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Bacillus thuringiensis ssp. israelensis (Bti) is increasingly used as an ecologically friendly anti-mosquito agent. The bacterium cells undergo fermentation in dilute suspensions; before practical use, therefore it is necessary to concentrate the suspensions. Aggregation by polymers is a powerful tool with which to regulate the stability of suspensions. Typically, polymers at low concentrations destabilize and at high concentrations stabilize colloidal systems. Bti suspensions can be flocculated efficiently by either cationic or anionic polyelectrolytes. Cationic polyelectolytes were found to be the most efficient flocculants for bacterial suspensions. It was shown that the degree of toxicity of the flocculated Bti suspensions for biting mosquito larvae was in the same range than in non-flocculated suspension.

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The changes of cell surface hydrophilicity in Bacillus subtilis were analyzed in response to oxygen-limitation, heat shock, salt stress, pH-shock, phosphate- and carbon-limitation.  Although cell surface hydrophilicity varied during growth phases, an increase of surface hydrophilicity was observed under several of these stress conditions.  An observed drop in intracellular GTP and/or ATP may be an element of the signal transduction pathway leading to an increase in surface hydrophilicity in response to environmental stresses.  Attachment of cells to soil particles under salt stress conditions is strongly influenced by the degS/degU two-component system, which thereby provides a mechanism for the bacteria to escape from the hostile environment.

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