A comprehensive account of functional role of insect gut microbiome in insect orders

Symbiotic association of microbes with insects have given insects, physiological and ecological benefits. Insects from all taxonomical orders have gut microbiota, which helps the insect host by providing nutrients, promoting digestion, regulating growth and metabolism by conditioning and altering signalling pathways to achieve homeostasis and immunity. In recent years, with advances in metagenomics and bioinformatics several gut microbes residing in insects have been identified. Among these Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes are the dominant phyla found in the guts of different insect orders. Insect gut microbiota experience a period of stress in the host's gut environment and are a good source of active biologics, which can be bioprospected for commercial application. In insect hosts, gut microbiota influences feeding behaviour, provides survival benefits by metabolising plant secondary metabolites, chemical pesticides and also degrade plastics. This review is an attempt to comprehensively compile the research on gut microbiome done in various insect orders and addresses the fundamental importance of gut bacteria, in field of insect nutrition control, survival benefits like immunity, pesticide and plastic degradation, and developing commercially important products. In this review, we discuss the most competent community of microbes in different niches of different orders of insects and their symbiotic relationship.