Isolation of endophytic strains of Bacillus thuringiensis from wild plant seeds: A potential new biotechnological development

Abstract

Abstract In recent years, the insecticidal bacterium Bacillus thuringiensis has been found as an endophytic inhabitant of cultivated and wild plants. However, its ability to be vertically transmitted in nature is unknown. This work was aimed to detect B. thuringiensis strains within seeds of wild plants. Seeds were collected from nine different locations in northern and central Mexico, surface-sterilized and placed on LB agar for 18 h to corroborate sterilization. Then, seed were mashed, pasteurized, and inoculated in LB broth. Strains with B. thuringiensis morphology (ovoid spores and parasporal crystals) were isolated, and morphologically, molecularly, and toxicologically characterized. From seeds collected from 72 different plant species, 20 strains were isolated and identified as B. thuringiensis by their morphology, sequencing of the 16S ribosomal gene, the hag gene, and the MLST group of genes. Two isolates were identified as subspecies nigeriensis, two as israelensis, and one as thompsoni, while 15 were identified to species level. Parasporal bodies showed atypical morphology and no toxicity against Aedes aegypti larvae. One was highly toxic to Manduca sexta larvae and one more against Caenorhabditis elegans. Hence, B. thuringiensis was found in plant seeds at a high frequency (28%), potentially capable of vertical transmission in nature. The potential biotechnological significance of this discovery is discussed.