Abstract
Intestinal homeostasis mechanisms of the haematophagous triatomines regulate the development of mutualistic symbionts and other gut bacteria. Investigating antimicrobial compounds of these insects, we have determined spectrophotometrically that the bacteriolytic activity is between pH 3 and pH 9 using homogenates of fifth instar Triatoma infestans stomachs and small intestines from unfed bugs and up to 50 days after feeding. The activity against Gram-positive Micrococcus luteus was strongest at pH 4 and pH 7 and was higher in the stomach than in the small intestine. Symbiotic Rhodococcus triatomae were not lysed. Lysis of Gram-negative Escherichia coli showed a maximum at pH 7 in the stomach and at pH 5 in the small intestine. Bacteriolytic activity against both M. luteus and E. coli was reduced 24 h after feeding, then increased, and at 50 days after feeding was strongly reduced. In zymographs, the activity against M. luteus was mainly correlated to proteins of about 16 kDa. At different periods of time after feeding, seven bands of lysis appeared between 15 and 40 kDa and more bands using extracts of the small intestine than those of the stomach. This is the first proof for the synthesis of antibacterial proteins of 22–40 kDa in triatomines.
Highlights
Triatomines, vectors of Trypanosoma cruzi (Chagas, 1909), ingest large amounts of blood, with nymphs taking 6–12 times their own body weight [1]
The relatively similar concentrations of protein in the stomach of T. infestans between 5 and 40 daf more accurately reflects the specific digestive behaviour of triatomines than the data for R. prolixus, since in triatomines no digestion of haemoglobin occurs in the stomach and the concentrated blood is passed in small portions to the small intestine
In the first detailed investigation of the bacteriolytic activity in the gut of triatomines, the Grampositive bacterium, M. luteus, was used as the substrate with a sodium acetate buffer ranging from pH 5.0 to 7.5 [16]
Summary
Triatomines, vectors of Trypanosoma cruzi (Chagas, 1909) (the etiologic agent of Chagas disease in the New World), ingest large amounts of blood, with nymphs taking 6–12 times their own body weight [1]. The blood passes the oesophagus and the beginning of the midgut, the cardia, and is stored in the strongly distensible stomach. There, the blood remains mainly undigested, but is concentrated and the erythrocytes are lysed. Small portions of the concentrated blood are passed from the stomach to the digestive part of the midgut, the small intestine (summarized by [1,2]). Digestion takes place slowly over a long time, lasting 14 days in fully engorged females of Triatoma infestans [3], and more than 35 days in fully engorged fifth instar nymphs of this species [4]. The nutrients are needed for the development to the instar
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