Negative Impact of Pseudomonas aeruginosa Y12 on Its Host Musca domestica

Application of bacteria and bacteriophage cocktails for biological control of houseflies

BACKGROUND

Houseflies, Musca domestica L., are an ubiquitous pest that can transmit numerous diseases and threaten human health. Increasing insecticide resistance shown by houseflies necessitates the develop new control alternatives. The housefly gut is densely colonized with microorganisms that interact with each other dynamically and benefit the host's health. However, the impact of multiple symbiotic bacteria on the composition of housefly gut microbiota and the host's activities remains unclear.

METHODS

We isolated and cultured 12 bacterial species from the intestines of housefly larvae. We also isolated seven bacteriophages to precisely target the regulation of certain bacterial species. Using 16S rRNA high-throughput gene sequencing, we analyzed the bacterial diversity after orally administering bacteria/phage cocktails to houseflies.

RESULTS

Our results showed that larval growth was promoted, the abundance of beneficial bacteria, such as Klebsiella and Enterobacter, was increased and the abundance of harmful bacteria, such as Providencia, Morganella and Pseudomonas, was decreased in housefly larvae fed with the beneficial bacteria cocktail. However, oral administration of both beneficial and harmful bacterial phage cocktails inhibited larval growth, probably due to the drastic alteration of gut flora. Untargeted metabolomics using liquid chromatography-mass spectrometry showed that disturbances in gut microbiota changed the larval metabolite profiles. Feeding experiments revealed that disrupting the intestinal flora suppressed the beneficial bacteria and increased the harmful bacteria, causing changes in the metabolites and inhibiting larval growth.

CONCLUSIONS

Based on our results, bacteria/phage cocktails are effective tools for regulating the intestinal flora of insects and have a high potential as a biological control agent for incorporation into an integrated pest management program.

Klebsiella pneumoniae in the intestines of Musca domestica larvae can assist the host in antagonizing the poisoning of the heavy metal copper

BACKGROUND

Musca domestica larvae are common saprophytes in nature, promoting the material-energy cycle in the environment. However, heavy metal pollution in the environment negatively affects their function in material circulation. Our previous research found that some intestinal bacteria play an important role in the development of housefly, but the responses of microbial community to heavy metal stresses in Musca domestica is less studied.

RESULTS

In this study, CuSO4, CuSO4-Klebsiella pneumoniae mixture and CuSO4-K. pneumoniae phage mixture were added to the larval diet to analyze whether K. pneumoniae can protect housefly larvae against Cu2+ injury. Our results showed that larval development was inhibited when were fed with CuSO4, the bacterial abundance of Providencia in the intestine of larvae increased. However, the inhibition effects of CuSO4 was relieved when K. pneumoniae mixed and added in larval diets, the abundance of Providencia decreased. Electron microscope results revealed that K. pneumoniae showed an obvious adsorption effect on copper ion in vitro.

CONCLUSIONS

Based on the results we assume that K. pneumoniae could adsorb Cu2+, reduce Cu2+ impact on gut community structure. Our study explains the role of K. pneumoniae antagonizing Cu2+, which could be applied as a probiotic to saprophytic bioantagonistic metal contamination.

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

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.

Aerobic and facultative anaerobic Klebsiella pneumoniae strains establish mutual competition and jointly promote Musca domestica development

Introduction

The gut microenvironment in housefly harbors a rich and diverse microbial community which plays a crucial role in larval development. However, little is known about the impact of specific symbiotic bacteria on larval development as well as the composition of the indigenous gut microbiota of housefly.

Methods

In the present study, two novel strains were isolated from housefly larval gut, i.e., Klebsiella pneumoniae KX (aerobe) and K. pneumoniae KY (facultative anaerobe). Moreover, the bacteriophages KXP/KYP specific for strains KX and KY were used to analyse the effects of K. pneumoniae on larval development.

Results

Our results showed that dietary supplementation with K. pneumoniae KX and KY individually promoted housefly larval growth. However, no significant synergistic effect was observed when the two bacterial strains were administered in combination. In addition, using high-throughput sequencing, it was demonstrated that the abundance of Klebsiella increased whereas that of Provincia, Serratia and Morganella decreased when housefly larvae received supplementation with K. pneumoniae KX, KY or the KX-KY mixture. Moreover, when used combined, K. pneumoniae KX/KY inhibited the growth of Pseudomonas and Providencia. When the abundance of both bacterial strains simultaneously increased, a balance in total bacterial abundance was reached.

Discussion

Thus, it can be assumed that strains K. pneumoniae KX and KY maintain an equilibrium to facilitate their development in housefly gut, by establishing competition but also cooperation with each other to maintain the constant composition of gut bacteria in housefly larvae. Thus, our findings highlight the essential role of K. pneumoniae in regulating the composition of the gut microbiota in insects.

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

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.

Enterobacter hormaechei in the intestines of housefly larvae promotes host growth by inhibiting harmful intestinal bacteria

BACKGROUND

As a pervasive insect that transmits a variety of pathogens to humans and animals, the housefly has abundant and diverse microbial communities in its intestines. These gut microbes play an important role in the biology of insects and form a symbiotic relationship with the host insect. Alterations in the structure of the gut microbial community would affect larval development. Therefore, it is important to understand the mechanism regulating the influence of specific bacteria on the development of housefly larvae.

METHODS

For this study we selected the intestinal symbiotic bacterium Enterobacter hormaechei, which is beneficial to the growth and development of housefly larvae, and used it as a probiotic supplement in larval feed. 16S rRNA gene sequencing technology was used to explore the effect of E. hormaechei on the intestinal flora of housefly larvae, and plate confrontation experiments were performed to study the interaction between E. hormaechei and intestinal microorganisms.

RESULTS

The composition of the gut microflora of the larvae changed after the larvae were fed E. hormaechei, with the abundance of Pseudochrobactrum, Enterobacter and Vagococcus increasing and that of Klebsiella and Bacillus decreasing. Analysis of the structure and interaction of larval intestinal flora revealed that E. hormaechei inhibited the growth of harmful bacteria, such as Pseudomonas aeruginosa, Providencia stuartii and Providencia vermicola, and promoted the reproduction of beneficial bacteria.

CONCLUSIONS

Our study has explored the influence of specific beneficial bacteria on the intestinal flora of houseflies. The results of this study reveal the important role played by specific beneficial bacteria on the development of housefly larvae and provide insight for the development of sustained biological agents for housefly control through interference of gut microbiota.