ANAEROBIC NITRATE RESPIRATION BY ERWINIA-CAROTOVORA SUBSP ATROSEPTICADURING POTATO-TUBER INVASION

The in planta induction of anaerobic nitrate respiration by Erwinia ca rotovora subsp. atroseptica in relation to the in situ oxygen status i n soft rotting potato tubers has been investigated. In vitro experimen ts have shown that nitrate was required for the induction of respirato ry nitrate reductase activity in E. carotovora. In addition, oxygen wa s found to repress this activity. Expression of respiratory nitrate re ductase was found in E. carotovora cells extracted from soft rotting p otato tuber tissue. However, the rate of nitrite production in these c ells was approximately 70-fold lower than the rate recorded in fully i nduced anaerobic cultures. Oxygen measurements in soft rotting potato tubers indicated that the invading bacteria encounter the lowest oxyge n concentration at the interphase between healthy and macerated tissue . Consequently, growth of bacteria present in this specific zone will be stimulated by nitrate which is present in sufficient amounts in tub er tissue. A high nitrate content of the tuber will most likely facili tate the proliferation of E. carotovora in the tuber tissue.