Isolamento e caracterização molecular do Bacillus thuringiensis (Bt) (Bacillaceae), em solos sob cultivo orgânico

Abstract

Bacillus thuringiensis (Bt) is a Gram-positive, sporulating bacterium, characterized by presenting protein crystals in its structure. It has high toxicity to several orders of insects, which arouses the interest in researches in this sector in search of the control of pest species that affect agricultural and forestry production. The products under organic cultivation regime also already benefit from the results in the biological control of pests using commercial spores. In this context, studies in this sector assume the strategic role of promoting sustainable development in land use, with food quality and safety. With the objective of collecting data of publications on this bacterium, a scientific scientiometric analysis was carried out until April 2017, grouping them according to the language, country of publication, year and area of concentration of the researches. In a total of 14.098 articles were found. In the course of the study we can see that the country that most published articles on Bacillus thuringiensis was the USA, which is also a major agricultural producer worldwide, which justifies so much research in this area. Brazil was in ninth place in the ranking, between Mexico and Germany, but being the first in South America in publications. In addition, there has been a steady increase in publications involving this alternative method of pest control, especially since 1960. This decade stands out for the expansion of agricultural frontiers, the use of techniques and management of intensive agricultural production, and the indiscriminate use of agrochemicals. As a consequence, there were appearance of pests’ resistant to chemical formulas. This result clearly shows the growing awareness of the scientific community regarding the need for sustainability and reduction of agrochemicals released to the environment. Regarding the applied research during the months of April and May 2016, soil samples were collected in certified organic planting systems and Bt isolates. Subsequently, the presence of the cry1, cry2, cry3 and cry11 genes in the isolates was performed. The samples were obtained in the agricultural crop, Permanent Preservation Area (APP) and Legal Reserve (RL) of each property. For the morphological analyzes slides were prepared and observed in phase contrast microscopy (1000 ×), to verify the presence of bodies of parasporal inclusions (crystals). A positive result was observed in 17 samples. DNA extraction was performed by the boiling method, followed by agarose gel electrophoresis for DNA quantification ranging from 10ng to 40ng. For the amplification of the cry genes, preliminary tests were performed through polymerase chain reaction (PCR) followed by agarose gel electrophoresis. A satisfactory standard with annealing temperature at 50°C was obtained for the cry11 gene. The highest frequency of these isolates that presented the gene of interest was in Legal Reserve areas.