Isolation of Beauveria bassiana from the Chagas Disease Vector Triatoma infestans in the Gran Chaco Region of Argentina: Assessment of Gene Expression during Host–Pathogen Interaction

Abstract

A native strain of the entomopathogenic fungus Beauveria bassiana (Bb-C001) was isolated from a naturally infected Triatoma infestans, Klug (Hemiptera: Reduviidae) adult cadaver in the Gran Chaco region, Salta province, Argentina. The isolate was both phenotypic and molecularly characterized in a context of fungus-insect interaction, by measuring the expression pattern of toxin genes during infection and immune response of T. infestans. The commercial strain GHA of B. bassiana, which was previously used in field interventions to control these vectors, was used as reference in this study. The phylogenetic trees based on both ribosomal internal transcribed spacer (ITS) and elongation factor 1-alpha (EF1-α) indicated that Bb-C001 fits into a B. bassiana cluster, and the sequence-characterized amplified regions (SCAR) showed that Bb-C001 is different from the GHA strain. There were no differences between both strains regarding viability, radial growth, and conidia production, either in the median survival time or insect mortality. However, Bb-C001 showed a higher expression than GHA of the bassianolide synthetase gene (BbbslS) during infection, and similar levels of the beauvericin synthetase gene (BbbeaS). Immune-related genes of T. infestans nymphs (limpet-2 and defensin-1, -2, and -6) were later expressed and thus insects failed to stop the infection process. These results showed that B. bassiana Bb-C001 is a promised fungal strain to be incorporated in the current biological control programs of T. infestans in Salta province, Argentina.

The Toxins of Beauveria bassiana and the Strategies to Improve Their Virulence to Insects

“…Notably, a study in Triatoma infestans showed that, compared with the third day of infection, many of the antimicrobial peptide and defensin genes were significantly inhibited on the ninth day of infection (Mannino et al, 2019). Although the regulatory mechanism was not confirmed, it was largely due to fungal toxins (Baldiviezo et al, 2020). These findings suggest that fungi which secreted secondary metabolites can resist the immune system of the hosts at both genetic and non-physiological levels, which sets up the basis for toxin(s) pathogenicity.…”

“…Among these, Metarhizium anisopliae, Beauveria bassiana, and Bacillus thuringiensis are the most effective biological control agents against mosquito vectors (Montalva et al, 2016). Apart from B. thuringiensis, B. bassiana is the most commonly used biopesticide that can be effectively transmitted (Baldiviezo et al, 2020).…”

Hexapod Assassins’ Potion: Venom Composition and Bioactivity from the Eurasian Assassin Bug Rhynocoris iracundus

“…In their natural environment, and especially during feeding, assassin bugs are exposed to various microorganisms. Insects can carry entomopathogens such as bacteria, fungi, and viruses [81,82] which could potentially affect and kill their predatory insects [83,84] via toxemia, bacteremia, or septicemia [85]. To analyze whether R. iracundus venom protects the assassin bug from potential pathogens, we tested its venom against Gram-positive and Gram-negative bacteria and found venom-mediated bacterial growth inhibition on Gram-negative E. coli only.…”

Host–Pathogen Interactions: Insects vs. Fungi

“…EPF interplay host defence with factors which regulate adhesion to the cuticle, cuticle degradation, stress management and toxins [5]. Thus B. bassiana express bassianolide and beauvericin toxins during infection of the bug Triatoma infestans [6] and proteases, chitinases and lipase in the presence of C. suppressalis cuticle probably to pass the insects defence faster [1]. It was found that EPF peroxisome-type and hexagonal crystal-like organelles (Woronin bodies) are required for appressorium differentiation and the topical infection of insect hosts [7].…”