Gut Microbiota Dynamics in Natural Populations of Pintomyia evansi under Experimental Infection with Leishmania infantum

Identification of Ochrobactrum as a bacteria with transstadial transmission and potential for application in paratransgenic control of leishmaniasis

Leishmaniasis is a zoonotic vector-borne disease with worldwide distribution. All current approaches in leishmaniasis control or development of vaccines/cures showed only limited success. Recently, paratransgenesis has been marked as a promising strategy for leishmaniasis control. Thus, the investigations of the gut microbial content of sand flies have gained popularity. Gut microbial composition of the laboratory colony of Phlebotomus papatasi was investigated via microbial culturomics approach which refers to the combination of multiple culture conditions and different selective and/or enriched culture mediums, followed by 16S rDNA sequencing. Investigations were conducted on three offspring generations, with six samplings of immature stages (four larval samplings, one pre-pupa, one pupa) and samplings of adults before and after blood feeding. The aim was to determine if microbiome changes during the sand fly development and to identify bacteria with transstadial potential. The presence of 8 bacterial taxa (Bacillus sp., Terribacillus sp., Staphylococcus sp., Alcaligenes sp., Microbacterium sp., Leucobacter sp., Ochrobactrum sp. and Enterobacter sp.), 2 fungi (Fusarium sp. and Acremonium sp.) and 1 yeast (Candida sp.) were recorded. Gram-positive bacteria were more diverse, but gram-negative bacteria were more abundant. All taxa were recorded among immature stage samples, while only one bacterium was detected in adults. Microbial diversity among larval samples was stable, with a steady decrease in pre-pupa and pupa, resulting in the survival of only Ochrobactrum sp. in adults. Abundance of microbes was higher when larvae were actively feeding, with a gradual decrease after larvae stopped feeding and commenced pupation. Ochrobactrum sp. is the bacteria with transstadial potential, worthy of future in-depth analysis for the application in paratransgenic approach for the control of Leishmania sp.

Effects of host species on microbiota composition in Phlebotomus and Lutzomyia sand flies

BACKGROUND

Blood-sucking phlebotomine sand flies are vectors of the protozoan parasites Leishmania spp. Although the intestinal microbiota is involved in a wide range of biological and physiological processes and has the potential to alter vector competence, little is known about the factors that modify the gut microbiota composition of sand flies. As a key step toward addressing this issue, we investigated the impact of host species on the gut bacterial composition in Phlebotomus and Lutzomyia sand flies reared under the same conditions.

METHODS

Bacterial 16S rRNA gene amplification and Illumina MiSeq sequencing were used to characterize the overall bacterial composition of three laboratory-reared sandflies: Phlebotomus papatasi, Ph. duboscqi, and Lutzomyia longipalpis.

RESULTS

Our results showed that the larvae of the three sand fly species harbored almost the same microbes but had different relative abundances. Adult Ph. papatasi and Ph. duboscqi revealed similar microbiome compositions, which were distinct from that of adult Lu. longipalpis. Furthermore, we showed that Ph. papatasi and Ph. duboscqi are hosts for different bacterial genera. The experiment was repeated twice to improve accuracy and increase reliability of the data, and the same results were obtained even when a distinct composition of the microbiome among the same species was identified probably because of the use of different larvae food batch.

CONCLUSIONS

The present study provides key insights into the role of host species in the gut microbial content of different sand fly species reared under the same conditions, which may influence their susceptibility to Leishmania infection.

Detection of Quorum Sensing Signal Molecules, Particularly N-Acyl Homoserine Lactones, 2-Alky-4-Quinolones, and Diketopiperazines, in Gram-Negative Bacteria Isolated From Insect Vector of Leishmaniasis

Gram-negative bacteria are known to use a quorum sensing system to facilitate and stimulate cell to cell communication, mediated via regulation of specific genes. This system is further involved in the modulation of cell density and metabolic and physiological processes that putatively either affect the survival of insect vectors or the establishment of pathogens transmitted by them. The process of quorum sensing generally involves N-acyl homoserine lactones and 2-alkyl-4-quinolones signaling molecules. The present study aimed to detect and identify quorum sensing signaling molecules of AHLs and AHQs type that are secreted by intestinal bacteria, and link their production to their extracellular milieu and intracellular content. Isolates for assessment were obtained from the intestinal tract of Pintomyia evansi (Leishmania insect vector). AHLs and AHQs molecules were detected using chromatography (TLC) assays, with the aid of specific and sensitive biosensors. For identity confirmation, ultra-high-performance liquid chromatography coupled with mass spectrometry was used. TLC assays detected quorum sensing molecules (QSM) in the supernatant of the bacterial isolates and intracellular content. Interestingly, Pseudomonas otitidis, Enterobacter aerogenes, Enterobacter cloacae, and Pantoea ananatis isolates showed a migration pattern similar to the synthetic molecule 3-oxo-C6-HSL (OHHL), which was used as a control. Enterobacter cancerogenus secreted C6-HSL, a related molecules to N-hexanoyl homoserine lactone (HHL), while Acinetobacter gyllenbergii exhibited a migration pattern similar to 2-heptyl-4-quinolone (HHQ) molecules. In comparison to this, 3-oxo-C12-HSL (OdDHL) type molecules were produced by Lysobacter soli, Pseudomonas putida, A. gyllenbergii, Acinetobacter calcoaceticus, and Pseudomonas aeruginosa, while Enterobacter cloacae produced molecules similar to 2-heptyl-3-hydroxy-4-quinolone (PQS). For Pseudomonas putida, Enterobacter aerogenes, P. ananatis, and Pseudomonas otitidis extracts, peak chromatograms with distinct retention times and areas, consistent with the molecules described in case of TLC, were obtained using HPLC. Importantly, P. ananatis produced a greater variety of high QSM concentration, and thus served as a reference for confirmation and identification by UHPLC-MRM-MS/MS. The molecules that were identified included N-hexanoyl-L-homoserine lactone [HHL, C10H18NO3, (M + H)], N-(3-oxohexanoyl)-L-homoserine lactone [OHHL, C10H16NO4, (M + H)], N-(3-oxododecanoyl)-L-homoserine lactone [OdDHL, C16H28NO4, (M + H)], and 2-heptyl-3-hydroxy-4(1H)-quinolone [PQS, C16H22NO2, (M + H)]. Besides this, the detection of diketopiperazines, namely L-Pro-L-Tyr and ΔAla-L-Val cyclopeptides was reported for P. ananatis. These molecules might be potentially associated with the regulation of QSM system, and might represent another small molecule-mediated bacterial sensing system. This study presents the first report regarding the detection and identification of QSM and diketopiperazines in the gut sand fly bacteria. The possible effect of QSM on the establishment of Leishmania must be explored to determine its role in the modulation of intestinal microbiome and the life cycle of Pi. evansi.