During the last years, several applications of biosurfactants with medical purposes have been reported. Biosurfactants are considered relevant molecules for applications in combating many diseases. However, their use is currently extremely limited due to their high cost in relation to that of chemical surfactants. Use of inexpensive substrates can drastically decrease its production cost. Here, twelve solid substrates were screened for the production of Bacillus subtilis SPB1 biosurfactant and the maximum yield was found with millet. A Plackett-Burman design was then used to evaluate the effects of five variables (temperature, moisture, initial pH, inoculum age, and inoculum size). Statistical analyses showed that temperature, inoculum age, and moisture content had significantly positive effect on SPB1 biosurfactant production. Their values were further optimized using a central composite design and a response surface methodology. The optimal conditions of temperature, inoculum age, and moisture content obtained under the conditions of study were 37°C, 14 h, and 88%, respectively. The evaluation of the antimicrobial activity of this compound was carried out against 11 bacteria and 8 fungi. The results demonstrated that this biosurfactant exhibited an important antimicrobial activity against microorganisms with multidrug-resistant profiles. Its activity was very effective against Staphylococcus aureus, Staphylococcus xylosus, Enterococcus faecalis, Klebsiella pneumonia, and so forth.

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Vegetative insecticidal protein (Vip) is a class of insecticidal proteins produced by many Bacillus thuringiensis strains during their vegetative growth stage. The vip3LB gene of B. thuringiensis strain BUPM95, which encodes a protein active against the Lepidoptera olive tree pathogenic insect Prays oleae, was cloned into pET-14b vector and overexpressed in Escherichia coli. The expressed Vip3LB protein, found in the E. coli cytoplasmic fraction, was purified and used to produce anti-Vip3LB antibodies. Using the midgut extract of P. oleae, the purified Vip3LB bound to a 65-kDa protein, whereas Cry1Ac toxin bound to a 210-kDa midgut putative receptor. This result justifies the importance of the biological pest control agent Vip3LB that could be used as another alternative particularly in case of resistance to Cry toxins.

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A novel vip3-type gene named vip3LB has been isolated from Bacillus thuringiensis strain BUPM95. The corresponding secreted vegetative insecticidal protein was active against the lepidopteran insect Ephestia kuehniella. The vip3LB gene was shown, for the first time, to be carried by the large plasmid containing the cry1Ia genes of B. thuringiensis. The nucleotide sequence predicted a protein of 789 amino acids residues with a calculated molecular mass of 88.5kDa. Both nucleotide and amino acid sequences similarity analysis revealed that vip3LB is a new vip3-type gene, presenting several differences with the other vip3-type genes. Heterologous expression of the vip3LB under the control of the strong promoter P(BAD) was performed in Escherichia coli and the produced protein conferred insecticidal activity against Ephestia kuehniella. This novel vegetative insecticidal protein Vip3LB could be a very useful biological control agent.

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