Metagenomic Approaches for Insect Symbionts

Abstract

Insects, the most successful groups in animal kingdom, harbor diverse groups of microbes, such as bacteria, archaea, fungi, protozoa, and viruses, which profoundly influence their survival and adaptations over a wide range of ecological niches. These microbes are associated with their host insects permanently or transiently and such associations may be beneficial or harmful to the host insect under various instances. Attempts were made earlier to characterize insect microbiome by isolation and cultivation techniques and polymerase chain reaction (PCR)-based cloning methods that resulted in identification of a few groups of microbes. The metagenomic approaches under the next-generation sequencing platforms provide unparallel opportunities to understand the composition of the microbiome and their functional role in the biology of the insects, thus expanding our understanding from a single microbial species to the whole community. These approaches provide an ample opportunity to understand the components of the microbiome that can potentially and collectively affect the behavior and physiological traits of insects through genetic and metabolic interactions. For instance, endosymbionts (i.e., microbes that live inside host cells or tissues) depend on the insect hosts for obtaining nutrients, provide fitness advantages to their insect hosts in terms of the breakdown of plant cell wall components, viz, cellulose, lignocelluloses, and xylan, supplying essential amino acids and vitamins to host insects, thereby upgrading the nutrient status of their diet, detoxification of lethal insecticide molecules, plant defensive compounds such as phenolics, and production of anti-microbial peptides against insect pathogens. However, in some instances, the microbes may also be pathogenic to the insect hosts by producing insecticidal toxins, which reduce viability and cause morbidity.

The culture-independent metagenomic approach allows us to characterize a variety of genes that microbes possess or are expressing, which signifies ‘what they are doing’ within the host. It also enables us to compare the performance of insect with changes in their microbiome composition. These approaches have a wide range of applications apart from the study of insect’s microbial ecology. The microbiota associated with wood-feeding beetles can be exploited as source of novel enzymes in industrial bioprocesses. The information on microbial genes and enzymes involved in cellulose hydrolysis, vitamin production, and nitrogen fixation can be useful in improving the reliability and efficiency of industrial processes. Furthermore, insect–microbe relationships could be manipulated to improve pest control, by decreasing pest’s fitness or by increasing the efficacy of pest management programs.