was increased. Based on the results, the growth condition of the strain was optimized and a new cheap and available commercial fermentation medium was developed for mass production of the strain in the batch systems.

Keywords: Agricultural waste, Bt, Economical growth media, Fermentation

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