The presence of a symbiotic bacterium in Strigomonas culicis is related to differential ecto-phosphatase activity and influences the mosquito–protozoa interaction

• Strigomonas culicis is a monoxenic protozoan which hosts an obligatory symbiotic bacterium.
• The presence of the symbiont is essential to the establishment of the protozoan in the insect midgut.
• Strigomonas culicis ecto-phosphatase activity is influenced by the symbiont.
• Strigomonas culicis ecto-phosphatase activity is involved in attachment to Aedes aegypti midgut and salivary glands.

Strigomonas culicis is a monoxenous trypanosomatid that co-evolves with a symbiotic bacterium in a mutualistic relationship that is characterized by intense metabolic exchanges between both partners. S. culicis infects and colonizes the Aedes aegypti mosquito midgut, reaches its hemocoel and then invades the salivary glands. An artificial aposymbiotic strain is unable to colonize insects, reinforcing the idea that the bacterium influences the protozoan surface composition and cell interaction. Here, we report the characterization of the hydrolytic activity of ecto-phosphatases evaluated in symbiont-bearing and aposymbiotic strains of S. culicis by incubating the protozoa with p-nitrophenyl phosphate (pNPP) at different pH levels, in the presence of phosphatase inhibitors, and with several divalent metals. The symbiont-bearing and aposymbiotic cells differ in their ecto-phosphatase enzymes, based on their activities and specificities. Furthermore, the ability of the protozoan to bind to the mosquito midgut and salivary glands was impaired by ecto-phosphatase inhibition. Taken together, our data suggest that the symbiont influences the host protozoan ecto-phosphatase activity and indicate a possible role of this enzyme during mosquito tissue colonization by S. culicis.

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