Correction to: 'Antimicrobial defence and persistent infection in insects revisited'

Deciphering the molecular mechanisms of mother-to-egg immune protection in the mealworm beetle Tenebrio molitor

In a number of species, individuals exposed to pathogens can mount an immune response and transmit this immunological experience to their offspring, thereby protecting them against persistent threats. Such vertical transfer of immunity, named trans-generational immune priming (TGIP), has been described in both vertebrates and invertebrates. Although increasingly studied during the last decade, the mechanisms underlying TGIP in invertebrates are still elusive, especially those protecting the earliest offspring life stage, i.e. the embryo developing in the egg. In the present study, we combined different proteomic and transcriptomic approaches to determine whether mothers transfer a "signal" (such as fragments of infecting bacteria), mRNA and/or protein/peptide effectors to protect their eggs against two natural bacterial pathogens, namely the Gram-positive Bacillus thuringiensis and the Gram-negative Serratia entomophila. By taking the mealworm beetle Tenebrio molitor as a biological model, our results suggest that eggs are mainly protected by an active direct transfer of a restricted number of immune proteins and of antimicrobial peptides. In contrast, the present data do not support the involvement of mRNA transfer while the transmission of a "signal", if it happens, is marginal and only occurs within 24h after maternal exposure to bacteria. This work exemplifies how combining global approaches helps to disentangle the different scenarios of a complex trait, providing a comprehensive characterization of TGIP mechanisms in T. molitor. It also paves the way for future alike studies focusing on TGIP in a wide range of invertebrates and vertebrates to identify additional candidates that could be specific to TGIP and to investigate whether the TGIP mechanisms found herein are specific or common to all insect species.

Enzymatic, antimicrobial, and leishmanicidal bioactivity of gram-negative bacteria strains from the midgut of Lutzomyia evansi, an insect vector of leishmaniasis in Colombia

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The methanolic extract of Enterobacter hormaechei showed leishmanicidal activity against promastigotes of Leishmania braziliensis (strain UA301).

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P. ananatis, E. cloacae, A. gyllenbergii, O. anthropi and P. otitidis are promising bacteria in the biotechnology field as well as for biological control due to several enzymatic and antimicrobial bioactivities.

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Differential production of enzymes and secondary metabolites by Gram-negative bacteria could contribute to physiological and metabolic processes in the intestine of Lutzomyia evansi.

Knowledge regarding new compounds, peptides, and/or secondary metabolites secreted by bacteria isolated from the intestine of phebotominae has the potential to control insect vectors and pathogens (viruses, bacteria, and parasites) transmitted by them. In this respect, twelve Gram-negative bacteria isolated from the intestine of Lutzomyia evansi were selected and screened for their enzymatic, antimicrobial, and leishmanicidal activity. E. cancerogenus, E. aerogenes, P. otitidis, E. cloacae, L. soli, and P. ananatis exhibited enzymatic activity. 83.3% of the isolates displayed lipolytic and nitrate reductase activity and 58.3% of the isolates displayed protease activity. Hemolytic activity (17%) was identified only in E. hormaechei, and P. ananatis. E. cancerogenus, A. calcoaceticus, and P. otitidis showed cellulolytic activity. A. gyllenbergii, P. aeruginosa, and E. hormaechei showed amylolytic activity. In general, the totality of methanolic extracts exhibited antimicrobial activity, where E. hormaechei, A. calcoaceticus, and E. cancerogenus presented the highest activity against the evaluated reference bacteria strains. Cell-free supernatants (CFS_S) of the Gram-negative bacteria showed higher growth inhibitory activity against the reference Gram-positive bacteria. The CFS of A. gyllenbergii was the most active antimicrobial in this study, against S. aureus (AA_ODs = 95.12%) and E. faecalis (AA_ODs = 86.90%). The inhibition percentages of CFS against Gram-positive bacteria showed statistically significant differences (repeated measure ANOVA df= 2; F= 6.095; P= 0.007832). The E. hormaechei methanolic extract showed leishmanicidal activity (CE-50 μg/ml = 47.7 + 3.8) against metacyclic promastigotes of Leishmania braziliensis (UA301). Based on this finding, we discuss the possible implications of these bacteria in digestion and physiological processes in the Lu. evansi intestine. P. ananatis, E. cloacae, E. hormaechei, and P. otitidis were considered the most promising bacteria in this study and they could potentially be used for biological control.

Immune Defenses of a Beneficial Pest: The Mealworm Beetle, Tenebrio molitor

The mealworm beetle, Tenebrio molitor, is currently considered as a pest when infesting stored grains or grain products. However, mealworms are now being promoted as a beneficial insect because their high nutrient content makes them a viable food source and because they are capable of degrading polystyrene and plastic waste. These attributes make T. molitor attractive for mass rearing, which may promote disease transmission within the insect colonies. Disease resistance is of paramount importance for both the control and the culture of mealworms, and several biotic and abiotic environmental factors affect the success of their anti-parasitic defenses, both positively and negatively. After providing a detailed description of T. molitor’s anti-parasitic defenses, we review the main biotic and abiotic environmental factors that alter their presentation, and we discuss their implications for the purpose of controlling the development and health of this insect.