DETECTION OF PENICILLIN-BINDING PROTEINS IN THE ENDOSYMBIONT OF THE TRYPANOSOMATID CRITHIDIA-DEANEI

Growth by serial transfers of the trypanasomatid Crithidia deanei in c ulture medium containing 1 mg/ml of the beta-lactam antibiotics ampici llin or cephalexin resulted in shape distortion of its endosymbiont. T he endosymbiont first appeared as filamentous structures with restrict ed areas of membrane damage. An increase of electron lucid areas was a lso observed in the endosymbiont matrix. The continuous treatment with beta-lactam antibiotics, resulted in endosymbiont membranes fragmenta tion; and later on the space previously occupied by the symbiont was i dentified as an electron lucid area in the host cytoplasm. The putativ e targets of beta-lactam antibiotic were two membrane-bound penicillin -binding proteins (PBPs) detected in the Sarkosyl-soluble fraction of purified symbionts labeled with [H-3]-benzylpenicillin. The apparent m olecular weight of the proteins were 90 kDa (PBP1) and 45 kDa (PBP2). PBP2 represented 85% of the total PBP content in the membrane fraction of the endosymbionts. Competition experiments using the tested antibi otics and [3H]-benzylpenicillin showed that ampicillin and cephalexin have half saturating concentrations considerably higher than [H-3]-ben zylpenicillin and indicated that PBP1 is the probable lethal target of the antibiotics tested. These results suggest that a physiologically active PBP is present in the cell envelope of C. deanei endosymbionts and may play important roles in the control of processes such as cell division and shape determination.