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Bacterial Infection and Immune Responses in Lutzomyia longipalpis Sand Fly Larvae Midgut.

Heerman M, Weng JL, Hurwitz I, Durvasula R, Ramalho-Ortigao M - PLoS Negl Trop Dis (2015)

Bottom Line: Depending on the aspects of their development, insects can acquire microbes present in soil, water, and plants.Sand fly larval stages acquire microorganisms from the soil, and the abundance and distribution of these microorganisms may vary depending on the sand fly species or the breeding site.Moreover, bacterial distribution, and likely the ability to colonize the gut, is driven, at least in part, by a gradient of pH present in the gut.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
The midgut microbial community in insect vectors of disease is crucial for an effective immune response against infection with various human and animal pathogens. Depending on the aspects of their development, insects can acquire microbes present in soil, water, and plants. Sand flies are major vectors of leishmaniasis, and shown to harbor a wide variety of Gram-negative and Gram-positive bacteria. Sand fly larval stages acquire microorganisms from the soil, and the abundance and distribution of these microorganisms may vary depending on the sand fly species or the breeding site. Here, we assess the distribution of two bacteria commonly found within the gut of sand flies, Pantoea agglomerans and Bacillus subtilis. We demonstrate that these bacteria are able to differentially infect the larval digestive tract, and regulate the immune response in sand fly larvae. Moreover, bacterial distribution, and likely the ability to colonize the gut, is driven, at least in part, by a gradient of pH present in the gut.

No MeSH data available.


Related in: MedlinePlus

pH of the sand fly larval gut.Third instar sand fly larvae were fed with pH indicators Bromothymol blue (A) and Phenol red (B). Shown is the distribution of each indicator within live sand fly larvae guts, with the predicted pH for each area of the gut indicated. Live 3rd instar sand fly larvae are shown from left (posterior or caudal setae) to right (anterior or head).
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pntd.0003923.g002: pH of the sand fly larval gut.Third instar sand fly larvae were fed with pH indicators Bromothymol blue (A) and Phenol red (B). Shown is the distribution of each indicator within live sand fly larvae guts, with the predicted pH for each area of the gut indicated. Live 3rd instar sand fly larvae are shown from left (posterior or caudal setae) to right (anterior or head).

Mentions: To further investigate what could be driving such a distinct microbial distribution, we assessed the gut pH range within larvae in vivo, and compared it to pH growth assays for the two GFP-expressing bacteria in vitro. LB-agar supplemented with pH indicators Bromothymol blue or Phenol red were fed to larvae, and the color gradient generated was visible through the translucent cuticle of larvae using light microscopy. Intensity of colors varied between larvae due to the initial ingestion time, load size, and bolus movement across the gut. Fifteen larvae of each treatment were compared to the pH references. The Bromothymol blue dye has a range of pH from 6 to 7.6, and Phenol red has a range of 6.8 to 8.4. Previous results on L. longipalpis larval gut pH indicated a basic pH >9 in the anterior portion and an more acidic pH >6.5 in the posterior portion of the midgut [18]. Larvae fed on thymol blue (at concentrations of 0.4% and 0.1%) displayed a green-colored gradient that was not easily distinguishable between pHs 8.5 to 9.5 through the larval cuticle. Two other pH indicators, alizarine yellow and thymolphthalein, were considered during our studies. However, because of our choice of using whole larva, the output colors of these pH indicators were not suitable for visualization through the insect cuticle. The results shown in Fig 2 confirm such a pH gradient in the L. longipalpis larvae, clearly pointing to a basic pH for the anterior part of the midgut, including the proventriculus (PV), and an acidic pH in the posterior part of the midgut.


Bacterial Infection and Immune Responses in Lutzomyia longipalpis Sand Fly Larvae Midgut.

Heerman M, Weng JL, Hurwitz I, Durvasula R, Ramalho-Ortigao M - PLoS Negl Trop Dis (2015)

pH of the sand fly larval gut.Third instar sand fly larvae were fed with pH indicators Bromothymol blue (A) and Phenol red (B). Shown is the distribution of each indicator within live sand fly larvae guts, with the predicted pH for each area of the gut indicated. Live 3rd instar sand fly larvae are shown from left (posterior or caudal setae) to right (anterior or head).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495979&req=5

pntd.0003923.g002: pH of the sand fly larval gut.Third instar sand fly larvae were fed with pH indicators Bromothymol blue (A) and Phenol red (B). Shown is the distribution of each indicator within live sand fly larvae guts, with the predicted pH for each area of the gut indicated. Live 3rd instar sand fly larvae are shown from left (posterior or caudal setae) to right (anterior or head).
Mentions: To further investigate what could be driving such a distinct microbial distribution, we assessed the gut pH range within larvae in vivo, and compared it to pH growth assays for the two GFP-expressing bacteria in vitro. LB-agar supplemented with pH indicators Bromothymol blue or Phenol red were fed to larvae, and the color gradient generated was visible through the translucent cuticle of larvae using light microscopy. Intensity of colors varied between larvae due to the initial ingestion time, load size, and bolus movement across the gut. Fifteen larvae of each treatment were compared to the pH references. The Bromothymol blue dye has a range of pH from 6 to 7.6, and Phenol red has a range of 6.8 to 8.4. Previous results on L. longipalpis larval gut pH indicated a basic pH >9 in the anterior portion and an more acidic pH >6.5 in the posterior portion of the midgut [18]. Larvae fed on thymol blue (at concentrations of 0.4% and 0.1%) displayed a green-colored gradient that was not easily distinguishable between pHs 8.5 to 9.5 through the larval cuticle. Two other pH indicators, alizarine yellow and thymolphthalein, were considered during our studies. However, because of our choice of using whole larva, the output colors of these pH indicators were not suitable for visualization through the insect cuticle. The results shown in Fig 2 confirm such a pH gradient in the L. longipalpis larvae, clearly pointing to a basic pH for the anterior part of the midgut, including the proventriculus (PV), and an acidic pH in the posterior part of the midgut.

Bottom Line: Depending on the aspects of their development, insects can acquire microbes present in soil, water, and plants.Sand fly larval stages acquire microorganisms from the soil, and the abundance and distribution of these microorganisms may vary depending on the sand fly species or the breeding site.Moreover, bacterial distribution, and likely the ability to colonize the gut, is driven, at least in part, by a gradient of pH present in the gut.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
The midgut microbial community in insect vectors of disease is crucial for an effective immune response against infection with various human and animal pathogens. Depending on the aspects of their development, insects can acquire microbes present in soil, water, and plants. Sand flies are major vectors of leishmaniasis, and shown to harbor a wide variety of Gram-negative and Gram-positive bacteria. Sand fly larval stages acquire microorganisms from the soil, and the abundance and distribution of these microorganisms may vary depending on the sand fly species or the breeding site. Here, we assess the distribution of two bacteria commonly found within the gut of sand flies, Pantoea agglomerans and Bacillus subtilis. We demonstrate that these bacteria are able to differentially infect the larval digestive tract, and regulate the immune response in sand fly larvae. Moreover, bacterial distribution, and likely the ability to colonize the gut, is driven, at least in part, by a gradient of pH present in the gut.

No MeSH data available.


Related in: MedlinePlus