Abstract
Bacteria of the genus Bacillus can colonize endophytically and benefit several crops including the control of some pest orders. In view of the benefits provided by these microorganisms and in order to find out an efficient biotechnological control for the giant borer, our interest in studying the microorganisms in symbiosis with sugarcane and the giant borer has arisen, since there is no efficient chemical or biological control method for this pest. Therefore, endophytic Bacillus strains were isolated from three sugarcane niches (apoplast fluid, central internode cylinder and roots) and also from the giant borer larvae living inside sugarcane varieties grown in the Northeast region of Brazil. The taxonomical characterization (16S rRNA) of 157 Gram-positive isolates showed that 138 strains belonged to the Bacillus genus. The most representative species were phylogenetically closely related to B. megaterium (11.5%) followed by B. safensis (10.8%), B. cereus (8.9%), B. oleronius (8.9%), B. amyloliquefaciens (7.0%), and B. pacificus (6.4%). BOX-PCR analyses showed very distinct band pattern profiles suggesting a great diversity of Bacillus species within the sugarcane niches and the digestive tract, while the B. cereus group remained very closely clustered in the dendrogram. According to XRE biomarker analysis, eleven strains (FORCN005, 007, 008, 011, 012, 014, 067, 076, 092, 093, and 135) correspond to B. thuringiensis species. Additional studies using conserved genes (glp, gmk, pta, and tpi) indicated that most of these strains were phylogenetically closely related to B. thuringiensis and may be considered different subspecies. In conclusion, this study suggests that the culturable Bacillus species are greatly diversified within the plant niches and showed Bacillus species in the digestive tract of the giant borer for the first time. These results open new perspectives to understand the role and functions played by these microorganisms in symbiosis with this pest and also the possibility of developing an efficient biological control method for the giant borer using strains identified as the B. thuringiensis species.
Highlights
Endophytic bacteria are known to colonize, at some stage of their life cycle, internal tissues of the host plants without causing any visual pathogenic symptoms in plant cells (Azevedo et al, 2000; Hardoim et al, 2015)
Our study showed the presence of twelve closely related species including B. cereus, B. australimaris, B. safensis, B. nealsonii, B. aryabhattai, B. aerius, P. illinoisensis, P. barcinonensis, P. silvae, P. panacisoli, L. macroides, and L. fusiformis colonizing the digestive tract of giant borer lepidopteran larvae
Our results showed that the distinction of closely related Bacillus species such as B. thuringiensis and B. cereus is extremely difficult, being indicated to use more than one methodology
Summary
Endophytic bacteria are known to colonize, at some stage of their life cycle, internal tissues of the host plants without causing any visual pathogenic symptoms in plant cells (Azevedo et al, 2000; Hardoim et al, 2015). Endophytic microorganisms have shown antagonistic activity against several pathogenic bacteria and fungi (Lanna-Filho et al, 2017; Shahzad et al, 2017; Wang et al, 2019). Another important contribution of endophytic bacteria is their promising entomopathogenic potential, as has been demonstrated for the control of economically important pests (Bensidhoum et al, 2016; Schellenberger et al, 2016). Despite the great success of using B. thuringiensis, there are some disadvantages involved in the application of the available formulations (Sanahuja et al, 2011)
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