Photosynthetic Bradyrhizobia from Aeschynomene spp. Are Specific to Stem-Nodulated Species and Form a Separate 16S Ribosomal DNA Restriction Fragment Length Polymorphism Group

Abstract

We obtained nine bacterial isolates from root or collar nodules of the non-stem-nodulated Aeschynomene species A. elaphroxylon, A. uniflora, or A. schimperi and 69 root or stem nodule isolates from the stem-nodulated Aeschynomene species A. afraspera, A. ciliata, A. indica,A. nilotica, A. sensitiva, and A. tambacoundensis from various places in Senegal. These isolates, together with 45 previous isolates from variousAeschynomene species, were studied for host-specific nodulation within the genus Aeschynomene, also revisiting cross-inoculation groups described previously by D. Alazard (Appl. Environ. Microbiol. 50:732–734, 1985). The whole collection ofAeschynomene nodule isolates was screened for synthesis of photosynthetic pigments by spectrometry, high-pressure liquid chromatography, and thin-layer chromatography analyses. The presence ofpuf genes in photosyntheticAeschynomene isolates was evidenced both by Southern hybridization with a Rhodobacter capsulatus photosynthetic gene probe and by DNA amplification with primers defined from photosynthetic genes. In addition, amplified 16S ribosomal DNA restriction analysis was performed on 45 Aeschynomeneisolates, including strain BTAi1, and 19 reference strains fromBradyrhizobium japonicum, Bradyrhizobium elkanii, and other Bradyrhizobium sp. strains of uncertain taxonomic positions. The 16S rRNA gene sequence of the photosynthetic strain ORS278 (LMG 12187) was determined and compared to sequences from databases. Our main conclusion is that photosynthetic Aeschynomene nodule isolates share the ability to nodulate particular stem-nodulated species and form a separate subbranch on the Bradyrhizobium rRNA lineage, distinct from B. japonicum and B. elkanii.

Characterization of the common nodulation genes of the photosynthetic Bradyrhizobium sp. ORS285 reveals the presence of a new insertion sequence upstream of nodA

“…Sequence similarity of NodA from those photosynthetic strains with other NodA Bradyrhizobium species was low (63%). These data are in full agreement with previous phylogenetic studies, which showed that photosynthetic Aeschynomene strains form a homogeneous and distinct cluster [3], for which a new species should be proposed. Conversely, NodA sequences from the non-photosynthetic Group I and II strains intertwined with the other species of Bradyrhizobium (Fig.…”

“…In spite of testing numerous primers de¢ned from the consensus region of either NodA, NodB or NodC, we did not succeed in isolating the common nod genes from Group III photosynthetic strains. These results indicate a great divergence of the symbiotic genes as compared with the other rhizo- Acacia nilotica II + [3] bia, which could be related to the extreme narrow host-speci¢city of the Group III photosynthetic strains. Sequence analysis revealed that the nodA gene sequences from Groups I and II non-photosynthetic Bradyrhizobiumtested strains are polymorphs with a percentage of similarity ranging from 73.78 to 96.62% at the DNA level.…”

“…Conversely, NodA sequences from the non-photosynthetic Group I and II strains intertwined with the other species of Bradyrhizobium (Fig. 1), and the sequence similarity for this genus was high, ranging from 80 to 88%, thus con¢rming their taxonomic position within the Bradyrhizobium japonicum and Bradyrhizobium elkanii branches [3].…”

“…The two other groups, II and III, develop stem nodulation. Group III is exclusively nodulated by photosynthetic rhizobia, which are highly speci¢c to that group [3]. Group II is intermediary as it is nodulated by both non-photosynthetic Bradyrhizobium, and with photosynthetic strains which are also able to nodulate Group III [3].…”

The microbial diversity of a storm cloud as assessed by hailstones

“…They may therefore grow on atmospheric methanol and consequently alter atmospheric chemistry. Bacterial strains belonging to the genus Bradyrhizobium fix nitrogen, and several Bradyrhizobium strains can carry out photosynthesis (Molouba et al, 1999). Their diverse metabolic capacities could be an advantage in the atmospheric environment, where at least some bacteria may be limited with bioavailable organic compounds.…”