The insect pathogen Bacillus thuringiensis (Bt) holds great promise as an effective and friendly way for management of the pests with safety for nontarget animals and humans. However, high capital investment due to high production and formulation cost of commercial Bt preparations has caused prohibitive effect on companies. The present study mainly aimed at developing a low cost medium that supports the growth of different Bt strains and their specific bioinsecticidal &amp / #948 / -endotoxins (crystal proteins). A comparison was made between the representative members of three different subspecies of Bt to observe toxin yields in response to certain nutritional conditions. Three different Bt subspecies were Bt kurstaki (strain 81), Bt israelensis (strain HD500) and Bt tenebrionis (strain 3203), producing lepidoptera- and diptera-specific Cry1 and Cry2, diptera-specific Cry4Ba and Cry11Aa and coleoptera-specific Cry3Aa toxins, respectively. Studies were conducted to optimize glucose and inorganic phosphate concentrations in standard DSM medium for the production of these Bt-based biopesticides. General suppression of toxin yields in high glucose medium (10 g/L) thought the generality of carbon catabolite regulation for biosynthesis of different types of toxins. Inorganic phosphate (Pi) level was important for Cry4Ba, Cry11Aa and Cry3Aa biosynthesis while Cry1 and Cry2 production was not responsive to high Pi. Wastewater sludge, fruit residues and broiler litter were next tested as cheap raw materials for Bt-based biopesticide production in batch cultures. Broiler litter seemed to be a much better substrate among all since some degree of production of each toxin was observed at almost every stage of fermentation. The processing of broiler litter was found to significantly improve toxin yields. The medium prepared from processed broiler litter was successfully used to cultivate all Bt stains and obtain bioinsecticidal proteins in high yields which were comparable or higher than those that can be obtained on standard semi-synthetic media.

In the human gut, bacterial fermentation of dietary fibers and proteins produces metabolites, primarily as short-chain fatty acids (SCFA), that are highly beneficial for host health. However, unlike dietary fiber, bacterial fermentation of protein additionally generates potentially toxic substances such as ammonia, hydrogen sulfide, amines, and indoles. It is believed that most gut bacteria favor utilization of dietary fiber over that of protein for energy. Therefore, when fermentable dietary fiber is readily available to colonic bacteria, protein fermentation, and its subsequent potentially toxic metabolites, remains relatively low. Dietary intake primarily determines the quantity of dietary fiber and protein substrate available to the gut microbiota and the resulting profile of metabolites produced. Increased protein consumption is associated with deleterious health outcomes such as higher risk of colorectal cancer and type II diabetes. Conversely, diets following US dietary recommendations are high in fiber, which promote a healthy microbiome and are protective against disease. Diets following the recommendation are also moderate in protein intake so that, ultimately, far more fiber than protein is available for colonic bacterial fermentation. On the contrary, dietary fiber intake is chronically low in a standard Western diet, while protein consumption is above dietary recommendations, which results in nearly equal amounts of dietary fiber and protein available for gut microbial fermentation. Furthermore, the popularity of high-protein diets for athletes, as well as that of high-protein low-carbohydrate diets for weight loss, may flip fiber and protein substrate proportions upside down, resulting in more protein than fiber available in the gut for fermentation. The objective of this study was to elucidate how substrate ratios in protein-fiber mixtures affect protein fermentation and metabolites, as well as examine the degree to which fiber source may influence these outcomes. Each dietary fiber source [fructooligosaccharides (FOS), apple pectin (Pectin), a wheat bran and raw potato starch mixture (WB+PS), and an even mixture of the three aforementioned fibers (Even Mix)] and protein were combined in three ratios and provided as substrate for in vitro fecal fermentation to understand how low, medium, and high fiber inclusion levels influence fermentation outcomes. They were compared to 100% protein and fiber (each different fiber) controls. Branched-chain fatty acids (BCFAs), metabolites produced exclusively from protein fermentation, were used as a measure of protein fermentation; the data were normalized based on the initial quantity of protein within the substrate. In protein-fiber substrate mixtures, only FOS and Even Mix inhibited BCFAs (mM/g protein basis) and only when they made up at least half of the substrate. Unexpectedly, the rate of protein fermentation was increased when the protein-fiber substrate contained 25% WB+PS fiber, possibly due to the starch component of the fiber. There was evidence that when pH drops during fermentation, as was the case for protein-FOS mixtures, it played a significant role in suppressing protein fermentation. Ammonia production was not largely affected by increasing the proportion of dietary fiber. A significant reduction did not occur until FOS made up at least 50% of the protein-fiber substrate; for Pectin, WB+PS, and Even Mix fibers, 75% inclusion was required for a significant decrease in ammonia. Interestingly, protein was butyrogenic. Protein as the sole substrate produced more butyrate than either Pectin or Even Mix as the sole substrates, and in fact, addition of Pectin to protein significantly reduced butyrate concentrations. However, the possible benefits of butyrate produced via protein fermentation needs to be tempered by the production of potentially toxic compounds and the association between protein fermentation and colorectal cancer. Overall, the thesis findings showed protein fermentation to be relatively stable and not easily influenced by increasing the availability of dietary fiber, and no clear evidence of microbial preference for carbohydrates over protein was found.