Assessment of microbial communities associated with the gut and feeding substrate of three xylophagous coleopteran families with emphasis on cellulose-degrading bacteria
Guardado en:
| Autor: | |
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| Formato: | tesis de maestría |
| Fecha de Publicación: | 2019 |
| Descripción: | The current energy crisis and depletion of fossil fuel reserves has encouraged research for new alternatives. Degradation of plant material by enzymatic reactions represents an important strategy to obtain affordable and renewable energy. In nature, several beetle species have solved this problem by developing digestive systems colonized by specialized microbiota capable of breaking down recalcitrant carbon through cellulose- breaking enzymes, releasing sugars that later are used as nutrients. Therefore, their associated microbes represent potential sources of novel bioenergy-relevant molecules. Previous work, centered on one beetle Family (Passalidae) from one location in Costa Rica, revealed the occurrence of distinct microbial communities among larvae, adults and their woody substrate inside the same decomposing log. Furthermore, larval metagenomes were enriched in Firmicutes (particularly Ruminococcaceae) sequences and they harbor multiple genes coding for cellulose degrading enzymes. In the present study, I first evaluated whether the unique communities observed for Passalid beetles remain stable in other locations and compared them with other families of xylophagous beetles. This goal was achieved by sequencing 16S rRNA gene libraries from a total of 84 Coleopteran- associated samples collected in 3 different Costa Rican regions (Braulio Carrillo, Corcovado and Isla del Coco National Parks). These samples included the intestinal content of beetles (larvae and adults) belonging to 3 different families (Passalidae, Scarabaeidae and Cerambycidae) and the woody substrate they consume. Employing NMDS analyses, I confirmed that microbial communities are mainly driven by sample type (larvae, adult or substrate), but are also influenced by the other two variables: beetle family and geographic location. Also, I confirmed that Firmicutes is the most abundant phylum in both adult (40%) and larval (35%) samples from all beetles tested and that Ruminococcaceae (15%) is the most abundant family in larvae. The high abundance of Ruminococcaceae OTUs in larvae suggests an important role of these organisms in the overall gut metabolism and cellulose breakdown from the wood they feed on. To evaluate this possibility, available metagenomes and a collection of metagenome assembled genomes (MAGs) from Passalid beetles were employed to analyze the potential of the Ruminococcaceae family to degrade cellulose. From the metagenomes, 2-3% of all genes related to glycosil hydrolases (GHs) were assigned to the Ruminococcaceae family. Furthermore, out of the 11 Ruminococcaceae MAGs assembled in this work, 9 did not cluster with any of the reference genomes included in the analysis. Four of them have putative cellulases, while two of them, Bin 519 and 174, have gene clusters with several components related to cellulosomes. The present work suggests that anaerobic bacteria, such as Ruminococcaceae, are dominant members of the microbial community in the digestive tracts of Scarabaeidae and Passalidae larvae. Further, these organisms seem to partake directly in cellulose degradation and they also intervene in other metabolic reactions. Considering that these MAGs represent potentially undescribed organisms that are both present in high abundance in the gut of these xylophagous beetles and encode for important genes necessary to obtain nutrients out of their recalcitrant food source, they are ideal candidates for further isolation in pure culture to elucidate their definitive role in this system. |
| País: | Kérwá |
| Institución: | Universidad de Costa Rica |
| Repositorio: | Kérwá |
| OAI Identifier: | oai:kerwa.ucr.ac.cr:10669/79951 |
| Acceso en línea: | https://hdl.handle.net/10669/79951 |