Serratia marcescens in the intestine of housefly larvae inhibits host growth by interfering with gut microbiota

Abstract

Background The structure of gut microbiota is highly complex. Insects have ubiquitous associations with intestinal symbiotic bacteria, which play essential roles. Thus, understanding how changes in the abundance of a single bacterium interfere with bacterial interactions in the insect’s gut is important. Methods Here, we analyzed the effects of Serratia marcescens on the growth and development of housefly larvae using phage technology. We used 16S rRNA gene sequencing technology to explore dynamic diversity and variation in gut bacterial communities and performed plate confrontation assays to study the interaction between S. marcescens and intestinal microorganisms. Furthermore, we performed phenoloxidase activity assay, crawling assay, and trypan blue staining to explore the negative effects of S. marcescens on housefly larvae’s humoral immunity, motility, and intestinal organization. Results The growth and development of housefly larvae were inhibited after feeding on S. marcescens, and their intestinal bacterial composition changed with increasing abundance of Providencia and decreasing abundance of Enterobacter and Klebsiella. Meanwhile, the depletion of S. marcescens by phages promoted the reproduction of beneficial bacteria. Conclusions In our study, using phage as a tool to regulate the abundance of S. marcescens, we highlighted the mechanism by which S. marcescens inhibits the growth and development of housefly larvae and illustrated the importance of intestinal flora for larval development. Furthermore, by studying the dynamic diversity and variation in gut bacterial communities, we improved our understanding of the possible relationship between the gut microbiome and housefly larvae when houseflies are invaded by exogenous pathogenic bacteria. Graphical Abstract

Application of bacteria and bacteriophage cocktails for biological control of houseflies

“…The abundance of harmful bacteria, such as P. aeruginosa, increased in the HBP group. Our previous results revealed that specific bacteria can be knocked down by its targeting phage [ 29 , 35 ], enabling gut microbial regulation. However, the abundance of harmful bacteria was not significantly reduced in the HBP group.…”

“…The impact of an entomopathogenic fungi treatment may be more persistent and thereby result in longer-term control; however, bacteria are faster acting than fungi once they gain entry to the host. S. marcescens as a common natural bioinsecticide is pathogenic to insects [ 29 , 56 ]. Bacillus thuringiensis has different proteins that are toxic to a variety of insects [ 57 ], which will provide various alternatives for insect control and for overcoming the pesticides resistance [ 58 ].…”

“…The crawling ability of housefly larvae was assessed in an assay involving trypan blue staining using the protocol described previously [ 29 ].…”

“…Lysinibacillus sphaericus has been used effectively for the biological control of various mosquito species by producing a toxin [ 27 ]. In our previous research, S. marcescens and Pseudomonas aeruginosa were found to affect larval development in houseflies by inhibiting the growth of beneficial bacteria and reducing larval humoral immunity [ 28 , 29 ]. Given that various mixed bacterial biological agents have received little attention for housefly control, the goal of this study was to examine the effects of bacteria and bacteriophage cocktails on the housefly as alternative biological control agents.…”

Comprehensive Comparison of Effects of Antioxidant (Astaxanthin) Supplementation from Different Sources in Haliotis discus hannai Diet

“…There has been limited research to understand the function and effect of Serratia in animals’ gut. Present acknowledgements about Serratia have been divergent: some studies have held the view that Serratia is a Gram-negative opportunistic pathogen, and can injure intestinal epithelial cells causing gastrointestinal problems, and has consequences for the host’s physiology and health [ 52 , 53 , 54 ]. On the contrary, Bai et al [ 55 ] illustrated that Serratia can activate innate immune responses of Drosophila through Toll and Imd immune-signaling pathways to achieve the goal of anti- Plasmodium and antibacterial immune defense.…”