| The red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera:Curculionidae), native to south Asia and Melanesia, is an invasive species for China since 1990 as a serious pest of various palm species. In many insects, the gut microbiota is critical for the host health through their impacts on nutrition, defenses, or other physiological functions. Few studies have been conducted on RPW gut microbiota in the larval or adult stages, however, the bacterial community composition across different life stages is far from being well understood. This study aimed to explore the complexity and variability of the gut microbiota of Rhynchophorus ferrugineus across the various groups and life stages by combining the traditional culture-dependent and culture-independent techniques, the modern Illumina Highthroughput sequencing. Moreover, the effects of gut microbiota on host nutrient allocation were determined as well.The culture-dependent method in combination of molecular and biochemical characterization identified 14 different isolates (RPWL1-RPWL14) from 10 genera in two phyla, Proteobacteria (90%) and Firmicutes (10%) from the gut of RPW larvae. The gut microbiota was variable and ranges from facultative anaerobes to opportunistic pathogens, dominated by Enterobacter cloacae (23%), Klebsiella sp. (21%), Citrobacter sp. (15%), Cronobacter sp. (12%), Serratia marcescens (7%), Salmonella enterica (6%), Raoultella sp. (4%), and Shigella sp. (3%) in Enterobacteriaceae, while Lactococcus lactis (4%), Staphylococcus sp. (4%), and Bacillus cereus (1%) in Streptococcaceae, Staphylococcaceae, and Bacillaceae, respectively.By the 16S rRNA gene-based Highthroughput sequencing of V4 region, we observed that RPW guts were dominated by Proteobacteria and Firmicutes that comprised of more than 90% of the entire RPW microbiota across the different stages and were assigned to the family Enterobacteriaceae (almost 60%), Lactobacillaceae, Entomoplasmataceae, Commonadaceae, Enterococcaceae, Streptococcaceae, Rhodobacteraceae and others in significantly different proportions. The female had a significantly higher relative abundance of Enterobacteriaceae (87%) compared to the male (41.23%). Comparing the bacterial diversity and composition of different field-caught and lab-reared larvae groups of RPW, we found that Proteobacteria inhabited in the guts of HL (Hainan larvae) and LL larvae (Longyan larvae) accounted for about 80%, and more than 60% in LABL (Lab-reared larvae) and PL (Fuqing larvae) of the RPW larvae.Administration of antibiotics significantly altered the community composition and relative abundances of RPW gut microbiota. Comparing the two groups, the community diversity was significantly higher in CK RPW and the relative abundances of the bacterial composition in the two groups vary significantly. However, the abundant phyla (Proteobacteria, Firmicutes, and Bacteroidetes) remained the same with markedly different proportion. Interestingly, we also observed a negative association between the Alphaproteobacterium, Acetobacteraceae and the host TG content and, between the Lactobacillales and the host glucose content. The glucose and protein contents were significantly higher in the conventionally reared (CK RPW) RPW larvae while the triglyceride (TG) content was significantly elevated in the dysbiotic larvae group (AT RPW). However, the body weight between the two groups was not significantly different between the two groups. The results of this study showed that the RPW gut microbiota is the important factor that affects the energy allocation and host nutrition.The results of this study would expand our knowledge about the robust insect- symbionts association and can pave the path for studying the insect-microbe interactions which can ultimately be incorporated in the designing of a novel microbe-based bio-control strategy. |
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