Bacteria associated with the digestive system of the slug Deroceras reticulatum are not required for protein digestion

Bacteria were isolated from the crop, digestive glands and salivary glands of the field slug Deroceras reticulatum (Muller). The digestive gland was t he most densely populated organ with about x3 and x400 more bacterial colon y forming units (CFU) mg(-1) of tissue than in the crop and salivary glands , respectively. Growth on plate-count agar incorporating gelatin showed tha t 34, 16 and 3% of the total numbers of CFU present in the salivary gland, digestive gland and crop, respectively, secreted extracellular proteinases that degraded gelatin. Administration of antibiotics (chloramphenicol or te tracycline plus chlortetracycline) to slugs in an artificial diet reduced t he numbers of total and proteolytic CFU present by 98-99%. Although protein ase-secreting bacteria were present in all organs studied, only the crop po ssessed significantly greater proteolytic activity (x3 at pH 8.0) when slug s were not fed on diet containing antibiotics. (C) 1999 Elsevier Science Lt d. All rights reserved.