THE LIFE OF ROOT-NODULE BACTERIA IN THE ACIDIC UNDERGROUND

The effects of low pH on the growth and survival of root nodule bacter ia are important in determining the success of legume inoculation in p ractical agriculture. The mechanisms for maintenance of intracellular pH (pH(i)) are crucial, but little is yet known about them in root nod ule bacteria. Like other Gram-negative bacteria, root nodule bacteria show an adaptive acid tolerance response, with growth at moderately ac idic conditions protecting against an extreme acid shock. Variations i n acid tolerance within species of root nodule bacteria imply a geneti c basis to low pH tolerance and studies of acid-sensitive mutants sugg est that as many as 20 genes could be involved. A general model for ac id tolerance in root nodule bacteria is presented.