ABSTRACT
A Bacillus sphaericus strain 14N1 was isolated from Egyptian environments during the year 2002 that exhibited mosquitocidal activity higher than the international standard B. Sphaericus strain 2362. It was used for the production of mosquitocidal toxins using semisolid substrate fermentation [SSF] technology. This goal was achieved through a series of experimental studies aiming at the elucidation of the most important factors affecting growth parameters, CFU and spores counts and toxin production. These included sources of nutrients, type of carriers material, moisture content, aeration level, inoculum size, incubation period and response to additional nutritional supplements in terms of growth and sporulation parameters change and toxin productivity improvements. Among a group of finely ground agro-industrial by-products and legumes seeds used as substrates, the highest levels of toxins production were obtained using cotton seed meal, sesame seed meal followed by fodder yeast and linen seed meal. The optimum concentration of cottonseed meal in growth medium for mosquitocidal toxin production ranged between 3.0% and 6.0% [w/w]. The highly coarse wheat bran was the optimum carrier material for mosquitocidal toxin production followed by beat moss, kaoline clay mineral and talcum powder. The moisture content of semisolid medium exerted great influence on toxin production reaching maximum values at 50% [w/w] followed by progressive decrease at higher moisture contents reaching virtually no toxin production at 80% [w/w]. Within the tested inoculum size, the use of 19 x 106 CFU/g solid medium favored the toxin production. The level of toxin production was fairly stable within a wide range of increasing air space available in the experimental flasks except at very large levels of air space where a notable decline was noted in toxin production probably due to moisture loss of the culture. Progressive increase in toxin production was noted with extending incubation periods of culture reaching maximum toxin production level after nine days growth period followed by decline in toxin level upon extended incubation periods. Supplementation of growth medium with suitable concentration of peptone, yeast extract as well as with mineral salt solutions increased the production of toxin levels several folds. Lower increases in toxin production levels were obtained upon the addition of concentrates of corn steep liquor. The obtained results were discussed in the light of application feasibilities of mosquitocidal toxin production by SSF technology at lower and affordable expenses in the developing countries