Endophytic Bacillus Bacteria Living in Sugarcane Plant Tissues and Telchin licus licus Larvae (Drury) (Lepidoptera: Castniidae): The Symbiosis That May Open New Paths in the Biological Control

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.

Biosynthetic Mechanisms of Secondary Metabolites Promoted by the Interaction Between Endophytes and Plant Hosts

“…The endophytic alkaloid metabolites and neurotoxins may lead to disordered behavior, hindered growth and development, and even death of insects ( Song et al, 2020 ; Tooker and Giron, 2020 ; Grabka et al, 2022 ). For example, Bacillus in sugarcane can induce the abnormal development of giant borers, thus reducing diseases and insect pests ( Rocha et al, 2021 ).…”

Bacillus thuringiensis as a biofertilizer in crops and their implications in the control of phytopathogens and insect pests

“…Bt is ubiquitous in the soil but it is unclear whether it exists in the bulk soil in an active form or whether this is merely a ‘sump’ where spores are deposited for possible future consumption or distribution. The possible activity of Bt in the rhizosphere is also poorly studied with some indications that associations with roots may have a role in soil colonization 4–6 . Meanwhile, some studies have indicated that Bt may exist within plant tissues as a rhizospheric/endophytic bacterium, with implications for crop protection, as a bioprotectant and biofertilizer 7–9 …”

“…The possible activity of Bt in the rhizosphere is also poorly studied with some indications that associations with roots may have a role in soil colonization. [4][5][6] Meanwhile, some studies have indicated that Bt may exist within plant tissues as a rhizospheric/endophytic bacterium, with implications for crop protection, as a bioprotectant and biofertilizer. [7][8][9] Endophytic bacteria exist inside the plant tissues and this gives them an ability to contact with the plant's cells continually and to influence directly the plant host's metabolism.…”

Cultural Control of Giant Sugarcane Borer, Telchin licus (Lepidoptera: Castniidae), by Soil Mounding to Impede Adult Emergence

“…Some sugarcane genotypes seem to differ in pest incidence, but truly resistant varieties have not been identified (Dinardo-Miranda 2008). Bacterial sub-species of the Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) group have been isolated from the digestive tract of T. licus, suggesting the potential for using pathogenic strains of these bacteria against the pest (Rocha et al 2021), although this approach has not yet been adequately explored. Application of the entomopathogen Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) via sub-surface drip irrigation systems has proven relatively effective in controlling T. licus in trials in Brazil (Krontal 2014), but such irrigation systems are rarely used in Colombia.…”