Frequent occurrence of the ability to utilize octopine in rhizobacteria

Abstract

Over 200 strains of root-colonizing bacteria were tested for opine catabolism. Of these, 12% utilized octopine, 9% catabolized octopinic acid, and <1% used succinamopine. None grew on mannopine or nopaline. Most of the octopine and octopinic acid utilizers were pseudomonads. Only one Gram-positive bacterium used succinamopine. No strains of Serratia, Enterobacter, Aeromonas, or Bacillus catabolized an opine. All bacteria that were isolated from roots of arctic plants and selected for dinitrogen fixation utilized octopine after enrichment cycles with malate. Malate and glucose were compared for their ability to amplify, when used as selective substrates, the fraction of opine utilizers initially present in a plant sample. With this approach, <5% of 401 rhizobacteria tested utilized octopine, octopinic acid, or both opines. The opine-catabolizing strains belonged to the families Rhizobiaceae and Pseudomonadaceae and to the genera Alcaligenes and Flavobacterium. The relative effect of malate and glucose in the enrichment for opine utilizers varied according to the origin of the sample. In this study, octopine and to a lesser extent octopinic acid were recognized as substrates that were more commonly utilized by rhizobacteria than other opines. These results demonstrate that opine catabolism is not restricted to the genus Agrobacterium. Key words: octopine, rhizobacteria, Pseudomonadaceae, Alcaligenes, Flavobacterium.