Comparative Evaluation of the Gut Microbiota Associated with the Below- and Above-Ground Life Stages (Larvae and Beetles) of the Forest Cockchafer, Melolontha hippocastani

Abstract

A comparison of the diversity of bacterial communities in the larval midgut and adult gut of the European forest cockchafer (Melolontha hippocastani) was carried out using approaches that were both dependent on and independent of cultivation. Clone libraries of the 16S rRNA gene revealed 150 operational taxonomic units (OTUs) that belong to 11 taxonomical classes and two other groups that could be classified only to the phylum level. The most abundant classes were β, δ and γ-proteobacteria, Clostridia, Bacilli, Erysipelotrichi and Sphingobacteria. Although the insect’s gut is emptied in the prepupal stage and the beetle undergoes a long diapause period, a subset of eight taxonomic classes from the aforementioned eleven were found to be common in the guts of diapausing adults and the larval midguts (L2, L3). Moreover, several bacterial phylotypes belonging to these common bacterial classes were found to be shared by the larval midgut and the adult gut. Despite this, the adult gut bacterial community represented a subset of that found in the larvae midgut. Consequently, the midgut of the larval instars contains a more diverse bacterial community compared to the adult gut. On the other hand, after the bacteria present in the larvae were cultivated, eight bacterial species were isolated. Moreover, we found evidence of the active role of some of the bacterial species isolated in food digestion, namely, the presence of amylase and xylanolytic properties. Finally, fluorescence in situ hybridization allowed us to confirm the presence of selected species in the insect gut and through this, their ecological niche as well as the metagenomic results. The results presented here elucidated the heterogeneity of aerobic and facultative bacteria in the gut of a holometabolous insect species having two different feeding habits.

The performance of Melolontha grubs on the roots of various plant species

“…Similar conclusions may be drawn from studies of M. melolontha grubs in which glucose concentration in the hindgut was found to be much lower than in the midgut (Egert et al, 2005). Xylanolytic bacteria were found in both the mid-and hindgut of M. hippocastani grubs, although their ability to degrade cellulose was not tested (Arias-Cordero et al, 2012). Generally, these results may indicate that structural carbohydrates, which are mostly concentrated in roots, are not as essential for the Melolontha grubs as nonstructural carbohydrates, which are present in significantly lower quantities.…”

Insect Gut Bacterial Diversity Determined by Environmental Habitat, Diet, Developmental Stage, and Phylogeny of Host

“…The microbiota of the insect gut has been analyzed using both culture-dependent (8)(9)(10) and culture-independent (11)(12)(13)(14)(15) methods. However, culture-dependent methods often produce biased results, depending upon the conditions and techniques used.…”

“…Comprehensive analysis of the bacterial diversity within a host species is a prerequisite in both insect physiology and microbial ecology to allow a better understanding of the ecological roles of insect symbionts and interactions with their insect hosts. However, most studies on gut bacterial diversity have been taxon specific, focusing on insects such as termites (10,17,18), ants (19)(20)(21), fire bugs (22)(23)(24), fruit flies (13,15,25), beetles (9,26,27), and bees (28)(29)(30)(31), leaving a need for broader and systematic characterization and comparison across all insects.…”

Antifungal activity of volatile compounds-producing Pseudomonas P2 strain against Rhizoctonia solani

“…The genus Pseudomonas which comprises many bacterial species exhibiting plant growth promoting effects has successfully been used as biocontrol agent (Arias-Cordero et al 2012). Many Pseudomonas bacteria are able to solubilise phosphate, to produce siderophore and to fix atmospheric nitrogen (do Carmo et al 2011).…”