A NEW MUTATION IN THE PUFL GENE RESPONSIBLE FOR THE TERBUTRYN RESISTANCE PHENOTYPE IN RUBRIVIVAX-GELATINOSUS

Rubrivivax gelatinosus is a facultative phototrophic non-sulfur bacter ium belonging to the beta subclass of the purple bacteria. A terbutryn -resistant mutant of R. gelatinosus has been isolated and characterize d. Increased resistance levels to terbutryn (300-fold), atrazine (6-fo ld) and o-phenanthroline (3-fold) were observed for the mutant compare d with wild type. Sequence analysis of the mutant revealed a new mutat ion in the pufL gene coding for the L subunit of the reaction centre ( RC) at codon 192 leading to an amino-acid substitution from Gly in the wild type to Asp in the mutant. This substitution is located in the D helix of the L subunit, suggesting an interaction between terbutryn a nd this part of the polypeptide in the RC of R. gelatinosus. This is t he first report of a mutation leading to herbicide resistance and affe cting the D helix in purple bacteria. Furthermore R. gelatinosus wild type is highly sensitive to o-phenanthroline compared with other purpl e bacteria (Rhodobacter capsulatus and Rhodobacter sphaeroides). Seque nce comparison of the L subunit from six purple bacteria in which o-ph enanthroline sensitivity was measured suggests that Ser(L226) might be responsible for this phenotype.