Histochemical and Bacteriological Studies on Digestion in Nine Species of Leeches (Annelida: Hirudinea)

Abstract

Previous studies on digestion in the leeches (summarized by Herter, 1936;Harant and Grasse, 1959; Mann, 1962) have been restricted to a few genera, notably Hirudo and Haemopis. Such accounts as are available, however, indicate that the full complement of digestive enzymes normally present in the alimentary system is, in the leeches, much reduced. In Hirudo, for example, the careful experiments of Graetz and Autrum (1935) failed to demonstrate proteases in gut wall extract, and this supported earlier observations by Diwany (1925) that starved Hirudo could not digest milk, egg proteins or peptones injected aseptically into the gut. With Haemopis Autrum and Graetz (1934) and Graetz and Autrum (1935) showed that enzymes for initiating proteolysis (the endopeptidases of modern terminology) are absent, but that a number of those concerned in subsequent stages (exopeptidases) are to be found in extracts of the gut wall.The alimentary system in leeches shows well developed regional differentiation in that a pharynx, oesophagus, crop, intestine and rectum are generally present, but, in contrast, there is little or no differentiation at the cellular level into glandular and absorptive components. This apparent lack of gland cells, apart from salivary glands, lends support to the biochemical evidence that digestive enzymes are reduced in number, although such absence of intercellular differentiation does not ipso facto eliminate the possibility of secretory activity in the gastrodermis.The failure to demonstrate a full range of proteolytic enzymes led Graetz and Autrum (1935) to suggest that bacteria may be concerned in digestive processes, and this possibility was subsequently examined by Busing (1951) and Busing, Doll and Freytag (1953). A single species of bacterium, named by Busing "Pscndomonas hirudinis'' was found consistently in the gut lumen of Hirudo and in vitro studies showed that the microorganism is capable of slowly digesting the blood which is the normal food of this leech. Inclusion of antibiotics in the food

Activity of selected hydrolytic enzymes from leeches (Clitellata: Hirudinida) with different feeding strategies

“…In majority of leeches, food accumulates and is stored in the crop, while most of the food digestion and absorption take place in the undifferentiated intestine (Jennings & van der Lande 1967;van der Lande 1968; Explanations: E -Erpobdella octooculata,…”

“…Only in G. complanata, P. geometra and Helobdella stagnalis (L., 1758), digestion and absorption start in the crop (Jennings & van der Lande 1967). Erythrocytes in the food are completely digested in the crop of P. geometra within 10 days.…”

“…The enzyme system in leeches is not very welldeveloped and the digesting processes are aided by enzymes produced by symbiotic bacteria (Aeromonas, Pseudomonas, Xanthomonas, Klebsiella, Proteobacteria), which also produce antibiotics inhibiting the growth of other bacteria, and vitamins, mainly of the B group (Jennings & van der Lande 1967;Graf 1998;Kikuchi & Fukatsu 2002). The alimentary tract of Hirudo medicinalis (L., 1758) is inhabited only by Aeromonas veronii, which has been found in 20% of patients treated with the medicinal leech (Graf 1998).…”

“…The epithelium which lines the alimentary tract of leeches (gastrodermis) is not morphologically differentiated into secretive and absorptive parts, and histochemical examinations revealed the absence of digestive enzymes, such as endopeptidases, lipases or glucolytic enzymes (Jennings & van der Lande 1967;Sawyer 1986). On the other hand, exopeptidases as well as basic and acidic phosphatases were found to be highly active (Jennings & van der Lande 1967;Fischer 1970;van der Lande 1972).…”

“…On the other hand, exopeptidases as well as basic and acidic phosphatases were found to be highly active (Jennings & van der Lande 1967;Fischer 1970;van der Lande 1972). According to the cited authors, majority of food digestion and absorption processes in leeches occur in their intestine, with exopeptidases (arylamidases) being the only enzymes produced which are capable to digest proteins.…”