Ultra-structural analysis of crystals produced by Bacillus thuringiensis INTA Fr7-4

DIEGO H. SAUKA; LAURA E. NAVAS; RUBÉN O. ZANDOMENI; GRACIELA B. BENINTENDE

Congreso; VIII Congreso de Microbiología General; 2012

Bacillus thuringiensis is a rod shape and gram-positive bacterium that produces parasporal proteinaceous insecticidal crystals during sporulation. Most strains produce proteins active against larvae of certain members of Lepidoptera. Fortunately, the isolation of new strains during the last decades has expanded the larvicidal activity against certain Diptera and Coleoptera species, increasing considerably the potential insecticidal applications of this bacterium. Bacillus thuringiensis INTA Fr7-4 is a native strain isolated from soil from Misiones Province. It is slightly toxic to the Coleoptera larva of Epilachna paenulata and Anthonomus grandis. There were no protein-coding genes that may be associated with this toxicity (cry3, cry7, cry8 and sip1A). This study presents an ultra-structural analysis of the crystals produced by this strain. Crystalline inclusions of INTA Fr7-4 were observed under phase contrast microscopy showing ovoid crystals. When ultra-thin sections of sporulating cells were analyzed under transmission electron microscopy, uniform ovoid crystals appeared, completely separated from the spores, and ranging in size from 0.7 to 0.8 mm. These dimensions were verified under scanning electron microscopy where, again, only ovoid crystals were observed. This morphology resembled to the parasporal crystals of the mosquitocidal B. thuringiensis serovar israelensis and to that produced by some Lepidoptera-toxic strains but not to typical Coleoptera-toxic strains.