Beneficial Bacteria in the Intestines of Housefly Larvae Promote Larval Development and Humoral Phenoloxidase Activity, While Harmful Bacteria do the Opposite

Abstract

The gut microenvironment of houseflies provides unique conditions for microbial colonization. Some gut microorganisms provide benefits for the development of the host by regulating the interaction between the host and intestinal pathogens. Gut microbial alterations can stimulate the host’s immune mechanism to resist pathogen invasion and affect the development of insects. In this study, we isolated 10 bacterial strains from housefly larval intestines. The isolated bacteria were added to the larval diet to analyze the effects of microecological regulation of gut bacteria on larval development. Dynamic changes in gut flora composition after oral administration of specific bacteria were analyzed although 16S rRNA gene high-throughput sequencing technology. To explore the interaction between gut bacteria and the host, the immune response of larvae against the invasion of foreign microorganisms was observed through a phenoloxidase activity experiment. Our results showed that the oral administration of various isolated bacteria had different effects on larval development. Oral administration of beneficial bacteria, including Enterobacter hormaechei, Klebsiella pneumoniae, Acinetobacter bereziniae, Enterobacter cloacae, Lysinibacillus fusiformis and Bacillus safensis, promoted larval development by increasing gut community diversity and the humoral immunity of larvae, while harmful bacteria, including Pseudomonas aeruginosa, Providencia stuartii and Providencia vermicola, influenced larval development by inhibiting the growth of beneficial bacteria and reducing the humoral immunity of larvae. The beneficial bacteria isolated in our research could be applied as good probiotic additives for the intensive feeding of larvae, while isolation of the harmful bacteria provides a basis for the development of pest inhibitors. Furthermore, our research revealed the immune response of housefly phenoloxidase to exogenous microorganism stimulation, providing richer and more comprehensive knowledge of the larval innate immune response.

Shotgun metagenomics reveals the gut microbial diversity and functions in Vespa mandarinia (Hymenoptera: Vespidae) at multiple life stages

“…Other diverse functions of intestinal microbials from adult wasp are also worth attention, especially the metabolic capacity of different substances, including drug metabolism, chloroalkane and chloroalkene degradation, and naphthalene degradation. The degradability of chloroalkene and naphthalene, which are also found in some insects, would enhance insect defense capacity (Zhang Q. et al, 2022 ). In Supplementary Sheet S6 , we observed an increasing trend in the degradation abundance of chloroalkane, chloroalkene, and naphthalene with the lifecycle.…”

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

“…Among them, Providencia , as bacteria associated with a high mortality rate in flies, always remained at a high level [ 46 ]. Research has shown that P. stuartii and P. vermicola , which are “harmful bacteria” in housefly larvae, can significantly inhibit the growth and development of these larvae [ 5 ], proving that Providencia plays a substantial role in the death of houseflies. In contrast, we found that the abundance of Enterobacteria and Klebsiella in the gut of housefly larvae was significantly reduced.…”

“…It has also been reported that Klebsiella oxytoca can be used as a probiotic to improve the mating success rate and viability of B. dorsalis flies [ 48 ]. Meanwhile, the oral intake of the beneficial bacterium E. hormaechei by housefly larvae was shown to increase their growth and development and improve their humoral immunity [ 5 , 9 ]. Additionally, under aseptic conditions, E. cloacae inoculation was found to provide additional protection against infection, which improved fitness [ 49 ].…”

“…The supernatant was extracted after centrifugation at 4 °C and 12000 r/min for 20 min. The enzymatic reaction system was prepared using the same method as described previously [ 5 , 34 ]. After reacting in a 25 °C water bath for 15 min, the OD 405 value was measured.…”

“…The composition of the housefly microbiota depends on the insect’s intestinal environment [ 4 ], and bacteria in the microbiota influence the daily activities of housefly larvae via physiological functions, including nutrition, metabolism, development, behavior, and immunity [ 2 , 3 ]. Gut microbiota alterations can have beneficial effects by stimulating hosts and immune mechanisms, thereby conferring resistance to pathogenic invasion [ 5 ]. Conversely, an imbalanced or depleted microbiome may be harmful to insects, leading to various diseases [ 6 ].…”