Survival strategies ofEnterococcus mundtiiin the gut ofSpodoptera littoralis: a live report

Abstract

21The complex interaction between a higher organism and its resident gut flora is a subject of 22 immense interest in the field of symbiosis. Many insects harbor a complex community of 23 microorganisms in their gut. Larvae of Spodoptera littoralis, a lepidopteran pest which is 24 prevalent in tropical and subtropical regions of the world, have a tube-like gut structure 25 containing a simple bacterial community. This community varies both spatially (along the 26 length of the gut) and temporally (during the life cycle of the insect). 27To monitor the dynamics and rapid adaptation of microbes to the gut conditions, a GFP-tagged 28 reporter E. mundtii was constructed. After feeding to early instar S. littoralis larvae, the tagged-29 microbes recovered from the fore and hind guts by flow cytometry. The fluorescent reporter 30 confirmed the persistence of E. mundtii in the gut. RNA-sequencing of the sorted bacteria 31 highlighted various strategies that the symbiont employs to survive, including upregulated 32 pathways for tolerating alkaline stress, forming biofilms and two-component signaling systems, 33 resisting oxidative stress and quorum sensing. Although these symbionts depend on the host for 34 amino acid and fatty acids, differential regulation among various metabolic pathways points to 35 an enriched lysine synthesis pathway in the hindgut of the larvae. 36 37 animals, pests or pollinators of food crops, and as cyclers of carbon and nitrogen during the 43 decomposition of plant biomass (1) 44 There are several factors that determine the gut bacterial composition in insects. The gut can be 45 compartmentalized, resulting in structures that vary according to the complexity of the microbial 46 communities. Insects with a straight, tube-like gut usually possess a less diverse microbial 47 population compared to species with invaginations and deep pouches (1). Other factors that 48 shape the gut population include the following: oxygen level, gut pH, the presence of digestive 49 enzymes, antimicrobial compounds, and insect diet (2, 3). Although most bacteria have an 50 affinity for neutral pH, several acidophiles and alkalophiles have adapted to extreme pH 51 conditions. 52 Gut microbes can be either vertically or horizontally transmitted. Vertical transmission allows 53 bacterial transfer (from the ovaries to the egg shells) to the next generation (4), whereas 54 horizontal transmission occurs over the course of the life cycle, through diet and social behavior. 55 Regardless of how bacteria are transmitted, microbial populations may be unstable during early 56 developmental stages (5, 6). For example, in holometabolous insects, a complete metamorphosis 57 of the gut occurs in the larva, through pupal and adult stages, resulting in microbial turnover and 58 variable microbial counts (5).59 Insects are helped by their bacterial and fungal symbionts with functions relating to the digestion 60 of complex plant carbohydrates and amino acids, the assimilation of vitamins and the 61 development of defensive str...

High nitrogen in maize enriches gut microbiota conferring insecticide tolerance in lepidopteran pest Spodoptera litura

“…E. mundtii with adherence properties can form a biofilm layer on the gut wall to help insect adapt to altered environments ( Mazumdar et al., 2021b ). Probiotic characterization of E. mundtii was observed from larval gut of Plutella xylostella ( Mazumdar et al., 2021a ). Members of other gut microbiomes can also degrade insecticides in vitro .…”

Host-Adapted Strains of Spodoptera frugiperda Hold and Share a Core Microbial Community Across the Western Hemisphere

“…It is noteworthy that Enterococcus is the most prevalent and abundant group identified in the gut microbiota of Spodoptera species [78, 79, 83], and also the most active in the gut of S. frugiperda [84]. Additionally, it has been demonstrated that Enterococcus mundtii is effective in colonizing and forming biofilm in the gut of Spodoptera littoralis [22, 27]. There is also evidence that E. mundtii can be inherited by S. littoralis through vertical transmission [23].…”

“…Finally, the high variation in the composition of the microbial community driven by host plants would difficult the occurrence of associations that could hold through the required evolutionary time in order to allow the selection and establishment of true gut residents [21]. Nevertheless, other studies have shown that even in hostile environments as the midgut of lepidopteran larvae, there are evidence of gut colonization by certain bacterial groups [22–24]. In addition, gut-resident bacteria of lepidopteran larvae were demonstrated to play important physiological roles for their hosts [25, 26]; besides, the continuous association with their hosts for some of these microbes has been proved as they are horizontally transmitted [27].…”

Gut microbiota of the rice and corn strains of >i<Spodoptera frugiperda>/i<: diversity and function

“…Finally, the high variation in the composition of the microbial community driven by host plants would difficult the occurrence of associations that could hold through the required evolutionary time in order to allow the selection and establishment of true gut residents . Nevertheless, other studies have shown that even in hostile environments as the midgut of lepidopteran larvae, there are evidence of gut colonization by certain bacterial groups Mazumdar et al, 2020;. In addition, gut-resident bacteria of lepidopteran larvae were demonstrated to play important physiological roles for their hosts (Yongqi Shao, Arias-Cordero, Guo, Bartram, & Boland, 2014;Xia, Lan, Tao, Lin, & You, 2020); besides, the continuous association with their hosts for some of these microbes has been proved as they are horizontally transmitted (Y. .…”