Antibiotics and Bacterial Auxotrophic Mutants in the Co-cultivation of Plant Protoplasts and Bacterial Cells or Spheroplasts

We have studied the toxicity of six β-lactam antibiotics to Nicotiana tabacum cv. xanthi cells and protoplasts as well as their effect on Agrobacterium tumefaciens cells containing the bla gene from pBR322 and the plasmid pPHlJl of the P incompatibility group. Relatively high doses of ampicillin, cloxacillin, cefoxitin and vancomycin can be tolerated by plant cells while allowing rapid elimination of A. tumefaciens cells. However, young cells originating from protoplasts are more sensitive to antibiotics. A combination of cefoxitin and cloxacillin allows good control of bacterial proliferation and has no adverse effect on plant protoplast division. Histidine- and leucine-requiring mutants of A. tumefaciens proliferate very slowly in the presence of dividing protoplasts whereas E. coli HB101 carrying a bla gene do not. A. rhizogenes was also found to be sensitive to cefoxitin.