Recovery of Bacillus sphaericus spores by flocculation/sedimentation and flotation
The aim of this work was use flocculation/sedimentation and flotation for recovery of spores of the Bacillus sphaericus. Microorganism was produced batchwise using culture medium based skimmed milk, corn steep liquor and mineral salts. The best results of flocculation were obtained using CaCl2.2H2O, FeCl3.6H2O, Al2(SO4)3 and tannin as flocculating agents, with optimal flocculation concentrations of 1,500, 3,000, 2,000 and 1,700ppm, respectively. Flocculent suspensions were characterized based on floc diameter and density. Settling tests were performed in batch at different concentrations of the cellular suspensions and revealed high recovery of the solids in suspension in all cases. Flotation tests were accomplished using a mechanical agitated flotation cell and the process was favoured by the increase of the system agitation and for the presence of a cationic collector.
Binding of the 51- and 42-kDa individual components from the Bacillus sphaericus crystal toxin to mosquito larval midgut membranes from Culex and Anopheles sp. (Diptera: Culicidae).
Individual components (P51 and P42) from the crystal toxin (Bin) of Bacillus sphaericus were used for in vitro binding competition experiments with brush border membranes (BBMFs) from Culex pipiens and Anopheles gambiae larval midguts. P51 competed for the Bin binding site with a similar affinity to the Bin toxin, on both BBMFs. For C. pipiens, P42 bound non-specifically until P51 was added with maximum binding of P42 at a molar ratio of each component. The binding of P42 was much greater on A. gambiae BBMFs and the presence of either P51 or P42 enhanced the binding of the other component, with highest binding when a mole ratio of each protein was supplied.
Delineation of the minimal portion of the Bacillus sphaericus 1593M toxin required for the expression of larvicidal activity.
The two genes of Bacillus sphaericus 1953M coding for the 51.4-kDa and 41.9-kDa proteins are both required for the expression of the active larvicidal toxin in Escherichia coli. The minimal size of the active peptide of the 41.9-kDa toxin was defined by in vitro deletion analysis of the gene and found to consist of 338 amino acids (38.3 kDa). N-terminal deletions past the Ile18 residue and C-terminal deletions past the His352 residue result in the loss of toxic activity and rapid degradation of such modified toxins by host proteases. The minimal active 38.3-kDa peptide produced in E. coli seems to mimick the stable processed form of the toxin found in larval midguts. However, it still requires the action of the synergistic 51.4-kDa protein for the larvicidal activity.