INTERACTIONS BETWEEN POPULATIONS OF PSEUDOMONAS-PUTIDA LEADING TO THE EXPRESSION OF A CRYPTIC DEHALOGENASE GENE (DEHLL)

In appropriate environments containing 2-monochloropropionic acid (2MCPA), mutations in a population of nondehalogenating Pseudomonas putida, strain PP40-040 (parent population), resulted in the formation of 2mcpa(+) papillae as a result of the decryptification of a dehII gene. Increasing the size of the parent population, for example by increasing the availability of a metabolizable substrate such as succinate or lactate, increased the number of 2mcpa(+) papillae formed because there were more parent cells available for mutation to the 2mcpa(+) phenotype. The presence of a dehalogenating population, such as P, putida strain PP3, in close proximity to the non-dehalogenating population, also increased the number of 2mcpa(+) papillae formed. This was due to the excretion of dehalogenases into the growth medium, which caused localized dehalogenation of the available 2MCPA, yielding a metabolizable substrate. This substrate stimulated the growth of the non-dehalogenating population, in turn increasing the number of 2mcpa(+) papillae formed. Barriers, such as dialysis membranes, which prevented the excretion of the dehalogenases into the growth medium, prevented the stimulation of 2mcpa(+) papillae formation by preventing release of metabolizable substrates from 2MCPA breakdown. Cell-free extracts (CFE) from dehalogenase-producing populations had a similar effect for the same reason. CFE without dehalogenase activity or in which the dehalogenase activity had been destroyed by heating failed to stimulate parent population growth and 2mcpa(+) papillae formation. In the case of Pseudomonas putida strain PP3, which carries an easily transposed dehalogenase-encoding transposon, treatment of CFE with DNAase eliminated an additional factor involved in the formation of 2mcpa(+) papillae.