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

In appropriate environments containing 2-monochloropropionic acid (2MC PA), mutations in a population of nondehalogenating Pseudomonas putida , strain PP40-040 (parent population), resulted in the formation of 2m cpa(+) papillae as a result of the decryptification of a dehII gene. I ncreasing the size of the parent population, for example by increasing the availability of a metabolizable substrate such as succinate or la ctate, increased the number of 2mcpa(+) papillae formed because there were more parent cells available for mutation to the 2mcpa(+) phenotyp e. The presence of a dehalogenating population, such as P, putida stra in 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 locali zed dehalogenation of the available 2MCPA, yielding a metabolizable su bstrate. This substrate stimulated the growth of the non-dehalogenatin g population, in turn increasing the number of 2mcpa(+) papillae forme d. Barriers, such as dialysis membranes, which prevented the excretion of the dehalogenases into the growth medium, prevented the stimulatio n of 2mcpa(+) papillae formation by preventing release of metabolizabl e substrates from 2MCPA breakdown. Cell-free extracts (CFE) from dehal ogenase-producing populations had a similar effect for the same reason . CFE without dehalogenase activity or in which the dehalogenase activ ity had been destroyed by heating failed to stimulate parent populatio n growth and 2mcpa(+) papillae formation. In the case of Pseudomonas p utida strain PP3, which carries an easily transposed dehalogenase-enco ding transposon, treatment of CFE with DNAase eliminated an additional factor involved in the formation of 2mcpa(+) papillae.