DIVERSITY OF RETRON ELEMENTS IN A POPULATION OF RHIZOBIA AND OTHER GRAM-NEGATIVE BACTERIA

Genetic elements called retrons reside on the chromosome of Escherichi a coli and the myxobacteria and represent the first reverse transcript ase-encoding element to be found in a prokaryotic cell. All known retr ons produce a functionally obscure RNA-DNA satellite molecule called m ulticopy single-stranded DNA (msDNA). We report here the presence of m sDNA-producing retron elements in a number of new bacterial groups, in cluding strains of the genera Proteus, Klebsiella, Salmonella, Nannocy stis, Rhizobium, and Bradyrhizobium. Among a population of 63 rhizobia strains, only 16% contain a retron element. The rhizobia retrons appe ar to be heterogeneous in nucleotide sequence and show little similari ty to previously studied retrons of E. coli and the myxobacteria.