The nodulation of alfalfa by the acid tolerant Rhizobium sp. LPU83 does not require sulfated forms of lipo-chitooligosaccharide nodulation signals

TORRES TEJERIZO, G.; DEL PAPA, M. F.; SORIA-DIAZ, M. E.; DRAGHI, W. O.; LOZANO M.J.; GIUSTI M. A.; MANYANI, H.; MEGIAS, M; GIL SERRANO, A.; PÜHLER A.; NIEHAUS K.; LAGARES, A.; PISTORIO, M.

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Año: 2011 vol. 193 p. 30 - 39

0021-9193

The induction of root nodules by the majority of rhizobia has a strict requirement for the  secretion of symbiosis-specific lipochitooligosaccharides (nodulation factors [NFs]). The  nature of the chemical substitution on the NFs depends on the particular rhizobium and  contributes to the host specificity imparted by the NFs. We present here a description of  the genetic organization of the nod gene cluster and the characterization of the chemical  structure of the NFs associated with the broad-host-range Rhizobium sp. LPU83, a  bacterium capable of nodulating at least alfalfa, bean, and Leucena leucocephala. The nod  gene cluster was located on the plasmid pLPU83b. The organization of the cluster showed  synteny with those of the alfalfa-nodulating rhizobia, S. meliloti and S. medicae.  Interestingly, the strongest sequence similarity observed was between the partial nod  sequences of R. mongolense USDA 1844 and the corresponding LPU83 nod genes  sequences. The phylogenetic analysis of the intergenic region nodEG, positions strain  LPU83 and the type strain R. mongolense 1844 in the same branch, that fact indicates  that Rhizobium sp. LPU83might represent an early alfalfa nodulating genotype. The NFs  chemical structures obtained for the wild-type strain consist of a trimeric, tetrameric, and  pentameric chitin backbone that shares some substitutions with both alfalfa- and bean40 dulating rhizobia. Remarkably, while in strain LPU83 most of the NFs were sulfated  in their reducing-terminal residue, none of the NFs isolated from the nodH mutant  LPU83-H were sulfated. The evidence obtained supports the notion that the sulfate  decoration of NFs in LPU83 is not necessary for alfalfa nodulation.